144 MORPHOLOGY AND LIFE-HISTORY OF YEASTS. 



gelatin. It may be remarked that the Mycoderma are very 

 susceptible to this treatment ; and it has been proved that, under 

 the conditions prevailing in the pasteurisation of beer, a tem- 

 perature of 60° to 65° 0. is fatal to six different species, including 

 Mycoderma rubriwi and M. Immuli ; as also to Sacch. Past. III. 

 and several species of beer yeast (Lasche (V.)). In the case 

 of several species of mucinous yeasts examined by Richard 

 Meissner (II.), the limit was found to range between 51° and 

 61° 0. according to the species. 



Since it is easier to render the yeasts innocuous than the 

 bacteria, a slighter warming will suffice when there is reason to 

 believe that the latter are entirely absent from, or harmless in, 

 the wine under treatment, and when, consequently, the task is 

 confined to eliminating the yeasts alone, in order to prevent 

 them afterwards setting up secondary fermentation and turbidity. 

 Carl Schulze (I.) has shown that, under these circumstances 

 and in presence of about 10 per cent, of alcohol, the yeasts are 

 killed by exposing the bottled wine to a temperature of 45° C. 

 for two hours. The samples tested in this manner did not 

 exhibit any alteration of flavour, though a precipitation of 

 coagulum occurred. 



The preparation of so-called unfermented and non-alcoholic 

 grape and fruit wines, which in reality are nothing more than 

 stabilised grape- or fruit-must — and which, thanks to the 

 temperance movement, are more and more coming into favour 

 — has also benefited by the observations just recorded. H. 

 Mueller-Thurgau (XII.) in particular has occupied himself 

 with this question, and has drawn up practical instructions for 

 pasteurising these beverages, by exposure to a temperature of 

 60° 0, for half-an-hour to an hour. Here also it is necessary 

 to filter off the resulting deposit, and pasteurise again. Fruit 

 juices, e.g. the cherry juice so highly appreciated in North 

 America, can also be rendered stable by similar treatment. 



The reader will now be in a position to understand and 

 thoroughly appreciate the operation of warming the curd in 

 cheese-making (as mentioned in § 182), and the influence of the 

 temperature then maintained on the subsequent progress of 

 ripening. 



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