Ingredient

Gelatine

Gelatine is collagen, extracted and dried. It sets liquids into a wobbling gel that melts at body temperature — which is why a jelly, a panna cotta and a mousse all feel the way they do and nothing else quite replicates it.

How it sets

Dry gelatine is coiled protein. Soaked in cold water it absorbs many times its own weight — blooming — and swells. Warmed, the coils unwind and disperse through the liquid. Cooled, they partially re-associate into a three-dimensional network that traps the liquid inside it.

That network is held by relatively weak bonds, which is the whole character of gelatine: it melts at around body temperature. A gelatine jelly dissolves in the mouth, which no other common setting agent does, and it is also why gelatine desserts must be kept cold.

The set is reversible. Warm it and it liquefies; cool it and it sets again. That is unlike starch or egg, and it is useful — a mis-set jelly can be melted and started over.

Leaves, powder and strength

Leaf

Soaked in cold water for five minutes, squeezed, and stirred into warm liquid. Easier to measure, cleaner-tasting, and the usual professional choice.

Powder

Sprinkled over cold liquid and left to bloom, then warmed to dissolve. Never tip it into hot liquid, which clumps it.

Bloom strength

Leaves are sold in grades — bronze, silver, gold, platinum — with different strengths per leaf. A recipe specifying leaves without a grade is ambiguous, and weighing is more reliable than counting.

Rough guide

Around 1.5 to 2% of the liquid weight gives a soft, spoonable set; 2.5 to 3% gives a firm, sliceable one. Start there and test.

Testing a set

Chill a spoonful on a cold saucer for a few minutes. Far better than waiting six hours to discover it is wrong.

Vegetarian alternatives

Agar sets much firmer, at a higher temperature, and does not melt in the mouth. It is a different texture, not a substitute.

What stops it setting

• Fresh pineapple, papaya, kiwi, fig, mango and ginger contain enzymes that break down protein. Gelatine is protein, so it never sets. Cooking the fruit first destroys the enzyme and solves it; tinned fruit is already heat-treated and fine.
• Boiling. Gelatine loses strength if boiled. Dissolve it in warm liquid, never a bubbling one.
• Too much acid or alcohol weakens the set. Very acidic or very boozy recipes need more gelatine.
• Not enough gelatine, or a strength grade different from the one the recipe assumed.
• Not fully dissolved. Undissolved granules do nothing and leave a gritty texture. It should be completely clear before it goes in.
• Freezing. Gelatine gels weep and collapse on thawing.

What it is used for

• Jellies and aspics, the obvious case, where the whole dish is the set.
• Panna cotta and blancmange, where a very light set holds cream just short of pourable.
• Mousses and bavarois, where a small amount stabilises whipped cream and egg foam so they hold their shape.
• Marshmallow and nougat, where gelatine holds an aerated sugar syrup.
• Glazes and mirror glazes, where it gives shine and body.
• Firming up a stock or a sauce that lacks natural body — a leaf or two gives a thin stock the lip-sticking quality a long-simmered one has.
• Clarifying, in a gelatine filtration, where a frozen and thawed gel traps solids and lets a clear liquid drip through.

Common questions