BUTTER 609 



developed in the ripening process of cream. The substance oxi- 

 dized may be the result of a hydrolysis of .one of the constituents 

 of butter by the acid." Fishy flavor is more common in hot 

 weather than in cold, and occurs when cream overripens or when 

 it is overworked. But high-acid cream does not always produce 

 a fishy butter. The flavor is not apparent in fresh butter, but 

 develops during storage. Rogers found no bacteria or molds 

 responsible for the fishy flavor. By making butter from pasteur- 

 ized cream the occurrence of the fishy flavor is prevented. 



For bacteriologic examinations of butter a sample of 200 to 

 300 grams is drawn with a sterile butter trier. The sample is 

 melted at a low temperature (35 C.) in a sterile glass jar. When 

 melted a portion is poured into an Erlenmeyer flask and kept at 

 about 35 C. in a water-bath. All dilution flasks and pipets 

 must be kept at the same temperature to prevent hardening of 

 the butter. From the liquid butter, dilutions can be prepared and 

 plates made in the usual manner. One gram of butter equals 

 about 1.15 c.c. 



CHEMICAL ANALYSIS OF BUTTER 



Samples are taken with butter samplers. The whole sample 

 is melted in a closed vessel at low temperature. The melted but- 

 ter is shaken until homogeneous and until sufficiently solid to 

 prevent separation of water and fat. 



Determination of Moisture. Evaporate 1.5 to 2.5 grams to 

 dryness on a water-bath and desiccate over calcium chlorid. 



Determination of Fat. Dissolve with absolute ether or petro- 

 leum ether the dry butter obtained in the determination of moist- 

 ure. Transfer to a Gooch crucible with the aid of a wash bottle 

 filled with the solvent, and wash until free from fat. Dry the 

 crucible and contents on a water-bath and calculate the fat. 



Determination of Casein, Ash, and Chlorin. Cover the cru- 

 cible containing the residue from the fat determination and heat 

 gently at first, raising the temperature to just below redness. 

 Remove the cover and heat until white. The loss in weight is 

 casein; the residue, mineral matter. To determine the chlorin, 

 dissolve the mineral matter in water slightly acidulated with 

 nitric acid. To this solution add a known volume of normal one- 

 tenth silver nitrate solution until an excess is present. Stir 

 well, filter, and wash the silver chlorid precipitate thoroughly. 

 To the filtrate and washings add 5 c.c. ferric indicator (a satur- 

 ated solution of iron alum) and a few cubic centimeters of nitric 

 acid. Titrate the excess of silver with one-tenth normal ammo- 

 nium or potassium thiocyanate solution until a permanent light 

 brown color appears. Calculate the amount of silver nitrate solu- 



39 



