Milk
Milk was a creamy white emulsion produced from the mammary glands of several mammalian species, including the Earth cow and the Klingon targ. Cetaceans on Earth produced milk to nurse their calves. (; ) 

Containing rather significant amounts of nutrients such as proteins, saturated fats, calcium, and most notably, Vitamin D, it was often consumed on Earth as a beverage. When warmed it would act as a sedative. Two percent milk was one of several beverages offered in the drink dispensers in the mess halls of  starships. ()

Milk could also be processed into dairy products such as cheese, yogurt, and ice cream, as well as incorporated into various kinds of dishes.  Persons unable to tolerate drinking milk would consume milk alternative instead. ()

Widin Dairy Farm delivered milk via a horse-drawn cart to the inhabitants of New York City in 1930. ()

Lieutenant Kevin Riley drank milk from a tinted glass while on duty in the engineering section of the  before it was poisoned with tetra-lubisol by Lenore Karidian in 2266. ()

In 2268, when Ensign Pavel Chekov was served vodka at the bar on Deep Space Station K-7, Lieutenant Commander Montgomery Scott made fun of his choice of drink by asking when he was going to get off of that milk diet. ()

In 2365, a hologram of  offered milk to go along with the tea of his hostage, Doctor Katherine Pulaski, which she accepted. ()

That same year, Jean-Luc Picard illustrated the cultural importance of the horse to ancient Human cultures by describing how a fine warhorse would sleep in a Bedouin's tent, carry him into battle, and provide milk for his children. ()

Geordi La Forge compared the spaceborne species dubbed  feeding on the energy of the USS Enterprise-D to an infant being fed with milk. In order to dispose of the creature which was rapidly draining the ship's power, he realized that he had to "sour the milk". ()

The farmers in the Galar system raised spider cows as livestock and as a source of milk. If a spider cow was stunned by a phaser, this would spoil the animal's milk. ()

In 2381, Ensign D'Vana Tendi served Lieutenant Commander Steve Stevens a glass of milk after his annual physical revealed that he had very weak bones. ()

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de:Milch
Beverages
Biochemical compounds