🧪 Water

Water is the main part of milk. Whole cow's milk is about 87–88% water: roughly 87.8 g per 100 g. Everything else is “dry matter”: fat, proteins, lactose (milk sugar), minerals and vitamins. They are dissolved in the water or float in it as tiny droplets and particles.

Milk needs water so that it is liquid and easy for the young animal to drink. Lactose and many minerals are dissolved in it. The protein casein and the fat droplets stay suspended in the water, which is why milk is cloudy and white. The amount of water in milk differs between animals. According to the FAO, yak milk is about 83% water and donkey milk about 91%. The less water, the thicker and more filling the milk.

Removing water is the basis of many dairy products. Boil off part of the water and you get condensed milk. Remove almost all of it and you get milk powder. Milk powder keeps for a long time because germs need water to grow. Cheese and cottage cheese are also made when a lot of water leaves the milk along with the whey. But adding water to milk is not allowed: that is fraud.