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I recently simmered a pot of chicken feet (including skin) for the first time and made an astonishingly gelatinous gelatin. It's clearly suffused with chicken fat, but I have no idea how much -- I don't think I could guess the fat % by weight or the fat:protein ratio to within a factor of 10.

I tried melting some in a tall, narrow container and letting the fat settle on top, but that was unsuccessful because 1) the gelatin fraction solidified at room temperature, and 2) some of the fat appears to be emulsified and won't separate out on its own. So, consider this a food chemistry thought experiment: Given a sample of gelatin with fat in it, how would you estimate the fat content?


Responses to some likely questions:

1) If I wanted a homogeneous, clean-looking and -tasting product I definitely should have removed the skin. This was more of a nose-to-tail-eating experiment.

2) I know a little chicken fat won't kill me. But I'm doing nutritional tracking to investigate some health issues, so a rough estimate would be useful.

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molecularrecipes.com/techniques/… –  TFD May 22 '13 at 20:11
    
@TFD Thanks, that's fascinating. But it looks like that would remove the water, leaving a mix of gelatin and fat. I'd want a method to remove just the fat or, failing that, just the gelatin. –  octern May 22 '13 at 20:24
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2 Answers

From experience with gelatinous stock from pig bits, I've found that gelatine can seem fatty, when really it's not - and gelatine is good for you in ways that fat is not.

I think your tall, narrow container idea is a good one, but first get it up to liquid temperature, and then keep it at that temperature for as long as it takes. You'll want to avoid convention currents, so take it off any direct heat. It might be enough to wrap it in a towel, or maybe you'll need to leave it in an airing cupboard or even a low oven.

Given long enough, even the emulsified component should separate out - although I can't guess whether that would be hours, days or weeks!

This does mean leaving the stock at a bacteriologically unsafe temperature for a long period - so the stock you test in this way should not be eaten. Do it on a small sample.

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Thanks for the suggestion! And I definitely understand that the analytic sample is a sacrifice in the name of science (: –  octern May 22 '13 at 16:39
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You could just use information from the USDA nutritional guide as represented here.*

*Source: Nutrient data for this listing was provided by USDA SR-21.

It's about a 1:1 fat to protein by mass, approx 3:2 fat:protein by nutrition (caloric).

In general, I don't think the extent of fat suspended in an emulsification is limited by anything. Watch Heston beat a virtually impossible amount of oil into a mayonnaise. Because of that, you can't impose any limitations on how much fat could be in there.

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I saw that USDA entry but I'm not clear on whether that's the gelatin, or the meat / skin on the feet themselves. –  octern May 22 '13 at 22:47
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