Beer fermentation technology

The beer fermentation process is a normal life activity carried out by brewer's yeast under certain conditions, using fermentable substances in the wort, and the product of its metabolism is the desired product, beer. Due to the different types of yeast, the fermentation conditions and product requirements and flavors are different, and the way of fermentation is also different. Depending on the type of yeast fermentation beer can be divided into top-fermented beer and bottom-fermented beer. Beer fermentation techniques can generally be divided into traditional fermentation techniques and modern fermentation techniques. Modern fermentation mainly involves cylindrical open-air conical fermenters fermentation, continuous fermentation and highly concentrated dilute fermentation, mainly using cylindrical open-air conical fermenters fermentation.

Process Flow

Oxygenated cold wort → fermentation → pre-fermentation → main fermentation → post-fermentation → storage → fresh beer→ Strain

Fermentation technology 

Modern fermentation technology mainly includes large-capacity fermenter fermentation method (which is mainly cylindrical open-air conical fermenter fermentation method), dilution fermentation method after high concentration saccharification, continuous fermentation method, etc.

(a) Conical fermenter fermentation method

Traditional beer is carried out in a square or rectangular fermentation tank (or pool), equipment volume of only 5 ~ 30m, small-scale beer production, long production cycle. 1950s onwards, due to the rapid development of the world economy, the scale of beer production increased significantly, the traditional fermentation equipment to meet the needs of production, large-capacity fermentation equipment has received attention. The so-called large-capacity fermenter refers to the volume of the fermenter compared with traditional fermentation equipment. Large-capacity fermenters are cylindrical conical fermenters, asahi tanks, universal tanks and spherical tanks. The cylindrical conical fermenter is the world's common fermenter, the main body of the tank is cylindrical, the top of the tank is arc-shaped, the bottom is conical, with a considerable height (height is greater than the diameter), the tank is equipped with cooling and insulation devices, a fully enclosed fermenter. The cylindrical conical fermenter is suitable for both the bottom fermentation and the top fermentation, processing is very convenient. German brewer invented vertical cylindrical conical fermenter due to its many advantages, after continuous improvement and development, and gradually promoted and used around the world. Since the mid-1970s, China began to use outdoor cylindrical conical bottom fermentation tank fermentation method (referred to as conical tank fermentation method), almost all domestic beer production using this fermentation method.

1 Conical tank fermentation method features

(1) The bottom is conical to facilitate the discharge of yeast at any time during the production process, requiring the use of cohesive yeast.

(2) The tank itself has a cooling device, which facilitates the control of fermentation temperature. The production is easy to control, the fermentation cycle is shortened, there is less chance of contamination, and the quality of beer is stable.

(3) The tank is equipped with heat preservation device outside, which can place the tank outside, reduce construction investment, save floor space and facilitate expansion.

(4) The use of closed tank is convenient for CO2 washing and CO2 recovery, and the fermentation can be carried out under certain pressure. It can be used as fermentation tank and wine storage tank, or fermentation and wine storage can be combined into one, called one tank fermentation method.

(5) The fermentation solution in the tank produces a CO2 gradient due to the height of the liquid (i.e., a density gradient is formed). By cooling control, the fermentation broth can be subjected to natural convection, and the higher the tank, the stronger the convection. Due to the existence of strong convection, the yeast fermentation capacity is increased, the fermentation speed is accelerated, and the fermentation cycle is

 shortened.

(6) The fermentation tank can be controlled by instrument or microcomputer, easy to operate and manage.

(7) The conical tank is applicable to both below and above fermentation.

(8) CIP automatic cleaning device can be used, easy to clean.

(9) The conical tank is easy to process (can be processed on site) and has strong practicality.

(10) The capacity of the equipment can be flexibly adjusted according to the production needs, and the capacity can vary from 20 to 600m, up to 1500m.

2. Conical tank working principle and tank structure

(1) Conical fermenter working principle

The reason for the short fermentation cycle and fast fermentation speed of the conical tank fermentation method is due to the hydrodynamic characteristics of the fermentation broth in the conical tank and the result of modern beer fermentation technology adopted.

After inoculating yeast, due to the coagulation of yeast, the cell density of yeast at the bottom of the tank increases, resulting in faster fermentation and more carbon dioxide produced in the fermentation process, and at the same time, due to the hydrostatic pressure generated by the height of the liquid column of fermentation broth, it also makes the carbon dioxide content change in a gradient with the change of liquid layer (see Table 4-3-1), so the density of fermentation broth in the tank also shows a gradient change, in addition, due to the conical tank In addition, since the conical tank is equipped with a cooling device outside the body, the temperature of each stage of fermentation can be controlled artificially. Under the driving forces of hydrostatic pressure difference, fermentation broth density difference, carbon dioxide release effect and temperature difference (1~2℃) generated by cooling of the upper part of the tank, the fermentation broth inside the tank produces strong natural convection, which enhances the contact between yeast and fermentation broth and promotes the metabolism of yeast, making beer fermentation speed up greatly and beer fermentation cycle shorten significantly. In addition, the increased inoculation temperature, beer main fermentation temperature, diacetyl reduction temperature and yeast inoculation amount are also conducive to accelerating yeast fermentation, thus enabling fermentation to proceed quickly.

(2) Basic structure of conical fermenter

①Tank top part

The top of the tank is a dome-shaped structure with a central hole for a removable large-diameter flange to install CO2 and CIP piping and their connections, an anti-vacuum valve, an overpressure valve and a pressure sensor, etc. The inside of the tank is equipped with a washing device and a platform and access for top operation.

②Tank body part

The tank body is a cylinder, which is the main part of the tank. The height of the fermentation tank depends on the diameter and height of the cylinder. Due to the large diameter of the tank and low pressure resistance, the general diameter of the conical tank does not exceed 6 m. The processing of the tank body is easier than the top of the tank, the outside of the tank body is used to install cooling devices and insulation, and leave a certain location to install temperature and pressure measurement components. The tank part of the cooling layer has a variety of forms, such as coils, Miller wrench, jacketed, and divided into 2 to 3 sections, with pipes leading to the cooling medium into the pipe connected to the cooling layer covered with polyurethane foam plastic and other insulation materials, insulation and then wrapped in a layer of aluminum or stainless steel plate, there are also the use of color steel for the protective layer.

③Cone bottom part

Conical bottom angle is generally 60 & ordm; ~ 80 & ordm;, there are 90 & ordm; ~ 110 & ordm;, but this is mostly used for large-capacity fermenter. The height of the conical bottom of the fermentation tank is related to the angle, the smaller the angle the higher the conical bottom part. The general height of the cone bottom of the tank accounts for about 1/4 of the total height, do not exceed 1/3. The outer wall of the cone bottom should be equipped with a cooling layer to cool the yeast precipitated at the bottom of the cone. Cone bottom should also be installed in and out of the pipeline, valve, sight glass, temperature measurement, pressure measurement to sensing elements, etc..

In addition, the diameter of the tank and height ratio is usually 1:2 ~ 1:4, the total height is best not to exceed 16m, so as not to cause strong convection, affecting the yeast and solidification of the settlement. Tank material can be made of stainless steel or carbon steel. If carbon steel is used, the inner wall of the tank must be coated with a non-toxic paint that has no effect on the taste of beer. The working pressure of the fermentation tank can be determined according to the working nature of the tank, the general working pressure of the fermentation tank is controlled at 0.2 to 0.3 MPa. The inner wall of the tank must be smooth and flat, the inner wall of the stainless steel tank should be polished, and the inner wall of the carbon steel tank should be evenly coated, without concave or convex surface and without granular projection.

