A Study of the Organisms Causing Thickening of Sweetened Condensed Milk

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Abstract
Sweetened condensed milk, as found in the market, usually flows freely when removed from the can. The contents have a color closely resembling that of cream, and possess a pleasing odor and taste. Occasionally, however, one finds a can with the con- tents so thick that they will not flow without vigorous stirring, or, perhaps, are even solid. Two different kinds of thickening that may cause this condi- tion have been observed. One of these, commonly called heat or age thickening, apparently causes a change only in the viscosity of the milk, the taste and odor remaining normal. The other kind of thickening, which is considered in this paper, produces different conditions. In the early stages, the milk may show a normal body having clots of thickened milk throughout. Some- times the milk may be so thick that it will barely flow. In later stages it may be solid, so that it is possible to invert the can without the loss of its contents. As the degree of thickening increases, acidity and a characteristic fruity odor develops, as well as a disagreeable taste. When vigorously stirred, the milk thins slightly, but it returns to its original thickness after standing. When a portion of the milk is diluted with water and heated, a separation of the curd takes place. By this test it can be distinguished from heat or age thickened milk. This kind of thickening commonly referred to as bacterial thickening has been found to occur most commonly in late spring or summer or in shipments to tropical countries.

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