Gelling basics: Gelatin
Gelling may well be one of my favourite transformational techniques. Controlling texture is always an important part of food, and gelling agents offer you the useful ability to turn liquids into solids.
Essentially, gelling happens when you dissolve an ingredient into the liquid that you want to gel, and it combines in a network of linked molecules and prevents the water from moving freely. Suddenly, what once pooled now stands tall.
Some of the gelled components in my recent dinner party included the carrot flan (shown above) and sherry gel, which were set with gelatin, and the yuzu jelly, which was set with pectin. Not to mention the reduced stock-based sauces, which were gels when cold, and the El Bulli Americano, which included a gelatin-based foam.
Gelatin, in particular, offers some great benefits over other gelling agents. It’s easy to find and easy to use. It can be re-melted and re-gelled nearly endlessly, though you may have to correct for evaporated water. Used properly, it has a good texture, though it can be rubbery if you overdo it: use as much as necessary, but as little as possible. And, because its melting point is right around body temperature, it’s got great flavour release, which means, roughly, that the gelatin doesn’t interfere with your ability to taste the gelled ingredient. (After my first meal at Atelier, I e-mailed Marc to ask what gelling agent had been used in one of the components of one of the desserts, because I had enjoyed the texture so much: turned out it was gelatin!)
That melting point is also gelatin’s greatest drawback, though: gelatin gels can’t be served hot. For that, you need a gelling agent that doesn’t melt once it’s set, or at least one that melts at a higher temperature. The easiest gelling agent for that purpose is agar, but its texture is very brittle and its flavour release isn’t as good as gelatin. Gellan is a better option, but harder to find, harder to use and more expensive.
Gelatin comes in different strengths, called “bloom strength,” so if a recipe calls for a specific weight of gelatin, you may have to convert it to the bloom strength of the gelatin you have. (Gelatin sheets are sold in different sizes so that each sheet will gel to the same degree, regardless of bloom strength.) The hydrocolloid recipe collection at Khymos has a great overview of bloom strength, and is worth reading for more information on gelatin and other gelling agents.