Beer fault  A beer fault or defect is caused by the chemical change of organic matter in beer due to the wrong production process and storage mode and leads to beer deterioration. The chemicals that cause flavour defects in beer have been produced in beer. For example, the aldehydes such as dactyl organic acids, lipids and sulfur compounds in beer influence the taste of beer. When the concentration of one or more elements exceeds the standard threshold, the flavour characteristics of beer will change and form the flavour defect of beer. In particular, fermentation byproducts, even small fluctuations of just over 1% above the threshold can have an impact on the flavor of the beer. Brewers need to be familiar with the taste of every beer that has gone bad to judge the quality of their brew. The precision of controlling materials and processes is reflected in whether the taste of beer is defective. Brewers also need to find a solution to the flavour defect by tasting different types of beer. The change of the external environment and the wrong production process are also the reasons of wine flavour defects. The lack of wine is due to the turn of the external environment caused by the chemical changes in the composition of the wine, such as the poor sanitary conditions of the winery, dirty wine, excessive use and oak cork rot, and the influence of temperature fluctuations of the wine flavour defects. Different from the flavour defect of wine, in the brewing process of beer, the concentration of inorganic chemical elements is too high due to improper production, or the malting of malt and hops in the brewing process causes microbial deterioration, which leads to the loss of beer flavour. Diacetyl is produced in yeast during fermentation and is reabsorbed in the process. Since the external ambient temperature during fermentation is lower than 26°, diacetyl is absorbed insufficiently, resulting in a threshold of less than 0.04 mg/litre in beer, which gives the beer a mouthfeel like cream cheese. This odour will persist over time. Since the decomposition of α-acetolactate produces a large amount of diacetyl, the method can avoid the beer flavour defects caused by diacetyl as follows: boil the container and clean it before the yeast fermentation. The wort should avoid contact with oxygen when the fermentation begins. The temperature is raised by 2°-3° within 2 minutes of the end of the fermentation process, which allows the yeast to reabsorb faster so that the diacetyl content reaches 0.04 mg/L in the beer and does not cross the threshold.