Milk

Milk was a nutritious liquid produced and secreted by the females of certain species. While milk was typically white, the one produced by bantha cows was blue, the one produced by Skarasens and thala-siren sea sows was green, and the one produced by po'acksters was pink. 
Some intelligent species would farm non-sentient creatures to extract their milk and use it as food. When left standing for a while, milk would turn sour. However, to prevent spoilage, it could be stored in cool places, just like meat. Milk was the basis of various preparations that included ice cream, yogurt, and butter. Tooka were known to enjoy milk.
== Milk-Producing Species ==
Whether the female of a species exuded milk from its nipples or from simple ducts to nurture its young was one of the defining traits of mammals. Similar nourishing substances were produced by non-mammalian species. Malmooth could drink their own internal milk, while the green milk produced by Skarasens was fed on by the Zygons. 
The only known cure for spectrox toxaemia was the milk from a queen bat, a species native to Androzani Minor. The cure was discovered by Professor Jackij. 
The seemingly male Sontarans could be genespliced to produce milk. Strax was very proud that he could produce "magnificent quantities" of lactic fluid and offered to nurse Melody Pond. 
== Milk as a beverage ==
Milk was also used by other species as a drink. The humans of Earth harvested and drank the milk of cows. Milk was sold in cartons or glass bottles, and delivered by milkmen. In some locations, such as the planet Sto, milk was sold in a milk market. 
Milk was often used in tea and coffee to add taste. It was sometimes drunk warm as a sleep aid.
Like humans, cats often drank milk. One one occasion, this made the cats of the United Kingdom vulnerable to alien attack. When a fungus from space found its way into Britain's milk supply, cats all over the country turned on their owners in a series of savage attacks. 
== Milk as an ingredient ==
Milk was also the base ingredient for many foods, known as dairy foods.