Saccharomyces Mycoderma. Oval or elliptical cells, often in branching chains. They form the so-called "mould" on fermented liquids, and develop on the surface without exciting fermentation. When forced to grow submerged they produce a little alcohol.
Saccharomyces Exiguus. Conical cells, appearing in the after-fermentation of beer.
Saccharomyces Pyriformis. Oval cells, converting sugary solutions containing ginger into ginger-beer.
Saccharomyces Illicis, Hansenii, et Aquifolii produce a small percentage of alcohol.
2. Acetous Fermentation.
Cause, Mycoderma aceti; medium, wine and other alcoholic liquids; result, the formation of vinegar.
If alcohol be diluted with water, and the specific ferment mixed with it and exposed to the air at 22° C., it is rapidly converted into vinegar. The change is accompanied by the absorption of oxygen, one atom of which combines with two of hydrogen to form water, and a substance remains called aldehyde, further oxidation of which produces the acetic acid. We may express it chemically thus:
| Alcohol. | Aldehyde. Water. |
| C2H6O (+ oxygen and the ferment) = C2H4O + H2O. | |
The aldehyde becomes further oxidised:
C2H4O + O = C2H4O2 (acetic acid).