122 DAIRY BACTERIOLOGY 



exposed to strong sunlight for only one hour, its surface becomes 

 bleached and perfectly uneatable. The taste thus produced bears 

 the closest resemblance to that of bad tallow, and is generally 

 described as " talloivy." The rancid taste proper is only produced 

 by the microorganisms, and is due to the lower members of the 

 fatty acid series, i.e., the volatile fatty acids, as well as certain 

 esters which have a fruity odour, such as ethyl and amyl acetate. 

 The glycerine, which is usually completely transformed by the 

 microorganisms, is, the starting substance in the formation of the s 

 esters as well as of the alcohols which may be formed. As most 

 fat hydrolysing organisms require air for their development, the 

 exclusion of air is the most important precaution necessary to 

 protect the butter from the changes under discussion. For this 

 reason, butter intended for use in warm climates is packed in 

 hermetically sealed tins. Heat, like sunlight, promotes the 

 oxidation of the fat. According to Ritsert 1 , carbonic acid, even in 

 darkness, will impart a tallowy taste to butter ; this point is not 

 without bearing on the ripening of cheese, as considerable quantities 

 of carbonic acid are often produced in cheese. 



The most important fat hydrolysing microorganisms are Bac- 

 terium fluorescens liquefaciens, Bacterium prodigiosum, Oidium 

 lactis, Penicillium glaucum and Cladosporium butyri. As they do 

 not form spores, they are all easily destroyed on heating ; of 

 the two bacteria, B. fluorescens liquefaciens is, as mentioned 

 above, very widely distributed in water, for which reason there is 

 a danger in letting butter come into contact with water or ice. 

 In many cases the advantages gained by pasteurisation are 

 nullified when we introduce bacteria with the washing water, 

 which have a worse effect on the keeping qualities of the butter 

 than those which were destroyed in pasteurising. It should be 

 made a principle to pasteurise (in a regenerative apparatus) all 

 the water used for rinsing the cream cans, ripening tanks and 

 churns, and for washing the butter. Moulds may come from the 

 starter (or from the milk if the cream has not been pasteurised), 

 from the air or from the packing material. By treating the casks 

 and parchment paper for twenty -four hours or longer with con- 

 centrated brine, nutrient substances are extracted and the mould 

 spores are considerably weakened. It is better to treat the 

 inside of the casks with melted paraffin wax immediately before 

 use ; they will then be sterilised and rendered airtight. If this 

 is done, parchment paper may be dispensed with, and the wood 

 will not soak up brine and increase the tare at the expense of the 

 nett weight 2 . Although Oidium lactis and Penicillium glaucum 



1 Inaugural dissertation, Berne, 1890. 



2 Rogers, U.S. Dept. of Agric., Bureau of Anim. Ind., 1906, Bull. No. 89. 



