. Laboratory work in bacteriology. Bacteriology. YEASTS. 387 Most of the saccharomyces can give rise to alcohol and are, therefore, of great industrial importance. Certain species induce the alcoholic fermentation at a temperature of 14 to 18° and are known as the top or upper yeasts, whereas other forms are active at a lower temperature, 4 to 10°, and are hence commonly designated as bottom or Imver yeasts. 0^. Fig. 55. Yeast cells with spores (Hansen). The common Saccharomyces cerevisiae is a typical upper yeast. It is used in brewing and in baking. The ordinary compressed yeast contains thi
. Laboratory work in bacteriology. Bacteriology. YEASTS. 387 Most of the saccharomyces can give rise to alcohol and are, therefore, of great industrial importance. Certain species induce the alcoholic fermentation at a temperature of 14 to 18° and are known as the top or upper yeasts, whereas other forms are active at a lower temperature, 4 to 10°, and are hence commonly designated as bottom or Imver yeasts. 0^. Fig. 55. Yeast cells with spores (Hansen). The common Saccharomyces cerevisiae is a typical upper yeast. It is used in brewing and in baking. The ordinary compressed yeast contains this organism mixed with more or less starch. It forms large, round or oval ; Not infrequently, in brewing, this organism is contaminated with other yeasts or even with bacteria, and the products elaborated by these foreign organisms may greatly alter the composition and general characteristics of the beer. As a result of the studies of Pasteur and of Hansen, on these so-called diseases of beer, it has become customary in large establishments to employ only pure cultures of yeasts. The most common cause of the spontaneous fermenta- tion of gtape and other fruit juice is the Saccharomyces ellipsoideus. Secondary fermentations or "diseases" may occur in wine as in beer. A group of species which fre- quently show sausage-like cells are known as the S. Pastorianus. ' The torula group contains the so-called wild yeasts. These rarely give rise to thread-like forms, and never pro- duce spores. As a rule, they cannot produce more than. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Novy, Frederick George, 1864- . Ann Arbor [Mich. ] G. Wahr
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