How does alcohol become acetic acid?

Vinegar is a kind of acidic condiment made by our laboring people in the long-term production practice. It can improve appetite, help digestion, indispensable in people's dietary life. Vinegar also has certain uses in Chinese medicine. There are many varieties of vinegar produced all over the country. The famous Shanxi aged vinegar, Zhenjiang balsamic vinegar, Sichuan bran vinegar, Northeast white vinegar, Jiangsu, Zhejiang rose rice vinegar, Fujian red vinegar and so on are the representative varieties of vinegar. According to the processing method, vinegar can be divided into three categories: synthetic vinegar, brewing vinegar and reconstituted vinegar. Among them, the one with the largest production and the closest relationship with us is brewing vinegar, which is made from grain and other starch as raw material, through microbial brewing, saccharification, alcoholic fermentation, acetic acid fermentation and other stages of brewing. Its main components in addition to acetic acid (3% to 5%), but also contains a variety of amino acids, organic acids, sugars, vitamins, alcohols and esters and other nutrients and flavor components, with a unique color, aroma and taste. It is not only a good flavor, long-term consumption of health is also very beneficial.

1.1.1 Production of raw materials

The main raw materials used in the production of vinegar are: potatoes such as sweet potatoes, potatoes, etc.; grains and cereals such as corn, rice, etc.; food processing scraps such as broken rice, bran, bran, etc.; fruits and vegetables such as black currants, grapes, carrots, etc.; wild plants such as acorns, chrysanthemums, etc.; and others such as sour fruit wine, sour beer, molasses and so on.

Production of vinegar in addition to the above main raw materials, but also need loose materials such as grain husk, corn cobs, etc., so that the fermentation material permeability is good, aerobic microorganisms can grow well.

1.1.2 Brewing microorganisms

The traditional process of brewing vinegar is to use the wild fungus in nature to make music and fermentation, so it involves many kinds of microorganisms. The new method of vinegar are using artificially selected pure culture strains of bacteria to make music, alcohol fermentation and acetic acid fermentation, thus the fermentation cycle is short and the utilization rate of raw materials is high.

1) Starch liquefaction, saccharification microorganisms

Starch liquefaction, saccharification microorganisms can produce amylase, saccharification enzyme. There are many microorganisms that make starch liquefaction and saccharification, and the one suitable for vinegar making is mainly Aspergillus. Commonly used Aspergillus species are:

Sweet potato Aspergillus AS 3.324, named because it is suitable for sweet potato raw material saccharification, the growth of the fungus is well adapted, easy to cultivate, strong tannin enzyme vitality, suitable for sweet potatoes and wild plants, etc. to make vinegar;

Dongjiu No. 1 It is a mutant of AS 3.758, the cultivation of which requires a higher humidity and lower temperature, the application of this fungus to make vinegar more in Shanghai;

This fungus has been used to make vinegar more;

There are many microorganisms to make starch liquefaction and saccharification.

Aspergillus niger AS 3.4309(UV-11) The bacterium has strong saccharification ability, pure enzyme system, and the optimal culture temperature is 32℃. When making song, the mycelium grows slowly in the early stage, and when conidia appear, the mycelium spreads rapidly;

Aspergillus niger AS 3.758 is a saccharification type amylase strain whose saccharification power is extremely strong and acid resistance is high, which is selected and bred in thousands of species of Aspergillus niger in Japan. The mycelium is black to black-brown. The spores are blackish brown when mature. It can assimilate nitrate, and its ability to produce acid is very strong. The suitability of the raw material is also relatively strong.

In addition, there are Aspergillus oryzae strains: HU Brewing 3.040, HU Brewing 3.042 (AS 3.951), AS 3.863 and so on. Aspergillus flavus strains: AS 3.800, AS 3.384 and so on.

2) Alcohol fermentation microorganisms

Production is generally used in the production of yeast in the yeast genus Cysticercus subphylum, but different strains of yeast, its fermentation ability is different, resulting in different flavors and aromas. 1300 yeast is commonly used in the northern region, and Shanghai balsamic vinegar uses Gongnong 501 yellow wine yeast. k yeast is suitable for making common vinegar from sorghum, rice, sweet potato, etc. AS 2.109, AS 2.399 are suitable for starchy raw materials, while AS 2.1189, AS 2.1190 are suitable for molasses raw materials.

