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I experimented for with xanthan gum for the first time tonight. I made a sauce which was about half roasted peppers, half savory stuff (lamb stock, beef broth, balsamic vinegar and a bit of chili powder). I added about 0.9% of xanthan gum, strained through a fine sieve and poured in an iSi whipper with 2 shots of nitrous oxide.

I served it at 50°C, the sauce was nice and so was the foam, but it took only a couple of seconds until the foam melted and it became a sauce with big gas bubbles in it. I somehow expected the foam to hold.

Anything I missed?

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Xanthan stabilizes emulsions, but not necessarily foams. But are you sure you aren't getting a case of the "runny foam" which surfaced about a week or two ago in another iSi question? –  rumtscho Dec 29 '11 at 16:38
    
@rumtscho: Are you referring to cooking.stackexchange.com/questions/19736/… ? In any case, the foam I was getting was very nice when it was getting out of the iSi whipper, but was rapidly melting. I should have taped it... –  Marc-André Lafortune Dec 29 '11 at 19:28
    
@Marc-AndréLafortune that's the question I meant, good to know that it isn't the same case. –  rumtscho Dec 30 '11 at 13:55

1 Answer 1

I suspect your first problem is using the iSi whipper. It does create foams, particularly whipped cream, but both Khymos and Texturas advise using an immersion blender or electric eggbeaters in a broad vessel (so there is room for the bubbles to pile up without interfering with your making more). Besides, xanthan is shear-thinning, meaning that it is viscous only while at rest, becoming fluid when stirred or sprayed.

The second possible problem: while xanthan is used in some air recipes and is used to stabilize whipped cream and mousses, I find it is more effective as a thickener than a foaming agent. Next time you make a foam, try using lecithin. Lecithin is mainly used as an emulsifier, but it also dramatically alters surface tension, making bubbles more stable. Very little lecithin is needed to keep foams stable, though the exact amount will depend on the proportion of oil and water. For a fat-free sauce like the one you describe, I would suggest trying 0.5% lecithin by weight (i.e., for 200g liquid, use 1g lecithin).

If you really want to use the xanthan, you can try adding methyl cellulose to it. I saw a recipe for an eggwhite-free "marshmallow foam" that called for 1.5g xanthan, 1.5g methyl cellulose, and 250ml water, plus vanilla, salt, and powdered sugar.

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On the subject of blenders - make sure that the liquid to be foamed is thoroughly blended and (especially if you're using an iSi) strained through a fine mesh sieve. The question doesn't specify, but it's possible that the foam was just too heavy. –  Aaronut Dec 30 '11 at 1:18
    
@Aaronut: right, forget to say I strained the whole thing. Answer edited. –  Marc-André Lafortune Dec 30 '11 at 6:27
    
Thanks for the answer, I'll try lecithin next time. Also, the shear thinning might explain some irregularity in the texture I was seeing. –  Marc-André Lafortune Dec 30 '11 at 6:29

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