Question

Почему при нагревании молоко пенится ,а вода нет ?:)

Answer 1

Молоко - многокомпонентная система - эмульсия жиров в воде, с примесями белков. Белок сильно повышает поверхностное натяжение жидкости. Это означает, что пузырькам воздуха сложнее покинуть поверхность жидкости. Если поверхностное натяжение достаточно велико, то пузрьки воздуха, например, образующиеся при кипячении или взбивании, "залипают" на поверхности. В результате образуется пена.

 

В чистой воде никаких посторонних примесей нет, вот она и не пенится - поверхностное натяжение недостаточное для пенообразования.

 

Answer 2

Why does milk foam when heated, but water does not?

When milk is heated, it tends to foam due to the presence of proteins and fats. The proteins in milk, such as casein, are sensitive to heat and can denature, or unfold, when exposed to high temperatures. This denaturation causes the proteins to unfold and form a network that traps air bubbles, leading to the formation of foam.

Additionally, milk contains fats, which can also contribute to foaming. Fats are hydrophobic, meaning they repel water. When milk is heated, the fats can melt and become more fluid, allowing them to mix with air and water vapor, further contributing to the formation of foam.

On the other hand, water does not foam when heated because it lacks the proteins and fats present in milk. Water is a simple compound composed of hydrogen and oxygen, and it does not have the same molecular structure as milk. Therefore, it does not have the ability to form a foam-like structure when heated.

In summary, the presence of proteins and fats in milk, along with their sensitivity to heat, contribute to the foaming effect when milk is heated. Water, lacking these components, does not exhibit the same foaming behavior.

I hope this explanation helps! Let me know if you have any further questions.