Overview: beer yeast is crucial in beer brewing.
Due to the influence of many environmental factors in the brewing process, some yeast will die and even autolysis will occur.
When there is more than 5% beer yeast autolysis in beer, beer will produce obvious yeast taste, bitterness and astringency, accompanied by other quality problems.
Autolytic yeasts are all dead aging yeasts. In actual brewing, it is impossible to completely prevent autolysis of yeast cells, but only to control the limits of autolysis of yeast cells.
Let's talk about the influence of environmental factors on yeast death and autolysis.
1. Wort wort oxygen, culture temperature and other conditions under certain conditions, the nutritional components of wort are very important to the metabolism of beer yeast. Α-in wort-
Amino nitrogen, fermentable sugar, pH value, inorganic ions and auxin and other nutrients are unreasonable, which will lead to yeast nutrition deficiency, slow metabolism and yeast aging, thus causing the possibility of yeast death and autolysis.
For example, the cold coagulation of wort is not completely precipitated, and the fermentation will inevitably hinder the reproduction and metabolism of yeast, reduce the activity of yeast, and make yeast cells aging, death and autolysis.
2. The content of zinc ions in inorganic ion wort shall not be less than 0. 25 mg/L, but shall not exceed 2 mg/L.
If the content of zinc ion is insufficient, the activity of intracellular enzymes such as alcohol dehydrogenase will obviously decrease, causing slow Yeast Proliferation and slow fermentation speed;
If the concentration of zinc ion is too high, it can promote the growth and metabolism of yeast, but yeast is easy to age and autolysis. The content of copper ion in wort is higher than 0.
Lppm, easy to mutagenize yeast, inhibit the activity of the enzyme.
Lead ions, two valence tin ions, six valence chromium ions and other heavy metal ions, toxic to yeast, will make beer yeast lose activity. The content of iron ions in wort is higher than 1. 0 mg/L.
It will also make yeast premature aging and increase the probability of death and autolysis.
Nitrite ions have strong toxicity to yeast cells, making beer yeast inactive.
Fluoride ions and nitrate ions will also change yeast inheritance, inhibit fermentation and yeast growth, and silicon oxide ions combine with proteins to form silica turbidity, forming micelles during fermentation and adsorbing on the yeast surface, reduce the metabolic capacity of yeast.
When the content of available phosphorus in wort is insufficient, the whole life process of beer yeast will be adversely affected.
3. Dissolved oxygen when the dissolved oxygen in the wort is insufficient, the proliferation rate of beer yeast decreases, and the new robust beer yeast decreases, which is easy to cause the aging and death of yeast cells.
When preserving yeast in Hanson tank or beer yeast storage tank, yeast exposure to oxygen may aggravate yeast death and autolysis.
4. Fermentation conditions the temperature of the fermentation broth is high and low, and the temperature rise and pressure rise in the reduction period are too late.
Will promote the degradation of beer yeast, increase mortality.
After the fermentation and diacetyl reduction, the beer yeast at the bottom of the conical tank should be discharged in time. If the discharge is not clean, the bottom is difficult to cool down, and the temperature rises, which is easy to cause yeast death and autolysis. Yeast mud without washing (In traditional fermentation)
Directly used in other conical tanks to grow yeast will inevitably bring some aging and dead yeast and increase the chance of autolysis.
5. Temperature, under low temperature conditions, yeast can also autolysis, but the autolysis speed is slow.
With the increase of temperature, the autolysis of beer yeast cells increased.
Increasing the fermentation temperature can accelerate the metabolism of yeast and shorten the fermentation time, but it is easy to increase the amount of harmful byproducts and accelerate the aging of beer yeast.
The design of conical tank and yeast storage tank is improper, that is, there is no cooling system or heat preservation device at the bottom, and the temperature of beer yeast deposited at the bottom is 3 ~ 6 degrees Celsius, increased the mortality of yeast.
6. Pressure fermentation liquid sealing pressure is too high, some yeast cells will die.
When yeast is recycled and added, the pressure difference changes too much, which will cause the burst of yeast cell wall and increase the mortality rate of yeast.
7. The amount of yeast added in the breeding tank or fermentation tank is too high (Greater than 28. 00 x 106/ml)
The α-amino nitrogen in wort is rapidly assimilated, which will cause relatively few yeast reproduction and growth generations, I . e. the concentration of newly added yeast is too low, the later stage lacks nutrition, and yeast is easy to age and die.
If autolyzed yeast is inoculated again, it will cause a vicious circle.
8. The soaking of wild yeast and miscellaneous bacteria in the fermentation broth of miscellaneous bacteria will inevitably hurt beer yeast and show a higher mortality rate.
9. The high concentration of hops added to hop Wort will also affect yeast activity.
10. Enzyme preparation when adding enzyme preparation to the fermentation broth, the yeast usage generation should not be too high, because enzyme preparation will promote the dissolution of yeast cells, resulting in increased mortality.
Therefore, the use of enzyme preparation must be careful, so that the addition amount is accurate, the addition time is reasonable, and the quality of enzyme preparation is high.
Beer yeast can secrete a variety of autolysin, and the most suitable PH for these autolysin is 6 ~ 8.
Too high or too low PH of fermentation broth is not conducive to the normal growth and fermentation of yeast.
11. Flushing time: after sterilization with chlorine dioxide or hydrogen peroxide in breeding tanks, conical tanks and storage tanks, the Flushing time with clear water is too short (Within 15 minutes)
Chloride ion concentration will exceed 100 mg/l, which can make beer yeast premature aging. Therefore, washing with clear water after sterilization should take more than 40 minutes.
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