3) Microorganisms of acetic acid fermentation

① Selection of acetic acid bacteria

Acetic acid bacteria is the main strain of acetic acid fermentation. Acetic acid bacteria have the ability to oxidize alcohol to produce acetic acid, its form of long rod or short rod-shaped cells, alone, in pairs or arranged in chains. Does not form spores, Gram staining young bacteria negative, old bacteria are unstable, aerobic, like to grow in the medium containing sugar and yeast paste. The optimal temperature for its growth of 28 ~ 32 ℃, the optimal pH value of 3.5 ~ 6.5.

Vinegar factory selection of acetic acid bacteria standards: fast oxidation of alcohol, acid resistance, no longer decompose acetic acid products, good flavor strains. At present, domestic and foreign production in the commonly used acetic acid bacteria are:

Orlean vinegar bacillus (A. orleanense) It is the main strain of vinegar production with wine in the Irish region of France. The optimum temperature for growth is 30°C. The bacteria can produce a small amount of ester, acid production capacity is weak, but acid resistance is strong.

A. schutzenbachii is a famous fast-brewing vinegar strain in foreign countries, and it is also one of the more important strains in vinegar industry. The optimum temperature for growth in liquid is 25~27.5℃, the optimum temperature for solid culture is 28~30℃, and the highest growth temperature is 37℃. The bacterium produces acid up to 11.5%. It has no oxidizing effect on acetic acid.

Acetobacter rancens is one of the common strains of vinegar in China. The bacterium forms bacterial film at the liquid surface and rises along the container wall, and the liquid under the bacterial film is not turbid. Generally it can produce acid 6~8%, and some strains by-produce 2% gluconic acid, and can further oxidize acetic acid into carbon dioxide and water.

AS 1.41 Acetic acid bacteria It belongs to malodorous acetic acid bacteria, is one of the commonly used strains of vinegar in China. The cells of this bacterium are rod-shaped, often arranged in chains, and the size of a single cell is (0.3~0.4)μm×(1~2)μm, non-motile and non-budding. Under adverse environmental conditions, the cells would elongate into linear, rod-shaped or tubular expansion. Plate culture colonies bulge, the surface is smooth, the colony is grayish white, liquid culture is the formation of bacterial film. The suitable temperature for the growth of the bacterium is 28~30℃, the most suitable temperature for the generation of acetic acid is 28~33℃, the most suitable PH3.5~6.0, and the tolerant alcohol concentration is 8% (volume fraction). The highest production of acetic acid is 7~9%, and the production of gluconic acid is weak. Can oxidize and decompose acetic acid into carbon dioxide and water.

Shanghai Brewing 1.01 Acetic Acid Bacteria It is isolated from Dandong Quick Brewing Vinegar, and is one of the commonly used strains in vinegar factories in China. The cells of this bacterium are rod-shaped, often arranged in chains, the bacterium is non-motile and does not form spores. In the culture liquid containing alcohol, it often grows on the surface and forms a thin layer of light greenish gray bacterial film. Under adverse conditions, the cells will elongate and become linear or rod-shaped, some of which are expanded and branched. The bacterium by the conversion rate of alcohol-generated acetic acid is as high as 93 ~ 95% on average.

② Acetic acid bacteria culture and preservation

a slant test tube medium

The following are two examples of slant test tube medium:

Alcohol (6%) 100ml glucose 0.3g yeast paste 1g CaCO3 1.5g agar 2.5g;

glucose 1g alcohol 2ml calcium carbonate (CaCO3) 1.5g. Yeast paste 1g Agar 2.5g Water 100ml.

