Learn the simple reason why a layer of cream or film can form on top of your milk in the fridge. Discover what's happening to the milk fat.
1 Answer
The film that forms on milk in cold storage is primarily caused by the coagulation of milk proteins, particularly casein, and the oxidation of fats at the surface. This process is accelerated by exposure to air and temperature fluctuations.
Detailed Explanation:
When milk is refrigerated, several factors contribute to the formation of a surface film. Firstly, milk contains proteins, mainly casein, which can denature and coagulate over time, especially at colder temperatures. This coagulation leads to the formation of a thin layer on the surface. Secondly, the fats present in milk, particularly unsaturated fats, can undergo oxidation when exposed to air. This oxidation process results in the formation of a slightly hardened or thickened layer. The combination of protein coagulation and fat oxidation creates the visible film. Furthermore, temperature fluctuations within the refrigerator can exacerbate this process, as repeated warming and cooling cycles promote both protein denaturation and fat oxidation. The film is generally harmless, but it can affect the milk's texture and taste.
Pro Tip:
To minimize film formation, store milk in an airtight container and avoid placing it in the refrigerator door, where temperature fluctuations are more significant.