Traube (1858), the active cause of fermentation is due to the action of different enzymes contained in yeast and not to the yeast cell itself.
That such enzymes are formed in the protoplasm is evident from the behaviour of hyphae, which have been observed to pierce cell-membranes, the chitinous coats of insects, artificial collodion films and layers of wax, &c. That a fungus can secrete more than one enzyme, according to the materials its hyphae have to attack, has been shown by the extraction of diastase, inulase, trehalase, invertase, maltase, raffinase, malizitase, emulsin, trypsin and lipase from Aspergillus by Bourquelot, and similar events occur in other fungi.
Oxydases and Enzymes: Green, The Soluble Ferments and Fermentation (Cambridge, 1899).
We cannot as yet speak definitely with regard to the part played by enzymes in these toxic processes.
The preference exhibited by yeast cells for sugar molecules is shared by mould fungi and soluble enzymes in their fermentative actions.