A skin had formed on the top of the milk.

奶上结了一层奶皮。

《牛津词典》

On top of that, most of the 3D food printers now are restricted to dry ingredients, because meat and milk products may easily go bad.

最重要的是，现在大多数的3D食品打印机都受到限制，只能打印干燥的食材，因为肉类和奶制品很容易变质。

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Joseph's top priority became getting his hands on enough grass-fed milk to keep customers satisfied, since his own 64-cow herd wasn't going to suffice.

约瑟夫的首要任务是弄到足够的草饲牛奶来满足顾客的需求，因为他自己64头牛的牧群还不足以满足。

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This process is what stops the cream from separating again and floating to the top while milk sits on a grocery store shelf or in your fridge.

FORBES: Why Milk Isn't As "Natural" As You Think

So far, milk production has increased to about 18 pounds each from his top animals this month, up from less than a pound of milk in March.

WSJ: It's Easy to Be Cowed When Trying to Milk a Water Buffalo

At the SGF conference, I learned that the chief commodity to get people through the door, particularly on the top-up for the big shop, is milk.

BBC: Shelves in a shop