STUDIES ON FERMENTATTON. 385 



yeast-cells, floating amorphous particles, whicli are larger and 

 more compact than those to which the turbidity of worts and 

 muddy beers is due, a circumstance which should lead us to 

 suppose that the oxygen in combination with the wort has the 

 efi'ect of modifying the nature of the amorphous deposit which is 

 produced during the fermentation of the wort. During boiling, 

 the hop yields to the wort a variety of resinous, odorous, and 

 astringent substances, which, for the most part, are held in 

 solution by the presence of sugar and dextrin. At the moment 

 when, under the influence of the yeast, which is itself more or 

 less oxidized, the sugar becomes transformed into alcohol and 

 carbonic acid, a portion of the bitter and resinous matters of 

 the hop becomes insoluble and remains in a state of suspension 

 in the liquid. It is ver}' probable that at this point it is when 

 the combined oxygen assumes its function of modifying the 

 physical structure of these insoluble particles, agglomerating 

 them, so that they become more easily deposited.* 



Moreover, oxidation tends to form a special precipitate in the 

 wort, which precipitate contributes towards the collection and 

 deposition of the very fine particles suspended in the wort, by a 



* We have remarked in our observations on No. 6 of Plate I. (p. 6) 

 tliat amongst the amorphous granular deposits of wort and beer vre often 

 find minute balls of resinous and colouring matter, perfectly spherical 

 and very dense, which if the liquids be shaken up will render them very 

 turbid, but which readily and rapidly deposit again, without remaining 

 in suspension in the least. Such then is the form in which the deposits 

 of wort in course of fermentation are precipitated, when the wort has 

 been freely exposed to oxygen. One day in the laboratory we were 

 desirous of starting a fermentation in a vessel capable of holding 12 

 hectolitres (264 gallons). But as we only had at our disposal a copper 

 capable of holding 2J hectolitres, we procured the wort from a neighbour- 

 ing brewery in two barrels of 6 hectolitres each. This wort we re-heated, 

 in portions, in oui- 2| hectolitre copper, a treatment which had the efi'ect 

 of oxidizing the wort more than it would have been in the brewery. In 

 this case the beer fell remarkably bright, and the cells of yeast were 

 accompanied by the deposit of minute agglomerations sketched in Plato I, 

 No. 6. We have repeated this experiment on a smaller scale and ha's e 

 obtained the same result. 



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