Cold foams from a siphon

Although there are many culinary preparations that fall into the category of foam, when you say the word “foam” today, especially in the context of avant-garde cooking, what often comes to mind is a piece of equipment: the whipped cream siphon.

The idea of using a siphon to make foams other than whipped cream is attributed to, and claimed by, Ferran Adrià and his team at El Bulli. Back in 1994, they used gelatin to make a white bean foam in a siphon and served it with sea urchins, giving birth to the culinary foam as we know it today. Since then, several other techniques for making foams in a siphon have been developed; Adrià classifies them in several ways, including by texture (thick, mousse-like foams; fluid, meringue-like foams; and thin, liquid foams) and by foaming agent (gelatin; fat, such as the butterfat in whipping cream; egg whites; and starch). Certainly these categories aren’t exhaustive, but they are a useful framework for developing a new foam.

Foams made in a siphon can be served either cold or warm, though warm foams can’t be based on gelatin or fat. The simplest type of foam, if you’re just getting started with a siphon, is flavoured whipped cream. Rest assured that this doesn’t restrict you to only sweet foams; Rick Tramonto offers a recipe for a decidedly savoury goat cheese foam in his book Amuse-Bouche that’s based on whipping cream.

Gelatin-based foams are also quite straightforward, and offer the benefit of remarkable intensity of flavour, since the base isn’t diluted with cream. Gelatin also offers substantially better flavour release than butterfat. Sheet gelatin is preferable to powdered, so that you don’t have to take into account the water used to bloom the gelatin when formulating your recipe. One drawback to using gelatin is that it can be difficult to determine how much gelatin to use; use too much, and you won’t be able to dispense the foam, as I experienced when first formulating the McIntosh apple foam shown here.

How to make a McIntosh apple foam

  • 2-3 McIntosh apples, enough to make 200 grams of puree
  • 100g water
  • 1 sheet gelatin

Quarter and core the apples, and place them in a saucepan with a thin film of water. Cook over medium heat until completely softened, about 15 minutes, then pass through a food mill equipped with the finest disk. Puree the applesauce with an immersion blender, then pass through a fine strainer. (You want to make sure there are no large particles that could clog up your siphon.) Weigh out 200g of apple puree, add the water, and stir to combine. Bloom the gelatin sheet in cold water for 5 minutes, squeeze out the excess water, and place in a small saucepan over medium heat with a quarter of the diluted apple puree. Warm to dissolve the gelatin, then add the remaining puree. Pass through a strainer (really – you want no lumps) into a 0.5-litre whipped cream siphon, seal the siphon, charge with one nitrous oxide cartridge and shake. Chill for a couple of hours (or overnight if using an insulated Thermo Whip), then dispense as desired, following the manufacturer’s instructions.

You could serve this foam as a dish all on its own, dusted with a little cinnamon, or as a garnish on a larger dish. I served it on a butternut squash soup, which I had seasoned with a good amount sherry vinegar. The foam offered a nice contrast, in both sweetness and temperature, to the soup. Note, however, that when using gelatin-based foams with hot foods, you need to serve the dish immediately, as the heat will melt the gelatin and cause the foam to collapse in fairly short order.

You can find more recipes for siphon-based foams on the iSi North America website and in the hydrocolloid recipe collection at Khymos.org, and a complete chapter on foams written by Ferran Adrià in The Cook’s Book.

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