PH value natural (various ingredients are first heated and dissolved before heating the alcohol).

b Acetic acid bacteria culture and preservation

Acetic acid bacteria after slant inoculation placed in 30 ~ 32 ℃ thermostat incubator culture 48h. Acetic acid bacteria because there are no spores, so it is easy to be killed by their own produced by the acid. In acetic acid bacteria, especially can produce aroma ester of the strain every ten days that is dead, so it is advisable to keep in 0 ~ 4 ℃ refrigerator standby. Because the medium has added calcium carbonate to neutralize the acid produced, so the preservation time is longer.

1.1.3 Solid-state method of vinegar production

Acetobacteria grow and multiply under sufficient supply of oxygen and oxidize the ethanol in the substrate to acetic acid, which is a bio-oxidation process, and the total reaction formula is: C2H5OH+O2=CH3COOH+H2O

1) Acetic acid strain preparation process

Slant original seed→slant (30~32℃, 48h)→triangular bottle liquid strain (first-class seed 30~32℃, oscillation 24h)→seed tank liquid strain (second-class seed)→(30~32℃, aeration culture 22~24h)→acetic acid bacteria seed

2) Process

Bran Quatre, yeast

↓

Dried potatoes (or crushed rice, sorghum and so on) ) → crushed → add bran, grain bran mix → moistening → steaming material → cooling → inoculation → into the tank saccharification and fermentation → mixing chaff inoculation → acetic acid fermentation → turn over the spirits → add salt and ripening → drenching vinegar → storage of aged vinegar → blending → sterilization → packaging → finished product

↑

Acetobacteria

3) Production process

① Raw materials proportioning and processing

Sweet potatoes or broken rice, Sorghum, etc. 100kg, 80kg of fine grain bran, 120kg of bran, 400kg of water, 50kg of bran, 50kg of huller, 40kg of acetic acid bacteria seeds, salt 3.75~7.5kg (more in summer and less in winter).

The dried potatoes or crushed rice and other crushed, plus bran and fine grain husk mixing, add water to moisten the material to normal pressure steaming 1h or at 0.15MPa pressure steaming 40min, out of the pot cooled to 30~40 ℃.

② Fermentation

After the raw materials are cooled down, mix in bran and brewer's yeast, and make up water appropriately, so that the moisture of grains reaches 60%~66%. The temperature of the fermentation tank is 24~28℃, and the room temperature is about 25~28℃. Into the tank the next day, the temperature rises to 38 ~ 40 ℃, should be the first inverted cylinder turning spirits, and then cover tightly to maintain the temperature of spirits 30 ~ 34 ℃ for saccharification and alcoholic fermentation. Into the cylinder after 5 ~ 7d alcohol fermentation is basically over, grains can contain alcohol 7% ~ 8%, this time mixed into the huller and acetic acid bacteria seeds, while inverting the cylinder to turn over the grains, and then turn over the grains once a day, the temperature is maintained at 37 ~ 39 ℃. About 12d acetic acid fermentation, grains temperature began to fall, acetic acid content of 7.0% ~ 7.5%, the basic end of acetic acid fermentation. At this time, the surface of the grains should be added salt. Generally, each cylinder of vinegar grains in summer add salt 3kg, winter add salt 1.5kg, mix well and then put two days, and then after 2d after the vinegar grains can be mature vinegar.

③The vinegar drenching

The vinegar drenching process adopts three sets of circulation method. First soak the mature vinegar grains with two vinegar for 20~24h, and dripping out is head vinegar, and the remaining head dregs are soaked with three vinegars, and dripping out is two vinegars, and the two dregs in the tank are soaked with water again, and dripping out is three vinegars. If the head drenched vinegar set head drenched vinegar for old vinegar; two drenched vinegar set two drenched vinegar 3 times for double vinegar, better quality than general single drenched vinegar.

④ Aging and smoked vinegar

Aging is the process of storing and maturing vinegar after fermentation of acetic acid to improve its flavor. There are two methods of aging, one is aging of vinegar grains, which is to compact mature vinegar grains and cover them tightly, and then directly pour vinegar after several months of sealing. Or use this method to store the vinegar grains, and then pour vinegar on the factory during the peak season. The other is vinegar liquid aging, i.e. dripping vinegar when the vinegar grains are ripe, and then the vinegar liquid is stored in tanks or cans for 1~2 months, which can get the aged vinegar with mellow flavor and bright color. Sometimes, in order to improve the product quality and flavor, some of the vinegar grains are heated to 70~80℃ by fire, and then dripping vinegar after 24h, which is called smoked vinegar.

