That was pretty much how I'd imagined it. Then I started wondering if an argument could be made that wet feed vs dry feed would make the difference. So I thought, ok, add water to the non-buttermilk group's feed. Then I wondered about calories. But I guess you could give them as much food as they wanted.

Maybe I was overthinking it.

The term buttermilk used to refer to three different things: milk that had become soured; the milk left over from making butter with sweet cream/milk; the milk left over from making butter with sour cream/milk.

The buttermilk we buy at the store is cultured. It has added bacteria to simulate the traditional soured buttermilk.

I made some butter yesterday just so I could see the traditional buttermilk. It's pretty easy. Put some cream in a small jar with a lid and shake it until the fat separates into little butter clumps, then drain off the buttermilk.

I gave the butter to my coworker since I'm currently dairy-free, so I don't know how good it was. I sipped the buttermilk, and it just tasted like skim milk to me. That makes sense, since the alternative to buttermilk suggested by the authors of the 1925 article was dry skim milk.

Btw, I learned that you can actually overchurn butter. If you keep shaking the jar past the time that the butter and milk separate, they'll go back together and not separate again. I got some bad advice from two friends who'd helped make butter as children. They remembered having to shake the cream for a loooonnnngggg time. So they thought I hadn't worked at it long enough and told me to keep shaking. Maybe to a child it seems long, but it only took about 10 or 15 minutes.