Alcoholic fermentation / by Arthur Harden.

  • Arthur Harden
Date:
1932
Catalogue details

Licence: In copyright

Credit: Alcoholic fermentation / by Arthur Harden. Source: Wellcome Collection.

    34/258 page 24
    only about 20 per cent, of the cells are left unaltered by one grinding and pressing, and only 4 per cent, after a repetition of the process, at least 57 per cent, of the cells being actually ruptured by the double process, and the remainder to some extent altered. It seems probable from these figures that a certain amount of the juice may be derived from the unbroken cells, and Will expressly states that many un- broken cells have lost their vacuoles. If the yeast be submitted to a process of regeneration, which con- sists in exposure to a well-aerated solution of sugar and mineral salts until fermentation is complete, the juice subsequently obtained is more active than that yielded by the original yeast [Albert, 1899, 1]. A slight modification of Buchner’s process was introduced by Harden and Young, the mass being ground in a mixing mill instead of by hand. The ground mass is then well mixed with a further quantity of kieselguhr until a nearly dry powder is formed, and the mass packed between two layers of chain cloth in steel filter plates and pressed out in a hydraulic press at about 2 tons to the square inch (300 kilos, per sq. cm.). The press and plates are shown in section in Fig. 2. It has also been found convenient to remove yeast cells and kieselguhr from the freshly pressed juice by centrifugalisation instead of by filtration through paper, and to wash the yeast before grinding by means of a filter-press. Working with English top yeasts Harden and Young have found the yield of juice extremely variable, the general rule being that the amount of juice obtainable from freshly skimmed yeast is smaller than that yielded by the same yeast after standing fora day or two after being skimmed. The yield for 1000 grams of pressed brewer’s yeast varies from 150 to 375 c.c., and is on the average about 250 c.c. As a rule a juice which gives a more vigorous reaction with phosphate (p. 43) is obtained if the ground mass be kept for two hours at air temperature before it is pressed out [Harden and Henley, 1927, 1]. Very fresh yeast occasionally presents the peculiar phenomenon that scarcely any juice can be expressed from the ground mass, although the latter does not differ in appearance or consistency from a mass which gives a good yield. Extraction of Zymase from Unground Yeast. 1. Maceration of Dried Yeast. A valuable addition to the methods of obtaining an active solution of zymase was made in 1911 by Lebedev [1911, 2 ; 1912, 2 ; see also
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