One has only to ferment a certain quantity of mulberry leaves, chop them up and squeeze them, and so obtain a liquid, to find in it millions of ferments and vitrios.
Fermentation now includes all changes in organic compounds brought about by ferments elaborated in the living animal or vegetable cell.
There are two distinct types of fermentation: (1) those brought about by living organisms (organized ferments), and (2) those brought about by non-living or unorganized ferments (enzymes).
The value of oak bark depends upon the amount of tannin contained in it, which varies much, depending not only on the growth of the tree but on the care bestowed on the preparation of the bark itself, as it soon ferments and spoils by exposure to wet, while too much sun-heat is injurious.
By Ewart; Reynolds Green, Introduction to Vegetable Physiology; The Soluble Ferments and Fermentation; Detmer, Practical Plant Physiology, trans.