Take beer brewing, for example. Beer fermentation requires the action of yeast. Yeast generally has two types of alienation, one is aerobic and the other is anaerobic type. When oxygen is sufficient, yeast is aerobic type, oxygen participates in yeast organic synthesis, organic matter accumulation is more, yeast multiplies quickly. When the yeast multiplies to a certain number, the oxygen is cut off. At this time, yeast breathes anaerobic and produces organic matter and alcohol, which is what we need. If oxygen is not introduced first, the number of yeasts is insufficient, and the brewing speed is slow and impure.