"Can I Remove Heat by Removing Fat?"
"Since capsaicin is fat-soluble, by skimming the fat from my chili, am I effectively removing all the heat from it?"
—Submitted by Serious Eats user, "The MKT"
It's no secret that capsaicin, the hydrophobic* compound that gives chili peppers their heat is most concentrated in the fleshy white membranes that surround the seeds of a chili**, so by removing those sections before cooking, you can significantly tame the heat that'll end up in your finished dish. But what about in a dish that's already finished? Since capsaicin is fat-soluble, would taking the fat out of a finished dish remove all the heat as well?
*Hydrophobic things are things that hate water but love fat, sort of like my Boston terrier Yuba.
**At least, it should be no secret, and if it is, then you need to find some more interesting things to keep from other people.
No, Removing Fat Will Not Reducing Spiciness
The short answer is no, it won't. Why not?
How Capsaicin Works
First, let's take a look at how capsaicin works. Capsaicin is an organic compound very similar in shape to vanillin (the molecule that gives vanilla its characteristic aroma). Its key difference is a long hydrocarbon tail, which not only makes the molecule very heavy (and thus odorless and extremely un-volatile—that is, it won't fly off into the air very easily), but also helps it bind to lipoprotein receptors on cell walls. Once bound to a cell, it triggers a reaction that causes the cell to undergo a reaction identical to the one caused by exposure to heat.***
***For a more detailed look at capsaicin and the other related vanilloids, take a look at this article from General Chemistry Online.
That burning sensation you feel on your tongue? It's actually not a flavor sensed by your taste buds in the same manner as, say, sweetness or saltiness. It's an actual physical reaction that tricks your cells into telling your brain that they have been burned. Because that hydrocarbon tail has the ability to fit through cell membranes, the burning sensation can be quite long-lived, and because capsaicin has such an affinity for fat and dislike of water, drinking cold water to wash it away won't help.
Can We Get Rid Of It?
So if the capsaicin is all bound in the fatty phase of a chili or a spicy Sichuan dish, why can't we just remove that phase and get it over with?
There are a couple of reasons.
First off, it's nearly impossible to remove all fat from a dish. Sure, there's the big red oil slick that forms on top as you simmer a dish down, and while this may form a large part of the dish's fat content, there's still plenty of fat in the rest, either in the form of small droplets emulsified into the liquid, or within the meat and vegetables themselves. Our sensitivity to capsaicin is so great that even ten parts per million will trigger a reaction. Ain't no way you're going to get all of that capsaicin out of there.
Secondly, while it's true that large capsaicin molecules are not dissolvable in cold water, they are slightly soluble in hot water, and easily soluble in alcohol****. If I'm not mistaken, chili is usually served hot. And if you're like me, it's probably got some form of booze in it as well, whether it's a shot of bourbon or a pint of beer. So even after you've got the fat off the top, you're still going to have capsaicin dissolved directly into the liquid.
****If you've ever had a spicy alcoholic drink, you'd know this. It's also why beer or a shot of vodka will work better than plain water at cooling your mouth after a chili binge. Milk, with its lipophilic casein proteins, is better still.
Even if you refrigerate or freeze that chili, the capsaicin may break out of solution into microscopic solid crystals, but there's no way to get them out of a thick chili. They'll stay there until you reheat the stew and they can dissolve once again.
So if you take the fat off of your chili, you may be cutting down on heat a bit, but bear in mind that you'll also be cutting down on all the other wonderful fat-soluble flavors that have made their way into it, not to mention the flavor of the fat itself, which when stirred back into the chili, can be quite delicious.
Moral of the story: Let that fat be. If you want to cut down on chili heat, use fewer chilies, or cut out their white pith and seeds before adding them.
This question was originally published as part of the column, "Ask The Food Lab."