(3) the main dimensions of the conical fermenter to determine

① diameter to height ratio conical tank is cylindrical cone bottom shape, the diameter of the cylinder body and the height of the ratio of 1: 1 ~ 4. Generally the larger the diameter to height ratio, the stronger the natural convection during fermentation, yeast fermentation speed, but yeast is not easy to settle, beer clarification difficulties. General diameter and the total height of the wort level ratio should be 1:2, diameter and columnar part of the wort height ratio should be 1:1 ~ 1.5.

② Tank capacity The larger the tank capacity, the longer the wort full tank time, the more times the fermentation proliferates, the longer the time, it will cause the diacetyl precursors to increase the amount of formation, diacetyl production, long reduction time. In addition, it will cause longer non-production time such as discharging, cleaning and re-feeding wort, and the peak peak of cold use is high, which will cause tension in cooling supply. Due to the release of carbon dioxide and foam production, the effective volume of the tank is generally about 80% of the total tank volume.

③ cone angle Generally between 60 ° ~ 90 °, commonly used 60 ° ~ 75 ° (stainless steel tanks commonly used cone angle of 60 °, inside the steel tank with paint cone angle of 75 °), in order to facilitate the settlement and separation of yeast.

④ Cooling jacket and cooling area Conical fermenter cooling is often used indirect cooling. Domestic generally use semi-circular tube, channel steel, curved tube jacket, or Miller plate's jacket in low temperature and low pressure (-3 ℃, 0.03 MPa) with liquid secondary refrigerant cooling, foreign countries mostly use heat exchange piece type (explosion molding) one-time refrigerant direct evaporative cooling. Primary cold enzyme (such as liquid ammonia evaporation temperature of -3 ~ -4 ℃) after evaporation pressure of 1.0MPa ~ 1.2MPa, the jacket pressure resistance requirements are high. Since the freezing point temperature of beer is generally -2.0～-2.7℃, the refrigerant temperature should be around -3℃ in order to prevent the beer from freezing locally in the tank. Domestic often use 20% to 30% of alcohol aqueous solution, or 20% propylene glycol aqueous solution as the refrigerant.

Depending on the capacity of the tank, cooling can be two-stage or three-stage type. The cooling area depends on the material of the tank, stainless steel material is generally 0.35 ~ 0.4m/m fermentation solution, carbon steel tank is 0.5 ~ 0.62m/m fermentation solution. The cone bottom cooling area should not be too large to prevent icing of beer during the storage period.

⑤ insulation layer and protective layer insulation layer materials require small thermal conductivity, low volume mass, less water absorption, non-combustible and other characteristics. Commonly used insulation materials are polyamide resin, self-extinguishing polystyrene plastic, polyurethane, expanded perlite powder and slag wool. Insulation layer thickness is generally 150 ~ 200mm. outer protective layer is generally used 0.7 ~ 1.5mm thick aluminum alloy plate, tin plate or 0.5 ~ 0.7mm stainless steel plate, recently corrugated plate is more popular.

(6) tank pressure resistance Fermentation produces a certain amount of carbon dioxide to form the top pressure of the tank (tank pressure), should be equipped with a carbon dioxide adjustment valve, the top of the tank with a safety valve. When the carbon dioxide is discharged, the speed of downing wine is too fast, and the carbon dioxide dissolves when the fermentation tank is washed, etc. will cause negative pressure in the tank, so a vacuum valve must be installed. Back pressure of carbon dioxide or compressed air should be used before putting down the wine to avoid negative pressure in the tank, which will cause the fermenter to "deflate".

3. Conical tank fermentation process

(1) Combination form of conical tank fermentation

Conical tank fermentation production process combination forms are as follows.

①Fermentation - storage type In this way, the requirements of the two tanks are different and the pressure resistance is also different, which is not significant for modern brewing.

② Fermentation - post-treatment type That is, one tank is used for fermentation and the other tank is used for post-ripening treatment. For the fermentation tank, the fermentable components are finished at once, basically no fermentable components are retained, and all the CO2 produced by fermentation is recovered and stored for backup, and then transferred to the post-treatment tank for post-maturation treatment. The process is to separate the fermentation broth at the end of fermentation by centrifugation to remove yeast and cold solids, then cool it to storage temperature by thin plate heat exchanger, and start filtering after 1 to 2 days of low temperature storage.

(3) Fermentation-post-adjustment type That is, the previous fermentation tank is similar to the one-tank method for fermentation, wine storage, completion of fermentation of fermentable components, recovery of CO2, recovery of yeast, CO2 washing, and after appropriate low-temperature storage, adjustment of color, stability, CO2 content and other indicators in the post-adjustment tank, and then after appropriate stabilization, the filtration operation can be started.

(2) Determination of main process parameters of fermentation

①Fermentation cycle

Determined by product type, quality requirements, yeast performance, inoculum amount, fermentation temperature, season, etc., generally 12 to 24 days. Usually, the fermentation cycle of common beer is shorter in summer, the fermentation cycle of high quality beer is longer, and the fermentation cycle of off-season is extended appropriately.

② Yeast inoculation amount

It is generally decided according to yeast performance, generation, aging condition, product type, etc. The size of inoculum is determined by the number of yeast after adding yeast. At the beginning of fermentation: 10～20×10/ml; at the peak of fermentation: 6～7×10/ml; after yeast discharge: 6～8×10/ml; when storing wine around 0℃: 1.5～3.5×10/ml.

③The highest fermentation temperature and diacetyl reduction temperature

The temperature at which beer ferments vigorously is called the highest fermentation temperature. Generally, beer fermentation can be divided into three types: low-temperature fermentation, medium-temperature fermentation and high-temperature fermentation. Low temperature fermentation: vigorous fermentation temperature of about 8℃; medium temperature fermentation: vigorous fermentation temperature of 10～12℃; high temperature fermentation: vigorous fermentation temperature of 15～18℃. Domestic general fermentation temperature is: 9～12℃. Diacetyl reduction temperature is the temperature at the end of vigorous fermentation when the beer is in the post-ripening stage (mainly to eliminate diacetyl), and generally the diacetyl reduction temperature is equal to or higher than the fermentation temperature, which not only ensures the quality of beer but also helps to shorten the fermentation cycle. If the fermentation temperature is increased, the fermentation cycle is shortened, but the increase in the amount of metabolic by-products will affect the flavor of beer and easily stain bacteria; if the diacetyl reduction temperature is increased, the maturation time of beer is shortened, but it is easy to stain bacteria and is not conducive to yeast precipitation and beer clarification. Low temperature prolongs the fermentation cycle.

④Tank pressure

Depending on the type of product, wort concentration, fermentation temperature and yeast strain, etc., it is determined. The highest tank pressure is generally controlled at 0.07 to 0.08 MPa during fermentation, and the highest tank pressure is generally the highest fermentation temperature value divided by 100 (unit MPa). The use of fermentation with pressure can inhibit the proliferation of yeast, reduce the phenomenon of excessive metabolic by-products caused by heating, prevent the generation of excessive advanced alcohols and esters, and at the same time facilitate the reduction of diacetyl and ensure the CO2 content of the wine. The relationship between CO2 content in beer and tank pressure and temperature is

CO2 (%, m/m) = 0.298 + 0.04p - 0.008t

where p - tank pressure (pressure gauge reading) (MPa)

t - beer pint temperature (℃)

⑤ Full tank time

The time required from the first batch of wort into the tank to the last batch of wort into the tank is called full tank time. Full tank time is long, yeast proliferation is large, produce metabolic by-products α-acetyl lactic acid more, diacetyl peak high, generally in 12 ~ 24h, preferably within 20h.

