Condensed milk was once identified with armed forces as the canned product with high stability and long life is a versatile product for use in many food preparations for the soldiers. Decline of canning industry started with the advent of tetra pack technology which can ensure a storage life of 6 months to fluid milk. Concentration of any product to bring down water content and consequently the water activity is one of the oldest food technologies man had known to make them immune to bacterial spoilage. Milk is also preserved same way by evaporation and as an added insurance incorporation of sugar makes it doubly safe. Use of condensed milk has been on the decline as many consumers do not prefer the mildly caramelized odor and taste resulting from casein -lactose inter action. Lately this "ancient" product is reappearing as a convenient food ingredient useful to make many milk based products.
"Sweetened condensed milk came on the United States market in 1856, the brainchild of Gail Borden, a chronic culinary inventor. (He had already patented a prototype of a complete nutrition bar, which he called a "meat biscuit.") Mr. Borden began experimenting with sterilized milk after a series of "swill milk" scandals that revealed the true contents of much of the milk then for sale in American cities: chalk powder, molasses and vermin. His process — a combination of vacuum pressure, heat and added sugar — produced a dairy product that is nearly indestructible, with a shelf life of years. Mr. Borden made his fortune supplying condensed milk to the Union Army in the Civil War. It was airlifted into Berlin in the 1940s, and more recently has opened up Asia as a major market for American milk".
Advances made in dairy processing machinery like vacuum evaporators have made it easier to make evaporated and sweetened condensed milk products with high quality and with minimum caramelized odor. Of course spray dried milk powder offers more convenience as it does not need costly metal cans to pack and as it is 100% milk solids there is considerable flexibility in recipe development. Probably condensed milk manufacturers may still come up with products with varying sugar content to suit different needs. Many of the Indian sweet meat products based on Khoa can be made with practically no compromise on end product quality using sweetened condensed milk.