386 MILK 



there are some micro-organisms that seem to be capable of pro- 

 ducing peculiar bitter substances. Conn described a Micrococcus 

 lactis amari and Harrison found in bitter milk a torula which was 

 named Torula amara. Members of the coli-aerogenes group may 

 also produce protein decomposition products that impart to milk 

 a bitter taste which is usually accompanied by an odor remind- 

 ing one of stable air. These abnormal tastes develop when lactic 

 acid bacteria are absent or at least are so scarce that the acid 

 produced is not sufficient to inhibit the growth of other micro- 

 organisms. 



Sweet Curdling of Milk. — Milk sometimes curdles shortly 

 after milking before a sufficient amount of acid is present to 

 precipitate the casein. This is caused by bacteria forming a 

 rennet enzym, and occurs most frequently in cool wet summers or 

 in winter. When milk curdles without acid formation the curd 

 may be smooth or broken up (cheesy curd). The formation of a 

 curd may be due to the hay bacillus group, in which case the curd 

 is smooth, or to the acid-rennet micrococci, which produce a 

 cheesy curd. Butter is difficult to make from sweet curdled milk. 



Soapy Milk. — A soapy taste in milk appears occasionally, and 

 such milk when shaken foams similarly to a soap solution. Bacil- 

 lus saponaceus is usually the cause of this abnormal condition, 

 but the substance produced is unknown. Weigmann reports 

 another organism that is capable of producing a soapy milk, 

 Bacterium sapolacticum. This is a small non-Kquefying bacillus 

 producing a slightly fluorescent pigment. Both types occur on 

 the bedding and food of cows, and are thus transmitted to milk. 



Abnormal tastes and odors, pleasant or otherwise, caused by 

 micro-organisms which should be mentioned are: 



1. Fruit-like odor, especially strawberry odor, produced by 

 Bacillus coli. 



2. The butter flavor produced by Conn's 41. 



3. Marshall and Farrand's Bacterium fulvum, which causes an 

 unpleasant taste and odor. 



4. Lohnis' Bacterimn kirchneri, which produces a rancid odor. 

 It is sometimes difl&cult to dispose of dairy troubles that are 



caused by unusual numbers of disturbing micro-organisms. The 

 first step is to locate the origin by sampling the milk from the dif- 

 ferent producers, and thus to determine the source. It is then 

 further necessary to examine the milk from each cow in the herd, 

 so as to find the animal or animals involved. The offending 

 animals must be removed from the herd until the milk is normal. 

 The stables and utensils must be disinfected, and at the collecting 

 station the cans, coolers, botthng machines, etc., must be treated 

 likewise. Pressure steam, if applied long enough to thoroughly 