⑥Fermentation degree

It can be divided into low fermentation degree, medium fermentation degree, high fermentation degree and ultra-high fermentation degree. For light beer fermentation degree is divided into: low fermentation degree beer, its real fermentation degree 48% ~ 56%; medium fermentation degree beer, its real fermentation degree 59% ~ 63%; high fermentation degree beer, its real fermentation degree 65% or more, ultra-high fermentation degree beer (dry beer) its real fermentation degree in 75% or more. Domestic more popular fermentation degree higher light refreshing beer.

(4) Conical fermenter process requirements

①The quality of raw materials and saccharification effect should be effectively controlled, and the composition of each batch of wort should be even, if the composition of each batch of wort differs too much, it will affect the yeast reproduction and fermentation. Such as 10ºP wort composition requirements are: concentration % (m/m) 10±0.2, color (EBC unit) 5.0~8.0, pH5.4±0.2, α-amino nitrogen (mg/L) 140~180.

②The capacity of the large tank should be adapted to the amount of cold wort to be saccharified each time and the number of saccharifications per day, requiring a tank to be filled within 16h, not more than 24h at most, and the cold wort into the tank should be removed as much as possible for hot solids, and it is better if the cold solids can be separated as much as possible.

③The temperature control of cold wort should consider the time interval of each wort into the can and the number of full cans, if the interval time is long and the number is many, we can consider raising the temperature of wort batch by batch, we can also consider the first one or two batches without adding yeast, and after that the full amount of yeast will be added in a certain proportion, adding the proportion from small to large, but we should pay attention to avoid wort staining bacteria. There is also the method of adding yeast to the first few batches of wort and not adding yeast to the last batch of wort.

④The control of dissolved oxygen of cold wort can be determined according to the amount of yeast added and yeast reproduction, and it is generally required that each batch of cold wort should be oxygenated as required, and the dissolved oxygen of mixed cold wort should not be less than 8mg/L.

⑤ Control the fermentation temperature should be kept relatively stable to avoid sudden high and low. The temperature control is better to use automatic control.

⑥CO2 recovery should be carried out as much as possible to facilitate CO2 washing, CO2 replenishment in wine and CO2 back pressure, etc.

(7) The fermentation tank should preferably be made of stainless steel to facilitate cleaning and sterilization. When using carbon steel to make the fermentation tank, the coating layer should be kept uniform and firm, and the surface should not be uneven, and the coating should not fall off during use. Fermentation tank should be equipped with high pressure spray washing device, spray washing pressure should be controlled at 0.39~0.49MPa or higher.

(5) Operation steps (one tank method fermentation)

①Inoculation Select the 0 generation yeast that has been cultivated or the fermentation tank yeast that has normal fermentation sugar reduction in production, fast diacetyl reduction and qualified microbiological index as seed, the latter can be seeded in series by using the can-can method. The seeding amount is based on the yeast number in (1.2~1.5) x 10/ml after full tank.

②Full tank time Under normal circumstances, the full tank time is required to be no more than 24h, and the expansion can be based on the inspired situation. Discharge cold condensate every 1 day after full tank, 3 times in total.

③Main fermentation temperature 10℃, 10±0.5℃ for common wine,9±0.5℃ for high quality wine, which can be increased by 0.5℃ in peak season. When the appearance of brix drops to 3.8%~4.2%, the tank can be sealed and pressurized. Fermentation tank pressure control at 0.10 ~ 0.15MPa.

④ Diacetyl reduction After the main fermentation is finished, turn off the refrigerant and raise the temperature to 12℃ for diacetyl reduction. When the diacetyl content drops to below 0.10mg/L, start cooling down.

⑤Cooling down After diacetyl reduction is finished, lower the temperature from 12℃ to 5℃ within 24h and stay for 1 day for yeast recovery. Yeast can also be recovered during fermentation at 12℃ to ensure more highly active yeast. In peak season or when there is not enough yeast, yeast can be recovered directly after the main fermentation is finished.

(6) Wine storage After yeast recovery, the conical tank continues to cool down and bring the temperature down to -1℃～-1.5℃ within 24h and store the wine at this temperature. Storage time: more than 7 days in low season, more than 3 days in high season.

4. Yeast recovery

The yeast recovery method of conical tank fermentation method is different from traditional fermentation, the main differences are: the recovery time is not fixed, the yeast can be discharged at any time after the beer cools down to 6~7℃, while traditional fermentation can only be carried out after the fermentation is finished; the recovery temperature is not fixed, it can be carried out at 6~7℃, or at 3~4℃ or 0~1℃; the number of recovery is not fixed, the yeast recovery in conical tank can be carried out in several times The recovery is carried out mainly for several times according to the actual needs; the way of recovery is different, generally using yeast recovery pump and metering device, pressurization and oxygenation device, while equipped with yeast tank and larger volume, which can accommodate several tanks of recovered yeast (the same or similar generations); the way of storage is different, conical tanks generally do not carry out yeast washing, storage temperature can be adjusted, and storage conditions are better.

In general, yeast should be recovered in time when the temperature drops below 6-7℃ at the end of fermentation. If yeast recovery is not timely, the yeast at the bottom of the cone will soon appear "autolysis". Before recovering yeast, the valve of cone bottom should be sterilized with 75% (v/v) alcohol solution cotton ball, and the pipeline for recovering or adding yeast should be washed with 85℃ NaOH (commonly called fire alkali) solution for 20 minutes regularly; before each use of pipeline, first pass 85℃ hot water for 30 minutes and 0.25% disinfection solution (H2O2, etc.) for 10 minutes; after use of pipeline, first rinse with water for 5 minutes, then use 85℃ hot water Sterilize for 20 minutes.

The more generations of yeast used, the more contamination of anaerobic bacteria will generally increase, and it is best not to use more than 4 generations of yeast. Do not recycle yeast contaminated by anaerobic bacteria, it is better to do sterilization before discharge.

Pay attention to when recovering yeast: to recover slowly, to prevent yeast in the pressure suddenly lowered causing yeast cell rupture, it is best to prepare pressure properly; to remove the upper and lower yeast, recover the middle strong yeast; yeast recovery after storage temperature 2 ~ 4 ℃, storage time should not exceed 3 days.

After yeast slurry recovery, add 2~3 times of 0.5~2.0℃ sterile water dilution in time, filter through 80~100 purpose yeast sieve to remove impurities, and wash 2~2.5 times a day.

If the recycled yeast mud contaminated with miscellaneous bacteria can be acid washing: edible grade phosphoric acid, diluted to 5% with sterile water (m/m), added to the recycled yeast mud, modulating pH 2.2 ~ 2.5, stirring evenly after standing for more than 3h, pour away the upper layer of acid water can be put into use. After acid washing, it can kill more than 99% of bacteria.

Yeast use generation: Some people found that under the same conditions, 2 generations of yeast fermentation cycle is longer, but the ability of sugar reduction and diacetyl reduction is better; 3 generations of yeast in the fermentation cycle, sugar reduction, diacetyl reduction ability and other aspects of the best, yeast activity is the strongest; 4 generations of yeast later, the fermentation cycle is gradually extended, the yeast sugar reduction ability and diacetyl reduction ability also gradually decreased, product quality will become poor.

If the wort is rich in nutrients (high content of α-amino nitrogen, more than 180mg/L), the recovered yeast activity is high, while when the wort is lacking in nutrients, the recovered yeast activity is poor, which has obvious influence on the next round of fermentation and beer quality.

When recovering yeast slurry, the yeast mortality rate is measured by 0.01% of US blue staining, if the mortality rate exceeds 10%, it can't be used again, generally the mortality rate of recovered yeast should be below 5%.

