Fluid gel

A common sauce-making technique used in contemporary recipes is the fluid gel. A fluid gel is a substance that behaves as a solid when still, but moves like a fluid when exposed to enough outside force, a property known as “shear-thinning” or “thixotropy”. The textbook example of a shear-thinning fluid is ketchup: in the bottle, even turned upside down, it stays still, but as soon as you shake it hard enough, it suddenly becomes fluid, and you end up with way too much of it all over your French fries.

There are several gelling agents that can be used to produce fluid gels – Modernist Cuisine lists gelatin, eggs, carrageenan, agar and gellan – but the one that’s both easiest to find and use, and cheapest, is agar. Alinea makes extensive use of agar fluid gels, which are termed “puddings” in the cookbook. Achatz has been using them for years, reportedly inspired by the use of vegetable purees as sauces: he wanted to give a liquid sauce the texture of a puree, which meant turning the liquid into a solid, then pureeing the solid. Agar fit the bill. It also has the benefit of being able to be served warm. (Heston Blumenthal seems to prefer gellan for the fluid gels in his Fat Duck Cookbook: the flavour release is better, but gellan is more sensitive to chemical composition, as well as being more expensive.)

The dinner party I had on the weekend involved a couple of fluid gels (and one emulsion, which I couldn’t resist putting in the photo above, both for looks and because the texture is similar): a sage pudding on the Alinea pork dish, and a yogurt fluid gel in the malt sorbet dish. They were made with slightly different techniques, showing off two ways you can make agar fluid gels. The sage pudding uses the basic technique: you steep some sage leaves in lightly sweetened and salted water, then remove them and whisk in agar, at 1% of the weight of the water, boil it for a couple of minutes, then strain and allow to set. Take the solid gel and puree it in a blender. This version of the technique can be used with any liquid that you can boil without affecting the taste. I’ve used it in the past for gels as varied as coffee, chamomile and cranberry.

The Eleven Madison Park yogurt gel uses a slightly different technique: for it, you take plain water, dissolve sugar and about 2.2% agar, boil it and let it set. Note that this “stock gel” is sweet, but otherwise unflavoured. You then take it and some Greek yogurt, blend them together until smooth, and then fold in even more yogurt, until you get the consistency you’re looking for. This approach is good for making fluid gels from liquids that you wouldn’t want to bring to a boil; Modernist Cuisine recommends it for herb purees, for example. It’s also good for making small amounts of fluid gel to order.

The biggest difference between these fluid gels and ones I’ve made in the past, though, is my Vitamix. Pureeing the agar gels was an absolute dream. It both went faster and produced a significantly better consistency than I managed with my old blender. If I wasn’t sold on the high-powered blender before, I sure am now!

Now I just have to figure out what to do with all the leftover sage and yogurt gel…

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