Food Science: What is Buttermilk?

In all our recent posts on buttermilk and what to do with it, we realized that there's one topic that we haven't covered.

What, exactly, is buttermilk?!

Traditionally, buttermilk is the liquid that is leftover after churning butter. It's low in fat and contains most of the protein originally in the milk. True buttermilk ferments naturally into a thick, tangy cream.

These days, buttermilk is usually made by introducing a bacteria culture to low-fat milk and then heating the mixture. We've never had naturally fermented buttermilk, but we hear that commercially-made buttermilk is thicker and tastes more tart than the traditional stuff.

Can anyone who's had "real" buttermilk confirm?

Related: Recipe: Chilled Buttermilk Soup for Hot Summer Days

(Image: Emma Christensen for the Kitchn)

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