5. CO2 recovery

CO2 is an important by-product of beer production, according to theoretical calculation, every 1kg of maltose fermentation can produce 0.514kg of CO2, and every 1kg of glucose can produce 0.489kg of CO2, the actual fermentation of the first 1 to 2 days of CO2 is not pure, can not be recovered, the actual recovery rate of CO2 is only 45% to 70% of the theoretical value. The empirical data is that the actual recovery of CO2 per 100 liters of wort in the beer production process is about 2 to 2.2 kg.

The CO2 recovery and use process flow is as follows

CO2 collection → washing → compression → drying → purification → liquefaction and storage → gasification → use

①Collection of CO2 After 1 day of fermentation, the purity of the discharged CO2 is checked to be 99% to 99.5% or more, and the pressure of CO2 is 100-150kPa, and the foam and trace alcohol and fermentation by-products are removed through the foam trap and water washing tower, which are continuously fed into the rubber air bladder to make the CO2 recovery equipment operate continuously and evenly.

②Washing CO2 enters the water washing tower and goes up against the flow, while water is sprayed down from above. Some are also equipped with potassium permanganate scrubbers, which can remove organic impurities from the gas.

③Compression The washed CO2 gas is compressed in 2 stages by the oil-free CO2 compressor. The first stage is compressed to 0.3MPa (gauge pressure) and condensed to 45℃; the second stage is compressed to 1.5~1.8MPa (gauge pressure) and condensed to 45℃.

④Drying After 2 stages of compression, CO2 gas (about 1.8 MPa) enters a dryer equipped with silica gel or molecular sieve to remove water vapor from CO2 and prevent icing. Drying is also placed after the purification operation.

⑤Purification After drying, the CO2 is purified by an activated carbon filter. The filter is equipped with activated carbon to remove microscopic impurities and odors from the CO2 gas. It is required that 2 units are connected in parallel, one of which is regenerated for backup, with electric heating device inside, and some are regenerated with steam, and it is required that it should be regenerated 1 time within 37h.

(6) Liquefaction and storage After being dried and purified, CO2 gas is passed through the column tube CO2 purifier. When the CO2 gas flowing in the column tube condenses to below -15℃, it turns into liquid CO2 at -27℃ and 1.5MPa and enters the storage tank, and the refrigerant R22 flowing outside the column tube is evaporated and inhaled into the chiller.

(7) Gasification The storage tank pressure of liquid CO2 is 1.45MPa (between 1.4 and 1.5), and the liquid CO2 is transformed into gaseous CO2 by steam heating evaporation device and delivered to each gas-using electricity.

The purity of recovered CO2 should be greater than 99.8% (v/v), of which the maximum content of water is 0.05%, the maximum content of oil is 5mg/L, the maximum content of sulfur is 0.5mg/L, and the maximum content of residual gas is 0.2%, and the unpleasant taste and odor cannot appear when dissolving CO2.

6. Cleaning and disinfection of conical tanks

In beer production, hygiene management is crucial. The direct consequence of not strict cleaning and disinfection sterilization in the production process is: light pollution makes the beer taste poor, short shelf life and poor quality; serious pollution can make the beer sour and scrapped.

(1) Microbial control of fermentation tanks Beer fermentation is purely beer yeast fermentation, the pollution of harmful microorganisms in the fermentation process is spread through wort cooling operation, conveying pipes, valves, inoculated yeast, fermentation empty tanks, etc., while fermentation empty tanks are the largest source of pollution. Therefore, the beer fermentation tank must be washed and sterilized.

(2) Selection of biocides Equipment, methods and biocides play a decisive role in the quality of large tank washing, while the selection of economic, efficient and safe disinfection biocides is the key. Most of the biocides used in China's breweries are roughly CIO2, hydrogen peroxide, peroxyacetic acid, formaldehyde, etc. The best effect is the use of CIO2.

(3) the choice of washing methods

Although the cost of washing is low, it cannot fully kill all microorganisms and will have an impact on the taste of beer. It is also used to sterilize the brewery by washing with formaldehyde regularly, but it is not safe.

② Clear water - alkaline water - clear water - bactericides (CIO2, peracetic acid, hydrogen peroxide) It is generally believed that the final decomposition products of the above three disinfectants are non-toxic and do not need to be rinsed after washing. There are more manufacturers using this method, and their beer quality, especially taste and shelf life, will be improved by a grade compared to the first method.

③ Clear water - alkaline water - clear water - disinfectant - sterile water Some manufacturers believe that this method is safer for microbial control and can avoid side effects in case of residual disinfectant, but if the sterile water bacteria control is not qualified it will also bring repeated contamination of large tanks.

④ Clear water - dilute acid - clear water - alkaline water - clear water - sterilant - sterile water This method is considered to be a more ideal washing method. Through the inspection of the inner wall of large cans used for a long time, beer stones consisting of calcium oxalate, calcium phosphate and organic matter can be found adhering to them. The beer stones are first removed with dilute acid (phosphoric acid, nitric acid, sulfuric acid), and then washed and sterilized, which will be beneficial to the quality of beer.

(4) The influence of other factors on large tank washing

① Design of CIP system: Especially the angle of pipeline, the capacity and distribution of washing tank, and the recovery method of washing water will have an impact on washing sterilization. Some use with pressure recovery washing water, too high pressure will make washing water injection resistance and affect the washing effect.

② scrubber: the current production of many types of scrubbers, should choose the jet angle completely, not easy to block the universal scrubber. Regularly disassemble the top cover of the large tank to check the scrubber so that the scrubber will not be blocked by foreign objects.

③Washing pump and pressure: If the pressure of the pump is too small, the washing liquid will be sprayed weakly and will also leave dead space on the inner wall of the big tank, and the pressure of washing should generally be controlled at 0.25~0.4MPa.

④ Large tank wall: Some large tank walls with epoxy resin or T541 coating anti-corrosion, after a period of use will blister or peel off, if not timely inspection and maintenance, it will be in these dead ends hidden bacteria and contaminated beer.

⑤ Washing time: As long as the method is correct and the equipment is normal, generally clear water rinsing 15-20 minutes each time, alkaline washing time 20 minutes, sterilization time 20-30 minutes, the total time control in 90-100 minutes is more ideal.

⑥microscopic inspection sampling method: after the large tank washing is completed put clean water, close the bottom valve for a few minutes, and then open it again, with a sterile test tube or sterile triangular bottle, sampling on the flame for sterile flat dish culture for 24 hours or anaerobic bacteria culture for 7 days, incorrect sampling method or culture is not strict will also make microbiological determination inaccurate.

Abnormal treatment 

1. Fermentation solution "tumbling" phenomenon (resulting in slow clarification of liquor, filtering difficulties, poor quality)

Causes: mainly due to improper opening of the cooling jacket, resulting in the upper temperature deviation from the process curve 1.5 ~ 4 ℃, the middle of the tank temperature is higher, causing strong convection of fermentation broth. In addition, the pressure is unstable, sharp rise and fall can also cause tumbling.

Solution: Check whether the instrument is normal; strictly control the cooling temperature to avoid the upper liquor temperature is too high; keep the pressure in the tank stable.

2. Fermentation tank icing

When the lower temperature of the tank deviates from the process curve by about 2°C, it will cause the temperature inside the tank to reach the freezing point of beer (-1.8 to 2.3°C) during the storage period, which may lead to ice formation near the cooling zone.

The empirical formula for the freezing point temperature of beer is

G =-A×0.42+P×0.04+0.02

Where A - alcohol content in beer m/m%

P - original wort concentration m/m%

G - freezing point ℃

Reasons for icing: instrument failure, improper selection of temperature parameters, inappropriate depth of RTD installation position, poor instrument accuracy, improper operation, etc.

