I always use the fat that I get from making broth for cooking, but recently, I realized that fats oxidize, not only from exposure high heat, but also from extended cooking time. I noticed that when I added some left over shrimp heads and shells along with the chicken carcass and marrow bones to make a soup stock, that it initially tasted great when I tested it a few hours into the brew, but when I left the broth to simmer the rest of the day, the broth developed an off taste. I think perhaps the Omega3s from the shrimp heads had oxidized. As I paid more attention to the quality of each batch of broth that I made, I noticed that if I leave a meat stock on the slow cooker for 24 hours, there would already a slight smell of rancidity. So, my question is, how long does it take for the different fats, chicken, pork, beef, shrimp and fish to oxidize when left to simmer, or is it better just to skim off the oil immediately as it floats to the surface?
asked byGwong (45)
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on December 15, 2012
at 02:20 PM
I really doubt you had issues with your shrimp shell stock, at least from the fats. 1 pound of shrimp has but 2 grams of fat, only 0.7 grams of PUFA. Now, you're just talking shells, there's going to be essentially zero fat in there. It's very likely something else was causing the problem.
Talking chemistry, the general rule of thumb is that every 10 degrees C you increase the temperature, you double reaction rates. Boiling at 100C means you're oxidizing fats 200 times faster than room temperature. Probably sounds scarier than it actually is.