Brewing requires supplies of yeast cultivated in a bacteria-free environment. If only one foreign body enters the brew during the processing, the resulting drink may resemble sour milk.
釀酒用的活酵母必須在無菌室中培養，只要有一個野酵母的孢子或乳酸菌侵入，啤酒的味道和顏色就會變得如同酸牛奶。