It's rather a combination of yeast and several kind of bacterias, i.e. Bacterium xylinum, that live together in symbiosis.
Structure of the Kombucha cultureKombucha is a substance that looks like gelatine in the form of a pancake.
A healthy Kombucha culture is nearly white, very light brownish and tough like leather.
It resembles at a sole of a shoe or a cartilage.
Sometimes it get brown striae that can be washed away with cold water.
Functioning of the Kombucha cultureThe teamwork between the yeast and the bacterias is like follows:
The yeast produces alcohol out of the sugar.
The bacterias need this alcohol as food and build glucuronic acid, glucaric acid, lactic acid, acetic acid and several vitamins.
Because the liquid is sour, only the right kinds of bacterias can survive in it.
The bacterias also produce the gelatinous mass, that is the physical basis of the Kombucha culture.