Because condensed milk is highly concentrated full-fat milk with almost saturated white sugar, Europeans invented such high-concentration portable dairy products for long-term travel, which are not only convenient to carry, but also difficult to deteriorate. Because high-concentration desserts or pickles will make bacterial cells unable to survive because of water infiltration, condensed milk can be refrigerated after opening the lid.
Extended data:
Inferior condensed milk will have the following situations:
Lactose crystals grow or precipitate during storage. The temperature of sweet condensed milk changes too much during storage, which may increase the crystallization of lactose. Because when the temperature rises, the lactose solution changes from saturated state to unsaturated state, which makes fine crystals dissolve, and when the temperature drops, it becomes supersaturated solution, which makes the lactose crystals increase.
The formation of buttons. Due to the action of mold, white, yellow or reddish brown cheese-like clots may be produced in condensed milk, which are shaped like buttons, which makes the product have the taste of metal or cheese.
Fat separation. When the viscosity of condensed milk is too low, fat separation sometimes occurs. At rest, a part of the fat will gradually float up, forming an obvious yellowish pasty fat layer. Due to the vibration and shaking in the process of handling and loading and unloading, a part of the fat layer will be mixed again, and it will show a spotted or striped appearance after opening the can.
Baidu Encyclopedia-Condensed Milk Hygienic Standard 9. 1