Its a Red Dwarf joke in series 2 This blokes drinking tea and the ships computer tells him that they run out of fresh and dehydrated milk yonks ago. He then ask what kind of milk they're using now and the computer tells him Dogs milk and that it lasts longer any other type of milk, no bugger would drink it. It full of goodness, full of vitamins full of marabone jelly. and it has the added advantage of when it goes off it taste exactly the same as when its fresh.