Culinary foams bless both savory and sweet preparations -- custards, puddings and whipped-cream toppings, for example -- are common foams you use in everyday cooking. The difference within foam preparations is density. Nonconventional foams, such as those composed of butter, derive their lightness from natural ingredients applied with nonconventional methods. Butter-based foams are attained with vigorous whisking and timely serving -- but they only last a few minutes. Stable foams -- those that maintain stability for up to 1 hour -- require natural emulsifiers and stabilizers and a whipping siphon.
A la Minute
Add 1 tablespoon of butter for every serving of the preparation you wish to add foam to to a heavy-bottomed saucepan. Set it on the stove, set the heat to medium-low and whisk until foam forms.
Skim the foam from the surface of the simmering butter and ladle it over the preparation using a spoon. You have 2 to 3 minutes before the air within the foam dissipates.
Reserve the clarified butter for another use. You can cool the butter and reheat it to the simmering point, but the more you reheat, the weaker the foam will be.
30- to 60-Minute Foam
Heat 1 pound of butter to 100 degrees Fahrenheit in a 6-inch-tall, heavy-bottomed saucepan until it starts to separate -- then cut the heat. If you are using an electric stove, remove the saucepan from the burner.
If your kitchen has an ambient temperature of 100 F or above, you can simply let it melt in the saucepan to the foaming point within 1 hour.
Sprinkle 2 grams (.070 ounce) of soy lecithin or 1 gram (.035 ounce) of xanthan gum over the butter. Using the immersion blender, whip the butter until it froths to the height of the saucepan.
Pour the foamed butter into the fully charged siphon using a funnel. Hold the siphon with the nozzle about 1 to 1 1/2 inches above an empty plate. Squeeze the siphon trigger in short bursts until you get a feel for the amount of foam it releases with the pressure of the trigger pull. When you are comfortable with applying the butter foam, hold the nozzle about 1 to 1 1/2 inches above the preparation.
Squeeze the siphon trigger and add the butter foam to taste. You can apply the foam to the preparation about 30 minutes before you serve it, if you keep the preparation at room temperature. Butter foam holds its structure for up to an hour, but for best presentation, serve as soon as possible.