Friday, February 25, 2011

Stock Clarification Techniques

I like to try out new techniques in the kitchen every once in a while to see how they might be useful in my repertoire. Cooking is a continual process of learning for me; if I’m not learning, why am I in the kitchen? Among the new techniques that I have tried is a method for clarifying stocks into consommés. I conducted a small series of experiments over the last year to compare the new technique to the standard technique.

Because my grounding is solidly classical, I have heretofore made my consommés using a protein fining technique, adding raw egg whites or raw chicken breast to cold stock and gently heating it. As the raw protein coagulates (cooks), it traps the impurities from the stock and with reasonable care, a clear consommé emerges after filtering the “raft” of solid protein from the liquid.

Some years ago, I learned of a technique called ice filtration (or gelatin clarification) via the famous British chef Heston Blumenthal. I doubt that he invented the technique, but he is certainly responsible for bringing it to my attention and that of chefs all over the world. The technique involves letting a stock gel (either from naturally occurring gelatin or by adding more gelatin), then freezing the gel, and then letting the gel melt very slowly such that the clear liquid separates from the gelatin matrix which holds the impurities in suspension. There is no doubt that this technique is high on cool factor; it is really quite amazing to see it in action.

Both techniques achieve the desired result of a clear liquid, but there are some significant procedural differences and clearly perceptible differences in the resulting consommé.

First the technical differences. The ice filtration technique takes almost no effort on the part of the cook, a clear win for the novel technique. But the process of chilling the stock, freezing it, and letting it thaw at refrigerator temperatures takes seemingly forever, a minimum of 48 hours for a reasonable amount of consommé. And getting the frozen stock to thaw in a reasonable amount of time involves freezing it in thin sheets; this takes a lot of both refrigerator and freezer space, space that many restaurants may not have. That’s two wins for the standard technique to one for the new technique.

Now for the qualitative factors. The ice filtration technique appears to clarify the stock slightly better than the standard method based on my observation in the kitchen. Done correctly, ice filtration gives crystal clear consommé every time; sometimes it is necessary to clarify a stock a second time using the standard technique. That’s two wins apiece, a draw so far.

My experiments concluded by tasting consommés made from the same stock using the two techniques, side-by-side and blind. The ice filtration consommé has a water-like body: all the gelatin is gone from the final product. The standard consommé has a weight to it, a silkiness that the gelatin imparts, not unlike the body that glycerin gives a wine made from ripe grapes. And I find that the ice filtration consommé tastes weaker than the standard consommé. It may be that the gelatin increases my perception of flavor; in any case, I clearly prefer the standard consommé over the ice filtration consommé every time during blind tasting. On my score card, that’s four wins for the old method to two for the new. Your mileage may vary.


  1. Speaking of stock techniques, I read an interesting tidbit in a WSJ article about "Modernist Cuisine" that you might enjoy:

    PROBLEM #5: You want homemade chicken stock, but you don't have eight hours to kill.

    SOLUTION: Chop small to chop time.

    Pulse the ingredients (typically, carrot, onion and celery) in a food processor until very finely diced; remove vegetables, add boneless chicken pieces and puree. Chop chicken wings into tiny pieces. Brown all the chicken, then add vegetables and cover with water. Simmer for an hour. The stock will attain the same flavor it would have taken 8 hours with large chunks.

    WHAT'S GOING ON: "Fick's first law of diffusivity" is at work. This principal indicates that flavor molecules have a shorter distance to travel if the pieces of food are smaller, and thus will be extracted more quickly.

    How do you feel about pressure cooking stocks?

    Do you use pressure cookers often in your restaurant kitchen?

  2. I have no opinion on pressure cooker stock versus open pot stocks. I've heard arguments for both. We don't do a lot of stocks because we don't do a lot of stock-based sauces. We don't use pressure cookers here at the restaurant. They're super expensive. I have one on my wishlist for when I get rich, but until then, it's open pot for us.

  3. Thanks so much for posting this. I've been trying to decide how to clarify some fumet I made and couldn't decide between the techniques. Based on this post, I think I've decided that the gelatin technique would be perfect for the fish fumet (it tastes a little intense to me as is, anyway) and the raft technique preferable with a chicken or beef stock.

    I'm just a home cook, so now I've just got to pray that I can pull off the execution.

  4. Have you tried stiring leaf gelatin into the clarified stock after ice filtering? It would be an extra step but would get the mouthfeel on a parity. I have heard all else being equal that classic stock loses more flavour, although I haven't done side by side comparisons.

  5. I haven't. But I have to ask, why remove the gelatin in the first place only to add it back? It is also my perception that ice filtration strips more flavor than protein fining. The point is moot now that I am retired. I certainly don't have refrigeration space for ice filtration, but it was a fun exercise and a great learning experience. I urge everyone to try it at least once.