Creating a culinary foam is easier than it looks, and - unlike some other modernist techniques – the appropriate equipment won’t require you to break the bank.
There are two main implements that are used to make a foam. One of them you may already have in your cupboard; the handheld immersion blender. This particular tool is expert at whipping up lighter foams (froth) but less successful when it comes to preparing espuma of the Ferran Adrià variety. For denser foams, it is probably wise to invest in an espuma gun – which is designed for this very task and uses gas canisters of N2O (Nitrous Oxide).
The joy of foams is that they can be both sweet and savoury. Examples of sweet foams include James Sommerin’s cardamom espuma and Simon Haigh’s banana espuma, but there are a diverse amount of options available - so don’t limit yourself. Ferran Adrià’s forty-second sponge cake, which is made with an espuma gun and a microwave, represents a more adventurous application of the equipment.
Savoury foams – like Colin McGurran’s ham version – tend to be made from watered down purées (though viscous enough to remain stable) and used to sauce the other components on the plate. If you are preparing a warm foam, be careful not to overheat it – exceeding 60°C is generally a bad idea.
At the other end of the spectrum is frozen foam – which can be made as simply as the term suggests, though ideally you would use a blast chiller rather than a household freezer. Dehydrated foam is another intriguing prospect, and has a wonderful meringue-like texture.