什麼是奶

雌性哺乳動物在產後一段時期從乳腺分泌的汁液，可用來餵養幼雛。馴養動物的奶也是人類重要的食物來源。西方國家主要從母牛身上取得奶，在別的地區，奶的主要來源包括綿羊、山羊、水牛和駱駝。奶基本上是水中脂肪和蛋白質的乳狀物，也含有已溶解的糖（碳水化合物）、礦物質（包括鈣和磷）以及維生素（維他命）（特別是維生素B複合體）。商業上出售的牛奶還添加了維生素A和D。許多國家都要求對牛奶進行巴氏殺菌法，以防止天然滋生或是人為造成的細菌。進一步冷凍可防止腐敗（變酸或凝結）。全脂奶（3.5%的脂肪含量）可經過乳脂分離器加工產出乳脂和含1～2%的脂肪的低脂奶或含0.5%脂肪的脫脂奶。商業上出售的奶通常已經透過高壓被均質化，奶油分佈均勻。奶可以被濃縮或脫水以便儲存和運輸。其他的奶製品還包括奶油、乳酪和酸奶。

milk

Liquid secreted by the mammary glands of female mammals to nourish their young. The milk of domesticated animals is also an important food source for humans. Most milk consumed in Western countries is from the cow; sources important elsewhere include the sheep, goat, water buffalo, and camel. Milk is essentially an emulsion of fat and protein in water, along with dissolved sugar, minerals (including calcium and phosphorus), and vitamins (particularly vitamin B complex); commercial cow's milk is commonly enriched with vitamins A and D. Many countries require pasteurization to protect against naturally occurring and artificially introduced microorganisms. Cooling further prevents spoilage (souring and curdling). Fat from whole milk (about 3.5% fat content) can be removed in a separator to produce cream and leave low-fat milk (1-2% fat) or skim milk (0.5% fat). Commercially sold milk is usually homogenized, forced under high pressure through small openings to distribute the fat evenly. It may also be condensed or dehydrated for preservation and ease of transport. Other dairy products include butter, cheese, and yogurt.