⑤ Matching and sterilizing

The aged vinegar or the newly drenched head vinegar are still semi-finished products, and the head vinegar enters the clarifying pool to precipitate, adjust its concentration and composition, and make it conform to the quality standard. Except for the products of present sale and high-grade vinegar, generally it should be packed after adding 0.1% sodium benzoate preservative. The vinegar liquid of aged vinegar or new shower should be maintained at 85~90℃ for 50min to sterilize, but it should be rapidly cooled down after sterilization before leaving the factory. Generally the acid content of first grade vinegar is 5.0%, and the acid content of second grade vinegar is 3.5%.

1.1.4 Enzymatic liquefaction ventilation reflux vinegar

1) Characteristics of enzymatic liquefaction ventilation reflux vinegar

Enzymatic liquefaction ventilation reflux new process is a new vinegar making process which utilizes the natural ventilation and reflux of vinegar instead of pouring spirits. The characteristics of this method are as follows: α-amylase preparation liquefies the starch of raw materials and then sweeten them with bran, which improves the utilization rate of raw materials; the fermentation process of liquid alcohol fermentation and solid acetic acid fermentation is adopted; ventilation holes are opened on the wall of the acetic acid fermentation pool near the bottom of the false bottom, so as to let the air enter naturally and make use of the looseness of solid acetic acid grains to make the acetic acid bacteria get enough oxygen, so that all the grains of vinegar can be fermented uniformly; and the vinegar juice with lower temperature is accumulated under the false bottom, so as to make use of the natural ventilation and reflux instead of inverted grains. The lower temperature of the vinegar juice accumulated under the false bottom, regular reflux spray on the vinegar spirits to reduce the vinegar temperature spirits to regulate the fermentation temperature, to ensure that the fermentation is carried out at the appropriate temperature. → Altar filling → Finished product. ↑ ↑ ↑

↑ ↑ mother liquor (bran, huller, acetic acid bacteria seeds)

Salt

3) Production process

① Ingredients

1,200kg of broken rice, 1,400kg of bran, 1,650kg of huller, 1.2kg of sodium carbonate, 2.4kg of calcium chloride, 3.9kg of a-amylase in terms of 130 enzyme vitality units per gram of broken rice, 60kg of bran extract, 3.9kg of a-amylase per gram of broken rice, 3.9kg of a-amylase per gram of broken rice. kg, 60 kg of bran, 500 kg of brewer's mother, 200 kg of acetic acid bacteria seeds, salt 100 kg, 3250 kg of water (with fermentation mash).

② Water milling and pulping

Soak the broken rice to make the grains swell fully, send the ratio of rice and water 1:1.5 to the mill, grind it into a fine slurry of 70 mesh or more. Make the concentration of the pulverized slurry at 20%~23%, adjust it to pH 6.2~6.4 with sodium carbonate, add calcium chloride and α-amylase, and then send it to the saccharification pot.

③ Liquefaction and saccharification

Powder mash should be stirred and heated in the liquefaction pot, maintained at 85~92 ℃ for 10~15min, with iodine solution detection of brownish-yellow color indicates that the end point of liquefaction has been reached, and then warm up to 100 ℃ and maintain for l0min to achieve the purpose of sterilization and deactivation of the enzyme, and then send it to the saccharification pot. The liquefied mash is cooled to 60 ~ 65 ℃ when adding bran, insulation saccharification 35min, to be sugar liquid cooling to about 30 ℃, sent to the alcoholic fermentation vessel.

④ Alcoholic fermentation

Dilute the sugar solution with water to 7.5~8.0′Bx, adjust the pH to 4.2~4.4 to access the mother liquor, and carry out the alcoholic fermentation for 70h at 30~33℃, resulting in the mash containing about 8.5% of alcohol, with an acidity of 0.3~0.4. Then the mash was sent to the acetic acid fermentation tank.

