A Text-book of the Science of Brewing by Edward Ralph Moritz George Harris Morris

Author:Edward Ralph Moritz , George Harris Morris
Language: eng
Format: epub, pdf
Publisher: E. & F.N. Spon
Published: 1891-03-25T05:00:00+00:00

310 A Text-Book of the Science of Brewing.

at present in use for obtaining the spores—namely, by the cultivation of yeast upon plaster blocks partially immersed in water and kept in a damp atmosphere. As we shall see later, Hansen has utilised the formation of spores as a means of distinguishing between different Fig- 6. varieties of yeast.

^ iL b Reess' classification of

the Saccharomycetes is as follows:—

The Saccharomyces are simple Ascomycetes without. ^^^^ js^^^ a true mycelium. They are

^^J fX^'i unicellular plants, multiply-

^ . .... . ing themselves by the forma-

Sacch, cerevtsut, showing vanoi^ stages ^ ^

of budding. (After De Bary.) tion of buds which sooner or

later separate themselves from the mother-cell (Fig. 6). A portion of the cells produced by budding directly develop to spore-forming asci. Number of spores in ascus, usually 1-4. The germinating spores multiply themselves directly by budding.

a. Species thoroughly examined :—

Sacch. cerevisicB^ ellipsoidens^ conglomeratus^ exigitus, and Pastarianus.

b. Species incompletely known :—

Sacch, Mycoderma, and 5". apiailatus,

I. Socc/l cerevisicB, Meyen (Fig. 6). The cells mostly round or oval, 8-9 /x % long, isolated or united in small colonies. Spore-forming cells (asci) isolated, 11-14 /x long; spores mostly three or four together in each mother-cell, 4-5 /x in diameter. The alcoholic ferment of beer.

There are two varieties of this species, the so-called " top "

* /i is the most common abbreviation for the micro-millimetre, which is the name given to the unit of microscopical measurement, and which is equal to one thousandth of a millimetre.

or " high/* and ** bottom " or " low " yeast The bottom-yeast sets up a fermentation in beer-wort at temperatures from 40** to 50® F. ; the fermentation continues for eight to ten days, and the temperature during this period rises 2*5® to 4*5® F. During the period of the fermentation only a very slight scum is formed on the surface of the fermenting liquid, and this scum contains only a very small proportion of yeast-cells. Both the old as well as the newly-formed yeast-cells settle on tlie bottom on the fermenting vessel as a dense sediment, sharply separated from the liquid. Bottom-yeast consists of round or slightly oval cells with a diameter of 8-9/i, they are said to be slightly smaller and more oval than the cells of the top-yeast

Top-yeast requires a higher temperature for its action than bottom-yeast—namely, 54® to Jj^ F.; and the fermentation is usually complete in two to three days. The newly-formed cells rise to the surface of the liquid, and there form a large foam-like head. The ferment is distinguished from bottom-yeast in that its budding cells form more ramified clusters than the budding cells of the latter, which usually occur singly or in pairs. The cells also bud more freely, and the clusters of cells are carried to the surface by the carbonic acid evolved.

The earlier observers, Caignard de Latour, Turpin, and Mitscherlich, considered top-yeast to be morphologically different from bottom-ycast, and this was generally accepted until Pasteur in his earlier memoirs, concluded that the two

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.