Why Is The Beer Sour

We often get messages from people asking why some of the beers they drink are sour (not sour beer), is it because the beer has gone bad? Why is the beer sour?

Firstly, we need to know that the acidity of beer comes mainly from the following.
1. dissolvable acids such as organic acids and inorganic acid salts contained in raw materials.
2. inorganic acids (e.g. phosphoric acid) or organic acids (e.g. lactic acid) that are added during the brewing process as a result of the need to adjust the pH.
3. metabolic products of yeast fermentation, including a wide range of organic acids.
4. dissolution of CO2, partially combined into weak carbonic acid.
5. contamination with miscellaneous bacteria, producing large amounts of sugar metabolites such as lactic acid and acetic acid.

From the above reasons for the formation of beer acidity can be seen, except for the contamination of miscellaneous bacteria can be avoided, other than the process of beer production is bound to occur, but can be controlled or adjusted. For example, the amount of acid added when adjusting the pH of the mash by adding acid, changes in acid composition due to adjustments in yeast fermentation conditions, the degree of CO2 saturation, etc.
In actual brewing it has been found that the cause of sour beer is generally due to contamination with stray bacteria and often occurs when the outside temperature is high and the fermentation room temperature is on the high side. If care is not taken to control the sanitary conditions of the equipment, operation and environment, there are many opportunities for contaminating stray bacteria and the rate of acid production and the increase in acidity is relatively high.

The main sources of contaminants in the brewing environment are raw materials, air and water. Yeast is also often brought in as a result of poor management, starting from wort manufacture until packaging into product beer, almost every process has the potential to contaminate with contaminants, in terms of the potential for contamination, in the following general ways.
1. raw materials (especially raw materials with high moisture content) after crushing, placed too long; using wet crushing plant, crushing time is too long.
2. mash or wort having a resting stage below 60°C.
3. wort filtration difficulties, too long filtration time, the temperature of the wort that has been filtered gradually decreases and reaches a temperature that can stain bacteria.
4. wort cooler, cold wort pipeline does not pay attention to cleaning sterilization, cold wort pipeline conveying distance is too long, pollution of miscellaneous bacteria is serious.
5. fermentation tanks, storage tanks, sake tanks are not often cleaned and sterilised, or the water used for washing is contaminated with various miscellaneous bacteria which are not clean themselves.
6. compressed air, fermentation between the air pollution of miscellaneous bacteria.
7. Pipes, valves, elbows, joints, liquid level pipes and equipment, operating tools in direct contact with materials are not clean, making wort or beer contaminated with bacteria.

After contamination with miscellaneous bacteria, as long as the growth conditions and temperature are suitable, the miscellaneous bacteria will multiply rapidly, and if the contamination is with acid-producing bacteria, the acidity of the beer will rise quickly. Although some stages of the beer making process are at high temperatures, such as wort boiling, which can kill the bacteria, the metabolites secreted by the contaminated bacteria - the acids - are not always removed. In addition, after the wort has been cooled and contaminated, it is impossible to kill the bacteria, but at most the multiplication of some bacteria is inhibited by the low temperature and the lowering of pH, but the secretion of metabolites is ongoing, so once contaminated with bacteria, the acidity is likely to increase.