76 MILK ANALYSIS 



According to Konig, good kefyr will not contain more than 

 I per cent, of lactic acid. 



Analytic Methods. — Fixed solids and ash are determined 

 by evaporations of a weighed amount in a platinum basin as 

 described on page 1 1 . Acidity is determined by filtration with 

 -^ alkali, using phenolphthalein or methyl-orange as an indica- 

 tor. The amount of acidity is expressed in terms of lactic acid. 

 The Kjeldahl-Gunning method will give the total nitrogen. 

 For further examination of the nitrogenous bodies, the methods 

 given on pages 71 and 73 may be applied. Total reducing 

 sugars may be estimated as given on page 27. If sucrose 

 and common yeast have been added, the fermented material 

 will be likely to contain invert-sugar, with unchanged lactose 

 and sucrose, and the method of examination of sweetened con- 

 densed milk may be applicable. Fat can, probably in all cases, 

 be determined with sufficient accuracy by the L-B. process. 

 If it be desired to make polarimetric readings, the liquid should 

 be clarified with acid mercuric nitrate solution (page 30), as 

 some partly hydrolyzed proteids which have rotatory power 

 may not be precipitated by other reagents. The determination 

 of alcohol accurately is difficult, as the quantity is usually small. 

 The cautious distillation of a considerable volume of the ma- 

 terial previously neutralized with a little sodium hydroxid will 

 yield a distillate in which alcohol may be determined by specific 

 gravity. 



Preservatives are not likely to be used, since they would 

 interfere with the fermentation, but attempts may be made to 

 secure better keeping by adding some preservative after the 

 fermentation has occurred. In some cases, therefore, tests 

 for boric acid, formaldehyde, and salicylic acid should be made, 

 as these will be most likely to be used. 



