What chemical reaction happens when milk becomes foam? How does milk become foam?

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Although you don't need a degree in chemistry, it's a more complicated technique to understand the chemical effects of milk on coffee. However, if you want to make a perfect and beautiful milk foam flower, then you must seriously learn about milk. Milk varies with the cow's diet, health, food and place of residence, which can affect its composition and taste.

Assuming that all cows grow in the same place and eat the same food, the following three factors have a direct impact on milk: Lactose, milk fat and protein content.

Lactose sweetens milk. Lactose is a disaccharide molecule, composed of galactose and glucose and co-existing in milk. Lactose does not break down in water and does not taste sweet when it cools, but when heated, it becomes soluble, releases sugars and increases sweetness.

Pour whole milk and skim milk into two cups respectively and you will find that skim milk has a light taste and texture, compared with water, and has no special feeling after drinking it. However, whole milk is thicker and feels weightier. Why? This is because the content of milk fat is different. Whole milk contains 4% or more of milk fat. What we often call Cream is a thin layer of cream formed on the surface of milk, which contains more cream and tastes better than the milk itself.

Through machine extraction, manufacturers can adjust the milk fat content to 2% (equivalent to 50% concentrated),?% (equivalent to almost all milk fat concentrated), and degreasing (removing all milk fat, leaving only water, protein and sugars). In theory, whole milk can give coffee a strong taste, but some people still like skim milk because they think that the milk fat in whole milk is harmful to health.

Then let's talk about milking. Protein is the third factor that baristas pay most attention to after lactose and milk fat. When you heat the milk, the protein changes from the sol state to the gel state, forming a film that surrounds the air molecules and forms a floating substance, commonly known as milk foam. Milk fat content, protein, and temperature all affect the formation of milk bubbles.

If the fat content increases, the stability of foaming will be reduced. So it's much easier to use skim milk to make a lot of thick foam than whole milk. However, when the milk fat content reaches 5% or more, the stability of milk bubbles will be relatively improved. So you will find that the foam made in the state of 10% milk fat is quite dense and stable. This is why edible liquid cream, which contains 18% milk fat, and whip cream, which contains 35% milk fat, are so stable and produce so much.