Solutions: check the temperature measuring components and instrument error, especially check whether the platinum resistance is leaking, if leaking should be baked and then paraffin sealed or replaced; choose proper temperature measuring point position and RTD insertion depth; strengthen process management, timely discharge of yeast; refrigerant liquid temperature should be controlled at -2.5～-4℃, can't use -8℃ refrigerant liquid.

3. Yeast autolysis

Cause: When the temperature difference between the lower part of the tank and the middle and lower part of the tank is more than 1.5～5℃, it will cause yeast settling difficulty and yeast autolysis phenomenon. The temperature of yeast slurry at the bottom of the tank is too high (16～18℃) and maintained for too long, which will also cause yeast autolysis and produce yeast smell, and sometimes there will be cloudy beer after sterilization.

Solutions: check whether the meter is normal; discharge yeast sludge in time; keep the refrigerant temperature at -4℃, and keep the upper, middle and lower temperatures between -1 and 1℃ during the storage period.

4. Drinking beer after the "head" phenomenon

Cause: Generally, when the content of senior alcohol in beer exceeds 120mg/L, isobutanol exceeds 10mg/L and isoamyl alcohol exceeds 50mg/L, it will cause the phenomenon of "headache" after drinking beer.

Solution: Use yeast strain with low advanced alcohol production; increase the amount of yeast added appropriately, reduce the amount of yeast proliferation, and the number of yeast cells should be 15×10/ml; control the α-amino nitrogen content of 12°P wort at about 180±200mg/L; control the dissolved oxygen content in wort at 8-10mg/L; control the fermentation temperature and tank pressure.

5. Diacetyl reduction difficulties

The diacetyl content after fermentation is over has been too high to meet the requirements.

The reasons for this phenomenon are: low α-amino nitrogen content in wort, more α-acetyl lactate produced by metabolism, resulting in high peak diacetyl and delayed reduction; taking high temperature and rapid fermentation, high fermentable sugar content in wort, high yeast proliferation, which is conducive to diacetyl formation; premature yeast settlement in the late stage of main fermentation, too little yeast suspended in the fermentation broth, poor diacetyl reduction ability; the yeast used aging or poor ability of yeast to reduce diacetyl, etc.

Solutions: control the content of α-amino nitrogen in wort (160-200mg/L), avoid too high or too low; appropriately increase the yeast inoculum and full tank temperature, and raise the diacetyl reduction temperature appropriately; the fermentation temperature should not be too high, and use pressurized fermentation to inhibit yeast proliferation after heating up; after the main fermentation is finished, the temperature reduction should not be too fast; use strains with strong diacetyl reduction ability; add high-foaming wine to speed up After the main fermentation, the temperature should not be lowered too fast.

6. Diacetyl rebound

After fermentation, diacetyl is qualified, but after low temperature storage or filtration, or after sterilization, the content of diacetyl increases, which is called diacetyl rebound.

The main reasons for diacetyl rebound are: the high residual amount of diacetyl precursors in beer, oxygen absorption after filtration causes diacetyl rebound after sterilization; the rebound of diacetyl caused by bacteria in the late fermentation; oxygen absorption after filtration makes yeast reproduce to produce α-acetyl lactic acid, which increases the diacetyl content after oxidation.

Solutions: reduce oxygen inhalation as much as possible when filtering; do not store the sake for a long time after filtering, and do not leave it overnight without a full tank; add antioxidants such as ascorbic acid or add glucose oxidase to eliminate dissolved oxygen in the sake; use carbon dioxide back pressure in the filling machine; use sake or deoxygenated water to induce froth when filling the sake to ensure complete exclusion of air from the bottle neck and avoid oxygen absorption in the beer.

7. Fermentation suspension phenomenon

The fermentation of fermented liquor is suspended, that is, the so-called "no sugar reduction".

The causes of this phenomenon include: insufficient wort nutrition, high oligosaccharide content, insufficient α-amino nitrogen, too high or too low acidity; strong yeast coagulation, resulting in early flocculation and precipitation; yeast degeneration and mutation resulting in no sugar reduction; yeast spontaneous mutation, resulting in respiration-deficient yeast.

Solution: If it is caused by strong coagulation of yeast, which causes early flocculation and precipitation. This can be done by increasing wort ventilation, adjusting fermentation temperature, and waiting for the sugar level to drop close to the final fermentation level before lowering the temperature to extend the high temperature period. However, it will improve the coagulation performance of yeast, and it is better to solve this phenomenon by using yeast strains with weaker isolation coagulation. If it is due to yeast degradation, a mutation occurs that causes no sugar reduction. It can be solved by using a new yeast strain. If it is caused by a spontaneous mutation of the yeast that produces a respiration-deficient yeast. It can be re-expanded from the original strain or replaced with a new strain. In addition, in the wort preparation process, we should strengthen the protein hydrolysis, appropriately reduce the protein decomposition temperature and extend the protein decomposition time; when mashing, we should appropriately adjust the mashing temperature, strengthen the low temperature section of hydrolysis, ensure sufficient mashing time, and adjust the mash pH value.

4, other beer fermentation technology

(A) pure draft beer brewing technology

Draft beer is strictly aseptic (non-heat sterilized) to ensure that there is no live yeast or other microorganisms in the liquor, with a shelf life of six months to a year, also known as cold sterilized beer. Draft beer is a new beer product that has been gradually developed in recent decades, with the goal of freshness, purity and crispness in the taste of beer. Due to the continuous improvement of cold sterilization technology, the production of draft beer is increasing and has become one of the hot spots of market competition in the beer industry. It is expected that draft beer will occupy an important position in the beer sales market in China in the next few years.

The quality requirements for draft beer are: to have the same biological and abiotic stability as "cooked beer"; to maintain the freshness of beer for a longer period of time (flavor stability); to have better aroma and taste, as well as good body appearance and foam performance; and to meet the required physical and chemical index requirements. That is, draft beer has the same quality requirements as cooked beer, except that it is not heat sterilized.

The main problem in the production of draft beer: Because of the lack of heat sterilization, the activity of protease A in the beer still exists, which has a greater impact on the foam of the beer, resulting in poor foam-holding properties of the beer.

Measurements of pure beer: Measurement of sucrose-converting enzyme activity in beer. The activity of sucrose convertase is generally destroyed in beer that has been pasteurized or instantly sterilized, and the presence or absence of sucrose convertase activity can determine whether it is a pure beer.

1. Raw beer production methods.

Raw beer production must be sterile or controlled throughout the production process, and finally enter the aseptic filtration combination system for aseptic filtration. Including compound deep aseptic filtration system and membrane aseptic filtration system. After aseptic filtration, it is required to basically remove yeast and all other microbial nutrient cells (aseptic filtration LRV≥7) to ensure the biological stability of pure draft beer.

(1) Microbial inhibition method Inorganic inhibitors or organic inhibitors (preservatives) are added to the liquor to avoid beer deterioration by inhibiting microbial reproduction and metabolism. Commonly used disinfectants include benzoic acid, sorbic acid, tragic acid, mycophenolate, lactic acid streptococcal peptide, etc.

(2) UV sterilization method Killing microorganisms by UV light to control the small amount of microorganisms in beer. Because the effect of UV sterilization is not ideal and may have an impact on the taste of beer, it is not used.

(3) Aseptic filtration method This method is commonly used for cold sterilization. After filtering by diatomaceous earth filter and fine filter, the beer enters the aseptic filtration combination system for aseptic filtration. Including compound deep aseptic filtration system and membrane type aseptic filtration system. After aseptic filtration, the yeast and all other microbial nutrient cells are basically removed (aseptic filtration LRV≥7) to ensure the biological stability of the draft beer.

