Whey is the liquid left behind when milk separates into curds and whey during cheese making (or when you strain yogurt). Think of Little Miss Muffet. It's mostly water, but it also carries some lactose and whey protein.

There are two kinds, and they behave differently:

• Sweet whey comes from cheeses made with rennet. It has a mild, slightly sweet taste, so it's the more versatile one.
• Acid (sour) whey comes from cheeses and yogurt made with lemon or vinegar. It can be sharp, so it's best used in place of water in doughs and baked goods.

Ways to use it: heat it to make ricotta, swap it for water or milk in bread and pancakes, cook rice or oats in it, or add it to soups and smoothies. One heads-up: because it contains lactose, take extra care if you're lactose intolerant.

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