The principle of traditional fermentation to make pickles.

Yeast for fruit wine needs oxygen at first. When the yeast grows to a certain amount, it begins to isolate oxygen, allowing it to carry out anaerobic respiration to decompose glucose to form alcohol.

Sufu is made of Mucor. protein in tofu is turned into small molecule protein by the enzyme of Mucor, which is easy to be absorbed by people.

Pickled vegetables are fermented by lactic acid bacteria which produce lactic acid. Lactic acid bacteria fermentation needs to isolate oxygen.

Generally speaking, it uses anaerobic respiration of microorganisms.