2. Basic requirements for the production of draft beer:

(1) The key to pure brewing - beer yeast The production of pure draft beer is an organic combination of pure brewing and effective control of late contamination. The presence of any stray bacteria will affect the quality of the beer.

(2) Selecting a good base After fermentation and post-ripening, the beer should have good quality (including flavor, foam, abiotic stability and meeting the requirements of physical and chemical indexes). The production should be done carefully: good raw material, good selection of strains, strict production process and operation.

(3) Ensure that there are reliable aseptic production conditions Pure draft beer production is the result of effective control of stray bacteria in the production process, rather than the result of treatment by various means. Strict control of trash bacteria in the production process is the key to the production of pure draft beer, while aseptic filtration and aseptic filling are the auxiliary means of production. Therefore, the entire production process of beer should be as free or basically free from contamination by miscellaneous bacteria as possible in order to ensure the quality of pure draft beer and reduce the workload of post-processing.

(4) On the basis of strict control of microbial contamination in the previous process, the aseptic filtration carried out in the production of draft beer should meet the following requirements: the effectiveness of aseptic filtration, the removal rate of any microorganisms should meet the requirements, and will not affect the taste of beer, foam and other quality requirements; the selection of a reasonable combination of aseptic filtration, the general requirements should be in the order of deep filtration - surface filtration - membrane filtration combination, the pore size Choose: deep filtration 1 ~ 3 microns, surface filtration 0.8 ~ 1 micron, membrane filtration 0.45 ~ 0.65 microns. Two sets of filtration combinations should be configured to ensure normal production; with independent CIP and membrane regeneration systems.

(5) When packaging pure draft beer, the following basic requirements should be in place: the packaging container cleaning system (including bottles, cans, and draft beer kegs) should be clean and sterile; for the filling workshop, the filling machine can be placed in an airtight sterile room, with effective filtration of the indoor air and positive indoor-to-outdoor pressure of about 0.03 to 0.05 kPa; for the conveyor chain that conveys beer bottles, before the beer is filled and The part before sealing should use chain lubricant with disinfection effect, while the part of the conveyor chain in front of the filling machine should have a constant cleaning device to ensure the hygiene of the whole conveyor chain; the bottle washing machine of the draft beer filling line should use a single end in and out to prevent the dirty bottles at the incoming end from polluting the clean bottles at the outgoing end; the washed beer bottles should have an airtight shield in the process of conveying them to the filling machine to avoid pollution by dust, flying insects, etc. 3.

3. Microbiological management in the production process of pure draft beer

(1) Preparation of brewing sterile water

Treatment process.

Deep well water → softening treatment → sand filter → activated carbon filter → particle trapping filter → pre-filter → sterilization filter

For hard water should be softened first and remove large particle impurities before membrane filtration treatment. Water de-bacterization filter should be sterilized with steam before use, and the water network of production water should be cleaned and disinfected regularly. Microbiological control index of sterile water: total number of bacteria ≤ 10 / 100ml, yeast 0 / 100ml, anaerobic bacteria 0 / 100ml.

(2) Preparation of aseptic air

Sterile air is used for cold wort oxygenation and yeast expansion. Improper treatment of sterile air filtration will have an impact on microbial control in the production of pure draft beer, and the management of the sterile air filtration system must be strengthened. The preparation process of sterile air is as follows.

Compressed air → oil, water and trash particles removal → pre-filter → sterilization filter → key station sterilization sub-filter → sterile air

Microbial control index of sterile air: total number of bacteria ≤ 3 / 10 minutes, yeast 0 / 10 minutes, anaerobic bacteria 0 / 10 minutes.

(3) Preparation of sterile CO2

In the beer brewing process, CO2 is used for the addition of saison CO2, preparation of deoxygenated water, back pressure of saison tanks, etc. In the production of pure draft beer, CO2 is also treated aseptically, and the CO2 recovery pipeline is cleaned regularly by CIP, and the gas sterilization filter is steam sterilized before each use. The preparation process of sterile CO2 is as follows.

CO2 liquefaction storage tank → heating and gasification → pre-filter → de-bacterization filter → split point de-bacterization filter → sterile CO2 Microbial control index of sterile CO2: total number of bacteria ≤ 3 / 10 minutes, yeast 0 / 10 minutes, anaerobic bacteria 0 / 10 minutes.

(4) Treatment of steam for sterilization

The purpose of the treatment is to remove the particles brought in by steam, to prevent the destruction or blockage of the sterilization cartridge, and to extend the service life of the cartridge. Steam filtration generally uses microporous filter cartridges made of stainless steel and with a filtration precision of 1.0μm.

(5) Microbial control in filtration operation

①Avoiding contamination of the fermentation broth with miscellaneous bacteria is the basis of pure draft beer production.

(②CIP cleaning of the wine conveying pipeline, buffer tank, filter, diatomaceous earth (or perlite) addition tank and clearing tank before filtration.

③The sampling valve of the filtration system and clearing tank should be disassembled and cleaned regularly and strictly before each operation.

④Active elbows, pipe connections, hoses, sampling valves, tools, etc. should be soaked in disinfection solution when not in use.

⑤ The diatomaceous earth addition room should be separated independently and UV lamps should be installed for regular sterilization.

⑥After each operation, it should be cleaned with 0.1% hot acid, and the filtration system should be cleaned with 2.0% hot alkali every week.

⑦ Clear wine requirements.

Turbidity<0.5EBC unit; β-glucan <150mg/L; iodine reduction reaction <0.5. Total number of bacteria ≤50/100ml, yeast 0/100ml, anaerobic bacteria 0/100ml.

(6) Aseptic filtration of sake

Aseptic filtration is carried out by a 0.45μm membrane filter installed in front of the filling and capping machine, and the membrane filter should have a highly sensitive membrane integrity detection system. The cold and hot water used for the membrane filter should be pre-filtered through 20μm to process large particles before being used for the membrane filter.

(7) Aseptic filling

①The filling room should reach the clean requirement of 300,000 levels. The design, construction and sanitary disinfection of the clean room can refer to the GMP standard of the pharmaceutical industry.

②The clean room staff should wear clean clothes, and the number of people should be within 4 people. Avoid frequent entry and exit of personnel, and strict disinfection should be carried out when personnel enter and exit.

③Bottles for draft beer should be new bottles with good sanitary conditions (e.g. film-wrapped pallet bottles); sterile bottle caps suitable for use with draft beer should be used, and bottle cap storage hoppers should be installed with UV lamps for disinfection.

④The last wash water of bottle washing machine should be changed to hot water to rinse the bottles; the bottle delivery system from the exit end of bottle washing machine to the entrance of clean room should be installed with isolation cover and UV lamp, and the exit end should be hot disinfected for 1 hour; chain lubricant containing anti-bacterial ingredients and softening agent with water resistance and acid and alkali resistance should be used, and the conveying chain plate, water receiving plate, bottle guard bar, glass cover and chain bottom frame parts should be disinfected.

⑤ Before using the filling and capping machine, the surface of the equipment, the incoming and outgoing bottles should be cleaned, and the UV lamp should be turned on in advance for air disinfection. The filling and capping machine should be acid washed regularly every month to prevent scaling inside the machine.

