On many farms where butter is made for home use it is desirable to put away some of the surplus summer butter to use during the late fall and winter when production is sometimes not sufficient for the family needs. Many farmers, after using special care in making summer butter that they think will keep well, have put it away only to find a few months later that it has become strong and rancid. This experience is not confined to farm butter. The city dealer in creamery butter has had the same experience even when he stored it in a good cold-storage warehouse. Experimental work in the United States Department of Agriculture a number of years ago showed that the sourness of the cream greatly influenced the keeping quality of the butter and that butter of the best keeping quality was made from perfectly sweet Pasteurized cream.