UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION' 
 BERKELEY 4, CALIFORNIA 
 
 PREVENTION OF RANCIDITY IN FARM BUTTER 
 
 E. L. JACK 1 and N. P. TARASSUK 2 
 
 Rancidity is the most common form of spoilage 
 of farm butter. It is characterized by objection- 
 able flavor and odor, generally called "rancid" 
 or "strong," sometimes "bitter" or "wintry." It 
 is caused by chemical breakdown of the fat; the 
 degree of breakdown influences somewhat the 
 term used by persons tasting the butter. Rancid 
 butter is not unwholesome, but in advanced 
 stages is exceedingly unpalatable. In farm but- 
 ter the defect is generally of one of two types — 
 spontaneous rancidity, which develops within a 
 very few days after the butter is made; and mold 
 rancidity, which, if it occurs, generally does 
 not appear until the butter is 2 or 3 weeks old. 
 
 SPONTANEOUS RANCIDITY 
 
 Spontaneous rancidity is reported mainly from 
 farms where the milk of only one or two cows is 
 used for buttermaking. It is most common during 
 the winter, when cows are fed principally on dry 
 feed. The milk of cows late in their lactation 
 period (that is, cows which have been milking a 
 long time) often develops spontaneous rancidity. 
 When the cream, under these conditions, is 
 churned, the buttermilk frequently tastes bitter; 
 and the butter becomes "strong" in flavor after 
 2 or 3 days. Indeed, such cream churns only 
 with difficulty and sometimes not at all. 
 
 Spontaneous rancidity of butter is caused by 
 the enzyme lipase, secreted in the milk. When 
 persons encounter this difficulty the natural 
 questions to ask are whether the milk and butter 
 are safe to use and whether the cow is healthy. 
 The answer to both of these questions is "yes": 
 the milk is wholesome; and the cow is healthy, 
 at least so far as relates to rancidity. No 
 concern need be given to the question of health. 
 The problem is rather one of palatability and of 
 preventing the trouble. Several different ways 
 of overcoming or reducing this type of rancidity 
 are discussed below. One of these may be suf- 
 ficient, or a combination may be necessary. 
 
 Assistant Professor of Dairy Industry and 
 Assistant Dairy Technologist in the Experiment 
 Station, 
 s 
 Instructor in Dairy Industry and Assistant 
 Dairy Chemist in the Experiment Station. 
 
 Washing the Butter 
 
 The tendency to rancidity and other types of 
 spoilage may be greatly reduced by washing the 
 butter several times with clean, cold water. 
 This should always be done. 
 
 Mixing the Milk 
 
 As Tarassuk and Henderson 3 have shown, ran- 
 cidity does not develop where the milk contain- 
 ing the lipase is mixed with milk that does not 
 contain it. Mixing should be in the proportion 
 of one part of the former to four parts or more 
 of the latter, and should be done within an hour 
 after milking and before cooling, or at least 
 immediately after cooling. The effect of mixing 
 explains why spontaneous rancidity is more com- 
 mon when the milk from only one or two cows is 
 used. If possible, the milk from cows that have 
 been milking a long time — 8 or 9 months — should 
 be mixed with milk from cows recently freshened. 
 
 Effect of Feed 
 
 Spontaneous rancidity in butter is most fre- 
 quently reported in the winter, when only dry 
 feed is available. Often a cow is kept confined 
 and given dry hay when, with a little effort, 
 green pasture could be used. Although green 
 feed will not always overcome the difficulty, 
 it will do so in many cases; and always it will 
 reduce the intensity of rancid flavor. Every 
 effort should therefore be made to provide green 
 feed, either pasture or freshly cut grass. 
 
 Effect of Late Lactation 
 
 Cows that have been milking 9 months or more 
 may give slightly bitter or salty milk, the but- 
 ter from which will develop spontaneous ran- 
 cidity. When late lactation is the obvious 
 cause of the trouble, the solution is to put 
 the cow dry. When she freshens again, the but- 
 ter made from her milk will probably be all 
 right. 
 
 Tarassuk, N. P., and J. L. Henderson, 
 vention of hydrolytic rancidity in milk. 
 Journal of Dairy Science 25:801. 1942. 
 
 Pre- 
 
 UNIVERSITY OF CALIFORNIA 
 
 LIBRARY 
 
 COLLEGE OF AGRICULTURE 
 DAVIS 
 
 [1] 
 
Pasteurization 
 
 Sometimes it is impossible to apply any of the 
 remedies suggested above — namely, mixing the milk, 
 supplying green feed, or putting the cow dry. 
 Or perhaps the remedies available will not over- 
 come the difficulty. The solution then is to 
 pasteurize the milk or cream. This, if properly 
 done, prevents the development of spontaneous 
 rancidity; and it is the only sure method. Since, 
 however, pasteurization is bothersome, people 
 will usually not take the trouble with small lots 
 of milk or cream until they have tried all other 
 methods. Pasteurization is valuable also in 
 destroying other agents, such as bacteria, that 
 may exist in milk and that would cause butter to 
 spoil. Greatly superior butter can be made from 
 pasteurized milk or cream; this method is used 
 almost universally in commercial buttermaking. 
 
 Either the milk before separation, or the 
 cream, may be pasteurized. Treating the cream 
 is preferable where a small hand separator is 
 used. The cream from the night milking can be 
 held over and mixed with that from the morning 
 milking, and all pasteurized together each day. 
 Cream that is to be pasteurized should not be 
 kept longer than 18 hours after the milk is 
 drawn from the cow. If the milk must be set for 
 the cream to rise, one should pasteurize the 
 milk immediately after drawing it and before 
 cooling. 
 
 Nelson 4 describes a procedure for pasteurizing 
 small quantities of milk or cream. A large pan 
 or kettle of water is so arranged that the water 
 can circulate around and under a smaller vessel 
 containing the milk or cream. Cream should be 
 heated to 150°F and held for 30 minutes, then 
 promptly cooled. Milk may be pasteurized at 150° 
 
 Nelson, D. H. Home buttermaking. California 
 Agr. Ext. Cir. 68:1-16. 1942. 
 
 for 30 minutes and then cooled; or it may be 
 brought to 175° and cooled immediately. Cream 
 will rise more completely from milk heated to 
 175° flash than from milk heated to 150° for 30 
 minutes. 
 
 MOLD RANCIDITY 
 
 Rancidity caused by mold contamination usually 
 does not become noticeable until butter is 2 or 3 
 weeks old. As a rule, farm butter is eaten be- 
 fore that long, so that moldiness is not a prob- 
 lem. Sometimes, however, more butter is made 
 than will be used at once, and the surplus must 
 be stored till a later time. Unless precautions 
 are taken, this stored butter will mold and spoil. 
 
 Refrigeration 
 
 Commercially, butter is kept at -10° to -20°F; 
 but such refrigeration is not available on many 
 farms. Butter for home use can be stored in salt 
 brine without refrigeration. 
 
 Butter in Salt Brine 
 
 Nelson also gives directions for preparing a 
 suitable salt brine. A stone jar or wooden keg 
 may be used; it must be clean and scalded im- 
 mediately beforehand. Boil for 15 minutes enough 
 water to cover the butter, and dissolve in it 
 2-1/2 pounds of table salt per gallon of water. 
 If no scales are at hand, have the brine strong 
 enough to float a fresh egg. Wrap the butter 
 securely in parchment or "butter" paper, and 
 place it in the brine. Since butter will float 
 if left to itself, lay a plate on top of it, and 
 put a weight on the plate to keep the butter 
 submerged. Good butter may be kept in this way 
 for several months. 
 
 [2] 
 
 5m-May, '44(292)