MILK STREET Q&A: Using yogurt in hot soup
Joanna H. from Seattle came to us with a question about one of our recipes: ""I made the chickpea and yogurt soup with parsley and dill from the May-June 2017 issue tonight and it was delicious. Thank you! However, the yogurt curdled the minute it went into the soup. Yes, it was off the heat. The taste was still great, but it didn’t look pretty. I used Fage whole-milk Greek-style yogurt and followed all your instructions. Can you assist?"" ""While we often dollop plain Greek yogurt on top of soups and stews for added tang, we avoid it when we plan to mix the yogurt into broth for a smooth, creamy texture. For that, we use regular yogurt. It’s a matter of protein. Both varieties of yogurt contain casein protein. At room temperature, the casein forms stable droplets of protein, or micelles. But heat can break those droplets apart, allowing the proteins to interact, link together and curdle. Because Greek-style yogurt is made by straining out additional liquid, the casein protein is concentrated, roughly double that of regular yogurt. That means that when exposed to heat, there are twice as many potential interactions, or twice as many opportunities for the proteins to coagulate. That reaction is what caused the yogurt to curdle. When we added Greek-style yogurt to hot soup, we got the same results. Switch to regular yogurt and the soup should be great. Too late for that? To cover up the curdles, puree a portion of the soup, then stir it back in."" This question originally appeared in the July-August 2017 issue of Milk Street Magazine.
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