February 26, 2008

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Gelatin Filtration

I gave the technique of gelatin filtration (also called "ice filtration") a try for the first time a couple months back, and I'm finally posting about it. No, it did not take two months to finish filtering, though it felt like it. I just haven't gotten around to posting about it.

Normally when you make stock, you don't bother clarifying it unless you have some use for it that requires clarity (at home, anyway). But when that is the case, as for a consommé, there are all sorts of techniques for clarifying, ranging from progressively finer filters (eventually using, for instance, a coffee filter) to cooling the stock, adding egg white, then gently re-heating it, which creates a "raft" on the top of the stock with most of the impurities. Gelatin filtration is much more successful than any other method I've heard of, and is, in some sense, easier. On the other hand, it also takes a lot longer.

Here's how it works:

Leftover goop

After you make stock, it normally contains natural gelatin. If it does not (as from a shrimp stock or a vegetable stock), add it. Then freeze the resulting gelatinized stock. As it freezes, the water in the stock forms ice crystals, while the gelatin does not. The impurities in the stock (including all of the fat) get trapped in the gelatin. Then once frozen, the stock is transferred to the refrigerator to drip slowly through a cheesecloth into a new receptacle. Over a period of days (two? three?), the water crystals gradually melt and drip through the gelatin mesh, while the gelatin mesh, which has trapped all the impurities, stays all gloopy on top of the cheesecloth. When it's all done, you've got perfectly clarified, fat-free stock, that is nevertheless fully flavored. I've read that if you do this process multiple times, you can eventually achieve a perfectly clear broth that nevertheless has all its flavor. For more info, read this article.

So I decided to give it a shot. Why? Because I wanted to strike out into new ground? Because I needed a perfectly clear broth for some amazing dish? Because I had three days to kill? No. I'm sad to say it's just because I had some turkey stock cooking after a big meal, and one of my roommates decided to stir it vigorously while I wasn't around. "Mmmmm, this soup looks great." Would cloudy stock have been okay for whatever I was going to use it for? Probably so. But then I would've missed the opportunity to have half of the refrigerator's main shelf taken up for several days.

And though I was thrust into the ranks of gelatin filterers unexpectedly, the results were stunning. Perfectly clarified, but extremely flavorful turkey broth, with a pleasant, amber color. I had all my roommates try it, and all of them were surprised by the flavor intensity of this wimpy-looking liquid. Did I end up making some fabulous, shocking dish with it? No, I ended up making risotto and gravy to go with game hens. Did I need clear broth for that? No, but the risotto and gravy were awesome.

In the picture at the top, I added a cherry tomato to the bottom of the bowl to give you an idea just how clear the broth is. In person, it's much more striking than in pictures, but it still looks pretty cool. And I'd be lying if I said that I didn't drink at least a bowl full while heating it for other purposes. Yummy turkey consommé.

The main criticism of this technique is that the gelatin in a stock or consommé gives it body and mouthfeel, and in this process, you lose all of that. And it's true. In the end, it's really just extremely flavorful water. No unctuousness. But for many applications, clarity is more important. In others, you may not even want that unctuous mouthfeel. And another advantage to this technique: if your gelatin-filtered broth cools down, it doesn't turn into turkey jell-o--unless you want it to. You can always re-add gelatin. My main criticism of this technique remains the long waiting time and gobs of refrigerator space that it takes. For normal applications, I'm gonna stick to my preferred filtration method: fine-mesh strainer lined with a paper towel. And yes, I'm serious about that.

Posted by Barzelay at February 26, 2008 2:21 PM | Comments (4) | Science, Technology

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