A curdling tale: Home-cultured sour cream

Continuing with my curiosity about fermented milk products, but lacking the time for a full-fledged cheese project, I decided to take on something a little more set-it-and-forget-it: sour cream.

In the idyllic past, cows would be milked and the milk would be left to stand, allowing the cream to separate and rise to the top. Since this was all taking place at ambient temperature, mesophilic (“moderate-loving”; i.e., that prefer room temperature) lactic acid bacteria would also thrive. Leave this cream to stand for long enough, and those bacteria turn it noticeably sour. At the same time, the acid thickens the texture by rearranging the protein molecules.

Nowadays, the processes are much more controlled. Milk is pasteurized, cream is separated using centrifuges, and sour cream is made using pure strains of bacteria. Since I already had some of those bacteria on hand, in the form of starter culture, all I had to do was slightly warm some cream, add the culture, and let it sit for 12 hours at room temperature. I used whipping cream, which was probably overkill, but it worked anyway, producing a tart, curdled cream.

For no other reason than that I had it on hand, I added some of my newly soured cream as a garnish on an acorn-squash-and-walnut risotto. I usually enrich risotto with a little cheese or butter or both, so cream seemed to be in keeping with that habit (although I know many people would cry heresy at the addition of any form of cream). Plus, the tanginess of the cream seemed like a good way to offset the sweetness of the squash, which I had cooked sous vide with butter and brown sugar. Turns out I was right.

Of course, that used only a small amount of the sour cream, and I have quite a bit left. So what’s your favourite use for sour cream?

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