4. Ensure reliable aseptic conditions in the production of draft beer

Strictly speaking, "the production of pure draft beer is the result of effective control of trash contamination during the production process, not the result of treatment by various means", and therefore cannot rely solely on end-of-line filtration and corresponding other treatments. In other words, the most important thing in the production process of draft beer is to strictly control the contamination of the production process, while the final aseptic filtration and aseptic filling are only auxiliary means to ensure and improve the quality of draft beer. For this reason, it is required that the whole process of beer production be as free or basically free of contamination by bacteria as possible. In the words of the Siping Kinsberg Brewery Group, the key to producing pure draft beer is to create a pure environment. In order to ensure the quality of the pure draft beer and to reduce the workload of aseptic filtration and aseptic packaging at a later stage, it is required that the trash bacteria should be less than 10/ml.

(1) Types of miscellaneous bacteria contamination in the beer production process.

① Primary and secondary contamination.

Primary contamination refers to the beer production process, from the time it can be contaminated microbial contact contamination occurs, this contamination is more harmful. Secondary contamination refers to contact contamination that occurs again after the beer has been aseptically processed, and occurs mainly in the clearing and packaging process. Secondary contamination is what must be strictly controlled in the production of pure draft beer.

②Cross-contamination and cumulative contamination.

Cross-contamination refers to mutual contamination caused by production equipment, production tools, the addition of yeast and other shared facilities contaminated by miscellaneous bacteria and insufficient disinfection and sterilization. Among them, the pollution of yeast is more harmful.

Cumulative contamination refers to the accumulation of contamination caused by the continuous occurrence of contamination in various processes during the production of beer. The amount of this contamination is serious, and the quality of beer is the most harmful.

③ Direct contamination and indirect contamination.

Direct contamination refers to direct contact with the product of raw and auxiliary materials, additives, equipment, pipelines and air and water sources containing miscellaneous bacteria on the product; indirect contamination refers to the contamination of items in direct contact with the product and contaminated, such as the human body, the environment, etc.

(2) production of pure draft beer, should also do the following aspects of work.

① First of all, we should do a good job with the product in direct contact with the air source, water and other materials of aseptic filtration and sterilization sterilization work to prevent direct contamination of the product and a pollution.

②Secondly, for the production processes of wort preparation, beer fermentation, aseptic filtration and packaging, the corresponding CIP and SIP systems should be configured separately and not shared as much as possible.

③The inner walls of containers, pipes, valves, etc. used in production should be polished. The Ra of the inner wall after polishing should be no less than 0.8 microns and as much as possible up to 0.5 microns.

④The whole beer production process should be carried out under closed, with positive pressure, and get good CIP washing and effective SIP disinfection and sterilization.

⑤ All kinds of raw materials, materials and preparations used when the beer products are in a cold state, including the addition of yeast, should be strictly controlled in aseptic conditions to ensure that no contamination by miscellaneous bacteria occurs.

(6) Microbiological testing means should be improved, corresponding microbiological testing points and testing systems should be determined, advanced testing methods and testing instruments should be used, and effective microbiological monitoring should be carried out throughout the process to ensure the conditions for aseptic production.

(II) Production technology of wheat beer

Wheat beer is a special type of beer brewed with wheat malt as the main raw material, using some malt, auxiliary materials (rice, etc.), adding hops, and using the above fermentation process, which is characterized by a refreshing, soft taste, high alcohol content, and good foam performance, similar to foreign pale beer or above fermented beer.

1. Production forms of wheat beer

There are three forms of wheat beer production as follows.

(1) top fermentation type Belongs to the traditional Ale (Ale) beer production method, with wheat malt, malt as raw materials, according to a certain saccharification process made of wort, inoculated with top yeast for fermentation at a higher temperature, after the end of fermentation with the skimming method to recover yeast, after a suitable time of maturation and storage made of wine, with the typical flavor of Ale beer.

(2) Mixed fermentation type The saccharification operation is the same as the above fermentation type, but two types of yeast (above yeast and below yeast) are used for fermentation at the same time, but the yeast is added at different times, i.e. the fermentation is first carried out at a higher temperature and with the above yeast, and after reaching a certain fermentation degree, the yeast is recovered in the same way as the above fermentation, and then transferred to the storage tank. Fermentation is carried out by adding the following yeast in the storage tank, and after a proper time of post-ripening, it is ready.

(3) Stage fermentation type Similar to the mixed fermentation type, that is, the wort made of wheat malt and malt is fermented at a higher temperature by adding the above yeast, and after the fermentation is finished, the above yeast is separated by a yeast centrifuge, then the above yeast is removed by instant sterilization and quickly cooled to the fermentation temperature of the following yeast, and the above wort and the following yeast are added for the second fermentation, after the post-ripening treatment. Foreign white beer is mainly produced by the above method.

2. Selection of wheat malt

Wheat with low protein content, low color and viscosity is generally selected to make wheat malt.

(1) The solubility of wheat malt is generally lower than that of barley malt, the coarse and fine powder leachate difference is high, the Kulpaha value is low, the protein dissolution is insufficient, and the decomposition of protein should be strengthened when saccharification.

(2) The anhydrous leaching rate of wheat malt without rough husk is about 5% higher than that of barley malt.

(3) The content of anthocyanin in wheat malt is low, and the washing water temperature can be increased to 80℃ (the washing water is first acidified).

(4) The higher glycoprotein content of wheat malt enables the brewed beer to have good foam performance and rich and long-lasting foam.

(5) Due to insufficient cell lysis, the high content of β-glucan and other hemicelluloses in small malt, the high viscosity of the wort made is easy to cause difficulties in wort filtration, and appropriate amounts of β-glucanase and pentosanase should be added during saccharification to reduce wort viscosity and speed up filtration.

(6) Higher protein content in wheat malt will cause difficulties in wort filtration and poor abiotic stability of beer, so wheat varieties with lower protein content should be used to prepare wheat malt as much as possible.

(7) Wort filtration should be done using a wort press as much as possible.

(8) Traditional wheat beer has a distinct ester flavor and sourness, while the flavor of wheat beer brewed with the following yeast low temperature fermentation does not change much.

(9) Adding silica gel to wheat beer before filtration can improve the clarity of the beer and make it easy to filter.

4. Process requirements

(1) Strengthen the decomposition of proteins in the saccharification stage The nitrogen content of wheat malt is higher than that of barley malt, and the solubility of wheat malt is lower than that of barley malt, the proportion of powdered grains is slightly lower (more than 80%), and the value of kulpaha is less than 40%, so the decomposition of proteins must be strengthened.

(2) The turbidity of wheat beer is high, and wort clarifying agent (carrageenan) can be added during wort boiling at an amount of 20-30mg/100L wort to improve wort clarity and speed up wort filtration.

(3) Strengthen the wort boiling, boiling intensity should reach 9-10%, boiling pH is 5.2-5.4. You can also add appropriate amount of CaCl2, which is conducive to protein flocculation and precipitation.

(4) Adopt low-temperature fermentation process, discharge yeast in time after boosting to reduce yeast autolysis, and discharge yeast every 2 days or so during the storage period. 0℃ below the storage time is appropriately longer to facilitate protein and protein-polyphenol substance west out.

(5) Add protease such as enzyme clear or papain to further decompose protein when filtering, the amount of addition should be determined according to a small test. Adding too much will make the beer taste lighter and the foam performance worse, and it will also cause the beer to be cloudy (because it is also protein itself).

(6) Quickly cool down the fermentation broth before filtering, so that the temperature of the fermentation broth reaches below -1℃ to promote the precipitation of proteins.

(7) You can also add an appropriate amount of edible tannins to precipitate proteins before filtration, and the amount added is generally about 20mg/100L of beer, which helps prevent beer cloudiness and avoid difficulties in filtering beer.

