lo Feb., 1911.] Pure Yeasts or " Leviires.'^ iii 



their rapid and complete separation in the shape of a curdy sediment, the 

 supernatant wine being left clear and limpid. In the ca.se of others, the 

 yeast cells do not so unite, but remain long in suspension, causing the 

 iwine to be cloudv or even milky for a lengthy period, ultimately forming a 

 slimy and troublesome deposit. 



It is, in fact, this self-curdling power of certain champagne yeasts 

 which first led to the extensive use of cultivated yeasts in practical wine- 

 making. The convenience of such easily eliminated sediment is peculiarly 

 suited to the champagne system of handling wines, since it greatly facilitates 

 the degorgement process.* The second or bottle fermentation, responsible 

 for the effervescence of sparkling wines, is now-a-days always started by 

 means of pure cultures of yeasts which possess this property in a high 

 degree. The advantages of rapid clarification apply with almost equal 

 force in the case of non-sparkling wines. Most of the cultivated yeasts 

 supplied by the trade are selected with a view to this valuable quality. 



Resistance to Certain Adverse Conditions. — Many varieties of yeasts 

 possess marked powers in certain definite directions. Some can resist 

 higher temperatures than others, without suffering injury. Some can 

 continue to transform the sugar in spite of the presence of a high pro- 

 portion of alcohol in the fermenting liquid ; in other words, they are 

 capable of carrying attenuation further. Resistance in other directions, 

 such as to high acidity, to a large proportion of tannin, &c., are possessed 

 by certain varieties, each of which may prove of great value under given 

 conditions. 



In the grape we find two clo.sely allied sugars known to science as 

 glucose and levulose, the relative proportions of which differ according 

 to conditions and degree of ripeness. In very ripe grapes, levulo.se pre- 

 ponderates. The majority of ferments transform glucose with greater 

 ease than levulo.se, the fermentation of which is usually looked upon as 

 difficult; nevertheless, certain yeasts are known which ferment levulose 

 with ease. Such should prove of value when dealing with over-ripe 

 grapes. 



Lengthy and very technical considerations cannot be fully gone into in 

 an article, such as the present one. Enough has, however, been said to 

 show the absolute necessity of selecting one's yeast, with a view to the 

 composition of the must which it will have to ferment, and the conditions 

 of temperature, &c., under which it will have to do its work, rather than 

 the somewhat sentimental rec(jmmendation that it has been selected from 

 .'lome celebrated vineyard in France or Germany. These are considerations 

 which are often allowed to exert an unreasonable amount of weight. It 

 IS true that our knowledge is as yet far from perfect on many of these 

 [K>ints. These, however, are the main considerations by which one ought 

 to be guided in the choice of yeast. It must be rememiiererl that the 

 composition of the grapes varies considerably from one year to another, 

 so that the yeast most suitable one season may not be so the next. The 

 natural or spontaneous ferment adjusts itself to circumstances, Init this is 

 not .so with the artificially adiled one. 



Production of bouquet. — Although this is tlie direction in which the 

 greatest advantages were looked for when pure yeasts were first tried, 

 it is undoubtedly the one in which the greatest disappointments have been 

 experienced. This phase of the (juestion will receive further consideration 

 in the next paragraph. 



• Di'vnrgement \» the name (jiven fo the operation hy which the sediment result inn frnni the tw^ttle 

 fermentatfon of champagne in removed prior to recorking the Bnished wine. 



