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So I have an iSi whipped cream charger. There are a series of recipes that sound really interesting, but I don't quite understand what ingredients you need in order to make a stable foam / mousse. Some common ingredients seem to be cheese, cream, and gelatin. But I've also seen recipes with chocolate and water (melted and combined), lecithin, or even scrambled eggs with sous vide eggs, skim milk, and butter.

So what ingredients are a must for making a foam? How do they work?

I must admit, I'm more interested in the "how" than the "what". The what seems to be pretty well defined in the list or recipes, but I want to be able to create my own culinary treats and understanding the process is invaluable in making things up.

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2 Answers 2

up vote 6 down vote accepted

A foam is just a liquid with plenty of air incorporated into it. You can incorporate air into any liquid; in order to be able to create an actual foam, however, you need to be able to incorporate the air faster than it escapes.

What makes a liquid able to hold the air you're incorporating (and hence form a foam) is a foam stabilizer, also commonly called an emulsifier1. I know of no specific taxonomy of stabilizers, but the vast majority are hydrocolloids AKA gelling agents and belong to some family of protein.

  • Agar, carrageenan, alginate, xanthan, and pectin are all types of polysaccharide;
  • Lecithin is mostly a random collection of phospholipids;
  • Gelatin is denatured collagen, i.e. animal protein;
  • Whey protein is the prevalent protein in dairy products;

And so on. Really almost any emulsifier will do. Basically everything in your list either is, or contains, one of the the additives mentioned above:

  • Chocolate is almost always emulsified with soy lecithin;
  • Eggs contain high amounts of lecithin;
  • Milk and cream contain whey protein;
  • Most "supermarket cream" also has emulsifiers like carrageenan already in it.

...you get the picture, I hope. The most basic answer I can give to this is that if you want to make a foam, you need to either use something that's already an emulsion (milk, butter, chocolate, etc.) or use an emulsifier/stabilizer additive (such as gelatin, lecithin, etc.)

If you want a relatively complete list of all of the food additives that qualify, you'll want to look at the E number, and specifically E400-499 (thickeners, stabilizers, emulsifiers).


1. As commenter Erik very correctly points out, an emulsifier is not the same thing as a foam stabilizer. However, by convention, the terms seem to be used interchangeably all over the place, to the extent that I get blank looks when I refer to a "stabilizer" as opposed to "emulsifier". So, know the difference, but don't get too hung up on it.

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How much of a gelling agent do you need to add? I assume you don't want to add so much gelatin that the liquid actually sets. Is there a guideline to how much I should be using? What role does temperature play in a foam holding? –  yossarian Jan 18 '11 at 21:12
    
+1 Awesome answer as usual. One tiny nit to pick: although functionally a foam stabilizer is the same as an emulsifier, the two words don't literally mean the same thing - as you say, a foam is air (or any other gas) in a liquid, an emulsion is a liquid in another liquid (into which it cannot dissolve). It's just that the chemical processes keeping them together are the same. –  Erik P. Jan 18 '11 at 21:15
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@yossarian: Every single gelling agent has completely different properties. The hydrocolloid recipe collection has a partial list of foaming/gelling concentrations for the most common ones. In addition you may need to take certain preparation steps (i.e. heating) before they'll work their magic. It all depends on the specific additive. With gelatin, you need a 0.5-1.5% concentration (by weight), you need to bloom it first, and you need to heat it to at least 50° C to dissolve it properly. –  Aaronut Jan 18 '11 at 21:16
    
@Erik: The confusion between terms actually drives me crazy, but unfortunately, everybody out there refers to foam stabilizers as "emulsifiers"; immersion blenders even come with "emulsifying blades". I considered trying to emphasize the difference but I was worried I'd just end up creating more confusion. –  Aaronut Jan 18 '11 at 21:18

There are many, many methods to making a mousse. From simply folding melted chocolate into cream, to making a ganache and then folding that in, to making italian meringue and folding that in.......Normally, it is always something folded into a whipped cream.

My favourite way to make a supple, nice, flavourful mousse is to prepare a bombe, and fold that in.

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Thanks for the answer, but I'm specifically interested in foams being formed by a whipped cream charger like the iSi. The down vote wasn't me, but I assume that's the cause of it. –  yossarian Jan 18 '11 at 21:10
    
Fair enough, apologies that I wasn't specific. I realize that you were looking for specifics, I just wanted to put in my two cents. I guess in that case, I just need to leave a little comment on the bottom of the original post (I'm still fairly new at this). –  mrwienerdog Jan 19 '11 at 0:18

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