The next time you find your milk has gone sour, don't throw away the carton in disgust. Instead, calmly return it to the fridge and make a mental note: You have a great excuse to bake this weekend, because while you may not want to drink a glass of spoiled milk, it makes a great substitute for a hard-to-find ingredient.

The extra acidity in "aged" milk can actually add extra flavor to baked goods, like cakes or muffins. "It's a substitute for buttermilk," says chef Dan Barber. "You can [use it] in pancake or biscuit batter. And you can't taste the sour!" However, you may be wondering if this DIY buttermilk substitute will make you sick.

As it turns out, the pathogens that cause food-borne illnesses are different from the ones that develop in aging milk, but you still need to make sure the milk has simply soured and not degraded beyond that. You should definitely toss milk if mold has formed inside, which means unwanted bacteria could be present.