(3) Low-alcohol, alcohol-free beer production technology

Low-alcohol beer refers to special beer with a lower alcohol volume fraction value than normal beer, such as alcohol-free beer, low-calorie beer, etc. Alcohol-free beer refers to special beer that has undergone the normal beer production process but has an alcohol volume fraction of less than 0.5%. Alcohol-free beer is very suitable for social occasions because of its low alcohol content, and also for some people who should not drink alcohol, such as women, drivers, athletes, teenagers, children, people with alcohol allergies and other consumer groups. It is understood that the first non-alcoholic beer launched by Switzerland, in the United States, Germany, Britain, Japan and other countries have been produced one after another, and has been a great development. Domestic Yanjing and other beer production enterprises have begun to use low-temperature vacuum distillation technology to produce alcohol-free beer.

The key to the production of low-alcohol beer is to require low alcohol content but not less unique flavor of beer, and other quality characteristics should also be ensured.

The production process for low-alcohol beer can be broadly divided into two categories.

One type is to control the amount of alcohol produced during the fermentation of the beer to be within the required standard range, such as the Lucian yeast method, the Pasteur patent method, and the high-temperature saccharification method. Alcohol-free beer can be produced using yeast that has undergone induced mutation, which can reduce alcohol during fermentation (transformed into esters or organic acids, etc.) or basically produce no alcohol, allowing normal fermentation of wort without undesirable flavors and harmful ingredients, with alcohol volume fraction ≤ 0.5% in the fermented mature beer.

The other type is to remove alcohol from normally fermented beer by various means to meet the standard requirements, such as reduced pressure evaporation method, reverse osmosis method, dialysis method, etc.

The advantages of the alcohol removal method are.

(1) The amount of alcohol removed can be controlled at will, and alcohol-free beer can be produced.

(2) The fermentation process of saccharification does not need to be changed, and only post-fermentation treatment is required.

Disadvantages of the alcohol removal method are.

(1) A large amount of capital needs to be invested in alcohol removal equipment.

(2) Additional processing costs and time are required.

(3) The beer flavor is lost during the treatment process.

(4) Improper treatment can easily cause secondary contamination.

The advantages of the restricted fermentation method are.

(1) No additional investment in equipment is required.

(2) Simple and low cost production process.

(3) less flavor loss.

The disadvantages of the restricted fermentation method are.

(1) saccharification or fermentation process changes and process control requirements are high.

(2) Improper control can affect the taste and stability of the beer.

Both types of production processes are used. The restricted fermentation method is more economical and practical for the production of low-alcohol beer, while the low-temperature vacuum distillation method is more costly, and the application of membrane technology opens up new avenues for efficient, energy-saving and environmentally friendly alcohol-free beer production.

1. Introduction of methods for producing low-alcohol beer by restricted fermentation.

(1) Dilution method

The normal concentration of wort is diluted to a lower concentration for fermentation, or the normal wort can be fermented and diluted to the required concentration to produce low-alcohol beer. If the dilution is too high, the beer flavor is diluted at the same time, causing the beer to taste weak.

(2) Low-temperature leaching and saccharification method

After the malt is crushed and soaked in hot water at a temperature lower than 60°C, the starch in the malt will not be pasteurized and decomposed under these conditions, and no fermentable sugars will be produced, and the leachate will contain only a small amount of the sugar from the malt. Fermentation of the wort treated by this saccharification method produces a lower content of alcohol.

(3) Termination of fermentation method

When the beer is fermented to the required alcohol content, the fermentation is stopped by quickly lowering the temperature and simultaneously separating the yeast from the fermentation broth. This process produces beer with a sweet taste, and diacetyl reduction is difficult to complete.

(4) Pasteurized patent method

This process combines high concentration fermentation and low concentration fermentation methods cleverly, overcoming both the shortcomings of low alcohol beer produced by low concentration fermentation methods in terms of light taste and high alcohol content by high concentration fermentation methods. The flavor of low-alcohol beer produced by this method is better, and the production process is simple and easy to control. This process can produce low-alcohol beer with alcohol content from 0.9% to 2.4%.

(5) Spent lees method

The molasses waste wort is then soaked, acid decomposed and boiled to produce a lower concentration of wort. To ensure the proper flavor of wort, 40% to 60% of wort produced by the low temperature leaching method can also be added. This wort fermentation produces a lower alcohol content. The disadvantage of this process is that it is tedious to operate.

(6) Road yeast method

Specialized Lu's yeast is used to ferment normal wort. Since this yeast can only ferment fructose, glucose and sucrose, which account for about 15% of the total sugar content in wort, and cannot ferment maltose, only a small amount of alcohol can be produced. However, the disadvantage is that the low-alcohol beer produced by this process has a sweet taste due to the large amount of maltose, and the beer is less biostable.

(7) High-temperature saccharification method

By using a higher saccharification temperature, the process of β-amylase decomposition of starch is skipped to avoid the production of large amounts of maltose, but the liquefaction is complete to prevent excessive dextrin residues from affecting the stability of the beer. The wort produced by this process can only ferment 25% to 30% of the normal sugar during fermentation by yeast, and the alcohol content can be completely controlled to below 1.5%. The key to this process is the precise control of saccharification. Proper control of the saccharification process can completely ensure that the beer has both the right fermentation level and a good beer flavor and stability. The disadvantage is that the saccharification operation is more demanding.

(8) Immobilized yeast fermentation method

Using specific yeast immobilized to a certain carrier, the wort flows slowly through the immobilized yeast column within 5 to 20 h. The alcohol formation is accurately monitored and regulated by low temperature and adjusted flow rate to produce alcohol-free beer that meets the requirements. While controlling alcohol formation, fermentation by-products and taste substances can still be produced, and the produced alcohol-free beer can meet the quality requirements with low alcohol loss and environmental protection, which has good potential for development.

2. Introduction of alcohol-free beer method by alcohol removal

(1) low-temperature vacuum evaporation (distillation) method

This method is to evaporate the ethanol in the normal fermented beer by reduced pressure evaporation or distillation, and add the right amount of water to achieve the quality requirements of alcohol-free beer; or the alcohol can be evaporated or distilled, and then mixed with a certain amount of beer containing low alcohol, so that the flavor of the mixed beer is close to normal beer.

The method requires distillation at low pressure (4 to 20 kPa absolute pressure), low temperature (30 to 55 ℃), so that the alcohol volume fraction will be to 0.5% or less. The methods used are vacuum distillation method, vacuum evaporation method and vacuum centrifugal evaporation method. Among them, the evaporation method is more effective in use.

(2) Membrane separation method

Membrane separation method is to make the beer flow through the membrane made of organic or inorganic materials to achieve the purpose of alcohol removal. The commonly used methods are reverse osmosis and dialysis.

Reverse osmosis method of alcohol removal is divided into three stages: concentration, secondary filtration and replenishment. Concentration stage: 2.2L of leachate is produced per 100 liters of beer by membrane filtration, and the alcohol content and concentration of residual beer increases. Secondary filtration stage: The roasted leachate from the beer is replenished with completely desalted water until the required alcohol content is reached in the concentrate. Replenishment stage: The concentrate is replenished with water to the original amount of beer and the alcohol content is reduced to less than 0.5%, and the beer is also replenished with CO2, as the CO2 content in the beer is very low through reverse osmosis and replenishment of water.

The membrane for dialysis is made of thin-walled hollow fibers with very small pore sizes. The alcohol in the beer permeates through the membrane to the other side of the membrane, while the macromolecules in the beer are trapped. As the dialysis process proceeds, the alcohol content in the leachate gradually increases and the alcohol content in the beer gradually decreases. When the alcohol in the exudate is slowly removed by continuous vacuum distillation, the alcoholic liquor in the beer can reach the requirement.