About Fermentation of Lagers

     Cooled wort to which yeast has been added is subjected to intense fermentation by the yeast, which continuously reduces its sugar content and produces a certain amount of CO2, alcohol and by-products such as aldehydes, esters, acids and higher alcohols and other metabolites, a process known as saccharide reduction.

       In the pre-fermentation period, the rate of sugar reduction is not exactly the same every day, the rate of sugar reduction is relatively fast during the main fermentation period, and the rate of sugar reduction is a little slower in the period of time before the start and termination of fermentation.

       Sometimes during the main fermentation the sugar drop is very low, less than 1°P per day, an abnormality that affects the turnover of the fermentation equipment and the yield and quality of the beer. Generally speaking, there are the following reasons for the slow rate of sugar reduction:

1. wort composition

(1) The wort contains insufficient amount of fermentable sugars such as disaccharides and monosaccharides below malt trisaccharides, and the amount of dextrins and polysaccharides is on the high side, but the reduction of total leachate is not obvious.

(2) The content of ɑ-amino nitrogen in wort is too low, which makes the yeast multiply slowly and the number of newborn cells is low, resulting in a slow rate of sugar reduction.

(3) The amount of dissolved oxygen contained in wort is too low, which affects the reproduction rate of yeast.

(4) The wort does not contain enough purines and pyridines, which slow down the yeast fermentation of the wort even though they are not needed for yeast growth.

2. Yeast quality or reproduction

(1) Bad yeast strains with very poor fermentation performance.

(2) The number of yeast generations used is too high, the proportion of senescent yeast is high, and the mortality rate of yeast is also high.

(3) Yeast senescence, low germination rate, poor reproductive performance, so that the number of yeast cells in the wort is too low, or yeast coagulation is too early.

(4) Yeast is added in too small quantities, and there are no good conditions or sufficient time for it to reproduce well.

3. Fermentation temperature control

(1) If the cooling temperature is too low, the yeast will multiply slowly and start fermentation slowly, resulting in too slow sugar reduction.

(2) If the cooling temperature of the main fermentation is too fast, the temperature of the fermentation liquid will drop rapidly, and the yeast will coalesce and settle prematurely, thus affecting the rate of sugar reduction.

4. Wort pH control

If the wort pH is low, the yeast will settle easily and the number of suspended cells will be reduced; if the wort pH is high, the phytate will not be decomposed into inositol and phosphate, which will hinder the growth of yeast and reduce the fermentation performance.

5. Health pollution

Sudden change of the living environment of yeast puts the yeast in a bad environment, resulting in a decrease of yeast activity.

6. Other aspects

Brewing personnel operating factors or equipment problems factors, sometimes also cause slow down the rate of sugar.

In the above factors affecting the slow rate of yeast pre-bottling, in addition to controlling the composition of the wort and improving the fermentable properties of the wort, it is also necessary to pay attention to the following issues:

1. strict control of the number of generations of yeast used, to regularly expand the culture of yeast for production, in order to eliminate the higher generation of yeast.

2. yeast expansion and seed retention should be in line with the process conditions, low-temperature storage and maintenance is a very simple method, but poor control or preservation of too long a period of time are prone to autolysis of yeast, or make the yeast liquid acidic, odour, so that the yeast mortality rate increases.

3. to strictly check the germination rate, the high mortality rate of yeast should not be used in principle, such as must be used, it should be appropriate to increase the amount of yeast added and pay attention to the separation of the dead yeast cells, to strengthen the effect of yeast proliferation, including the control of the oxygen content of the wort, the control of the composition of the wort to be conducive to the proliferation of yeast.

4. to have the correct yeast addition method, including the appropriate amount of yeast added, the correct time to add yeast, the necessary oxygenation and so on. In order to ensure that the fermentation liquid normal warming, to have the right fermentation temperature, generally controlled at 8 ~ 9 ℃, or even 9 ~ 10 ℃ does not hurt. The yeast addition temperature should be based on the starting fermentation rate and should be adjusted at any time, taking into account the season, the beer variety, etc. If the yeast has a pre-saccharification rate, it should be adjusted at any time.

      If the yeast pre-fermentation rate is slow, there are also the following treatments:

1. After entering the main fermentation period, the rate of sugar reduction is still slow, you can leave the cooling water on for a while and let the high bubble temperature continue to rise by 1~2℃, or add strong yeast and fresh wort appropriately to maintain normal fermentation.

2. If the rate of sugar reduction is still not significantly improved with the extension of time and the increase of temperature, then this fermentation liquid can be divided into 3~4 portions, mixed with fresh wort and strong yeast respectively, for appropriate adjustment and compensation.