⑤ Acetic acid fermentation

The wine mash is mixed with huller, bran and acetic acid bacterial strains, and sent to the fermenter with a false bottom and a flat cover. Into the pool temperature 35 ~ 38 ℃ is appropriate, and the middle layer of vinegar spirits temperature is lower, into the pool 24h for a loose spirits, the top and middle of the vinegar with as much as possible loose uniform, so that the temperature is consistent.

When the product temperature rises to 40 ℃ for vinegar reflux, that is, from the bottom of the false release part of the vinegar, and then splashed back to the surface of the spirits of vinegar, general reflux 6 times a day, during the fermentation period **** reflux 120~130 times, so that the temperature of the spirits is lowered. Acetic acid fermentation temperature can be controlled at 42~44℃ in the early stage and 36~38℃ in the late stage. After 20~25d acetic acid fermentation, vinaigrette acid content of 6.5%~7.0%, the basic end of fermentation. The end of acetic acid fermentation, in order to avoid acetic acid is oxidized into carbon dioxide and water, should be added in time to salt to inhibit the oxidation of acetic acid bacteria. The method is to put the salt on the surface of the vinegar grains, and use the vinegar juice reflux to dissolve the salt so that it penetrates into the vinegar grains. Vinegar drenching is still carried out in the acetic acid fermentation pool. Then pouring vinegar spirits with second vinegar, the bottom of the pool continues to collect vinegar juice, when the collected vinegar juice acid content drops to 5%, stop pouring vinegar. Previously collected for the first vinegar. Then pour three vinegars on the top, collect two vinegars from the bottom of the pool, and finally add water on the top and collect three vinegars on the bottom. Two vinegar and three vinegar *** drenching vinegar recycling.

6 Sterilization and blending

Sterilization is to kill the microorganisms in the aged vinegar or new drenching vinegar by heating; destroy the residual enzymes; and make the vinegar's composition basically fixed. Meanwhile, after the heating treatment, the vinegar has stronger aroma and more harmonious flavor.

Sterilized vinegar should be cooled quickly and blended according to the quality standard.

1.1.5 Liquid deep fermentation vinegar

Liquid deep fermentation vinegar is the method of producing vinegar through liquid deep fermentation using fermentation tank, usually the starchy raw materials are liquefied, saccharified and then made into wine mash or liquor first, and then acetic acid fermentation is completed in the fermentation tank. Liquid deep fermentation method of vinegar has the advantages of high degree of mechanization, good operation hygiene, high utilization rate of raw materials (up to 65-70%), short production cycle and stable quality of products. The disadvantage is that the flavor of vinegar is poor.

1) Process

Bran, mother of wine, acetic acid bacteria

↓ ↓ ↓

Crushed rice → soaking → grinding → pulping → liquefaction → saccharification → alcoholic fermentation → wine mash → acetic acid fermentation → acetate mash → filtration → blending → sterilization → aged vinegar → finished products

2) Production

Deeply fermented vinegar in the process of the liquid to the alcohol fermentation Until the process is the same as enzyme liquefaction ventilated reflux vinegar, the difference is that from the beginning of acetic acid fermentation, a larger fermentation tank is used for liquid deep fermentation, and it needs to be aerated and stirred, and the acetic acid bacterial seed is liquid, i.e. the mother of vinegar.

The temperature of acetic acid deep liquid fermentation is 32~35℃, the ventilation is 1:0.13/min in the first period; 1:0.17/min in the middle period; 1:0.13/min in the later period. the tank pressure is maintained at 0.03MPa. continuous stirring. Acetic acid fermentation cycle for 65 ~ 72h. Determined by the alcohol, residual sugar is very little, the determination of acidity is no longer increased that the end of acetic acid fermentation.

Liquid deep fermentation of vinegar can also be used semi-continuous method, that is, when the acetic acid fermentation is mature, take out one-third of the mature mash, plus one-third of the mash to continue to ferment, so every 20~22h repeat. At present, this method is mostly used in the production.