Culinary airs
Foams are common in the kitchen. Egg whites and meringues, a head of beer, whipped cream, cappuccino etc. What’s modernist about foams is pushing the limits a bit. For example, can it be lighter and airier, and can liquids that don’t foam of their own accord be foamed?
One way to achieve this is to add a surfactant. Think of these molecules as a short rod, one end of which is hydrophilic (water-loving) while the other end is hydrophobic (water-avoiding and gas-preferring).
When the surfactant is dissolved in a liquid and the mixture beaten to introduce air, the surfactants arrange themselves on the surface of the air bubbles such that the gas-loving ends are in the bubbles, and the water-loving ends are pointing outwards into the liquid. Thus the surfactant coats the surface of the bubbles and stabilises them.
An example of a surfactant that is fairly readly available is soy lecithin. You’ll probably find it in health food shops, although it may be granular and perhaps not de-oiled, so an online culinary supplier might be necessary. The point is that it is nothing unusual as an ingredient, just the application.
Not much is needed - just 0.3 to 0.4% by weight of lecithin can foam tap water. It is aerated with a stick blender, or even an aquarium bubbler (that oxygenate fish tanks). The amount will differ according to the liquid though.
Citrus air
125ml lemon juice, 125ml lime juice, 250ml water (all at room temperature), 2g lecithin (0.4% by weight). The mix should be cold. The water dilution is necessary to reduce the intensity of the acidity, and because acidity retards foaming. Here it’s been draped over chicken. Light and fresh in flavour.
Salt air
This is foamed salted water — soft and unexpected. There are no other ingredients. To 500g cold water, add 70g salt and 1.8g lecithin. Don’t be too fussed if the scales are only to 1g accuracy, 2g is fine. Don’t be tempted to add too much though, it works against foaming when concentrations rise too much. Use wherever a garnish of salt is appropriate. Ferran Adria makes a margarita omitting the salted glass rim and adding a dollop of salt air instead.
Try a bit of salt air on an oyster in its half-shell. Or, citrus air.
