Question

a home brewer sets up a container with grain, water, and yeast. she opens the container twice per day to check the progress and gently stir the mixture. assuming she had all of the essential ingredients in the proper amounts, why cant she make beer? the grain must have been very poor quality and lacked enough sugar and starch to support fermentation. opening the container so frequently supplies the yeast with oxygen for cellular respiration; they never switch to fermentation. stirring just makes it worse! opening the container so frequently introduces oxygen, which kills the yeast before they can ferment the grain. stirring just makes it worse! the container should never have been closed. the buildup of co₂ is detrimental to fermentation. i dont know yet

Explanation:

Beer brewing relies on yeast fermentation. Yeast can perform both cellular respiration (with oxygen) and fermentation (without oxygen). When there is oxygen (like when the container is opened frequently), yeast will do cellular respiration and not switch to fermentation which is needed for beer - making. Stirring can further mix in more oxygen.

Answer:

Opening the container so frequently supplies the yeast with oxygen for cellular respiration; they never switch to fermentation. Stirring just makes it worse!