The alcoholic ferments concerned in the production of beer will be found represented in several of the engravings in this work. Other ferments we may term “diseased”; these include all those that may occur spontaneously—that is, whose germs have not been directly and intentionally introduced—amongst the actual alcoholic ferments.
The expression, “diseased ferments,” is justified by the circumstance that the propagation of these ferments is always accompanied by the production of substances which are acid, putrid, viscous, bitter, or otherwise unpalatable, a consideration of commercial rather than scientific importance. From a physiological point of view, all these ferments are of equal interest and importance. The botanist, as a man of science, in contemplating nature, must give equal attention to all plants, whether useful or noxious, since they are all governed by the same natural laws, among which no order of merit could be established. The exigencies of industry and health require, however, wide distinctions.
[Illustration: Plate 1. Principal Disease-ferments met with in Wort and Beer.]
The first engraving (Plate I.) represents the different diseased ferments, together with some cells of alcoholic yeast, to show the relative size of these organisms.
No. 1 of the engraving represents the ferments of _turned_ beer, as it is called. These are filaments, simple or articulated into chains of different size, and having a diameter of about the thousandth part of a millimetre (about 1/25000 inch). Under a very high power they are seen to be composed of many series of shorter filaments, immovable in their articulations, which are scarcely visible.
In No. 2 are given the lactic ferments of wort and beer. These are small, fine and contracted in their middle. They are generally detached, but sometimes occur in chains of two or three. Their diameter is a little greater than that of No. 1.
In No. 3 are given the ferments of putrid wort and beer. These are mobile filaments whose movements are more or less rapid, according to the temperature. Their diameter varies, but is for the most part greater than that of the filaments of Nos. 1 and 2. They generally appear at the commencement of fermentation, when it is slow, and are almost invariably the result of very defective working.