35.4 Molecular techniques in the pastry shop

Molecular gastronomy brings new tools into the pastry kitchen.

• thickeners that work cold
• foams
• unusual gels
• powders
• liquid nitrogen
• small burst-in-the-mouth spheres

Many of the ingredients come from specialty food stores or online suppliers.

Thickening without heat

Some thickeners work with no cooking at all. Modified starch and xanthan gum are blended straight into a cold liquid, so a sauce keeps a fresh, raw taste. Xanthan, carrageenan and alginate as sauce thickeners are covered in see chapter 22: Gums and modern thickeners.

Foams and espuma

A foam is air trapped in a liquid or a solid. Mousse, soufflé, whipped cream and the froth on a cappuccino are all foams, and bread, pancakes and muffins are foams that have set. To build one, dissolve a thickener or gelling agent in a liquid or a purée, then whip it until it is as stiff as you want. Some mixtures break down if whipped too long without a stabilizer.

Espuma is Spanish for froth or foam, and in the kitchen it means a foam pushed out of a siphon (ISO) bottle charged with gas. A siphon needs no egg or other emulsifier, so the flavor stays pure, and it puts far more air into the mix than whipping does. Choose naturally light, thin flavors, since a strong one fades as air goes in. A stabilizer helps it hold its shape but is not always needed, and a filled siphon can be stored ready for service.

A well-made foam adds flavor without bulk, and it changes texture as it melts in the mouth. Gelatin and lecithin are common stabilizers for it.

Gels: firm, brittle and fluid

Setting a liquid such as a fruit purée lets you cut it into shapes. Gelatin works, and so does agar agar, made from red algae; both are described in see chapter 7: Gelatin, agar and pectin.

• A brittle gel is firm but fragile. Its network is weak, so it crumbles and melts in the mouth and releases its flavor as it breaks. Agar agar makes one, though with sugar it turns more elastic. Carrageenan, locust bean gum and low-acyl gellan gum give brittle gels as well. How much gelling agent and how much liquid you use both change the result.
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• A fluid gel sits between a sauce, a gel and a purée. It holds still like a solid but flows when stirred or shaken, and the harder and longer it is worked, the more fluid and finer it gets. It has a rich, creamy texture and can be served hot or cold, since many of its gelling agents survive high heat.
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Drying and powders

Drying a food concentrates its flavor and changes its texture; a dried apple crisp is nothing like a fresh slice. Grind it to powder and it changes again. Maltodextrin, or tapioca maltodextrin, mixed into a fat turns it into a powder. Maltodextrin dissolves in water, so a powdered olive oil or peanut butter becomes oil again on the tongue.

Liquid nitrogen

Liquid nitrogen freezes food with no freezer. It is clear and colorless at −196°C (−321°F), and it is used mostly to make ice cream and frozen foams. It is poured onto the food, freezes it, then boils off in a thick fog that can be part of the show. It is never eaten. Give it time to boil away completely and let the dish warm enough that it cannot hurt the diner.

Spherification

Spherification turns a liquid into small spheres with a thin skin and a liquid center that bursts in the mouth. They can be large or tiny, like "caviar", and soft or firm. There are two ways to do it.

• Direct. Dissolve sodium alginate in the flavored liquid, mixing well because it turns sticky, and let it stand until the bubbles are gone. Drip it from a spoon or syringe into a bath of water and calcium chloride or calcium lactate. A skin of gel forms on the outside only. Lift the spheres out and rinse off the calcium. Their skins are thin and break easily, so serve them at once.
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• Reverse. Drip a liquid that holds calcium into a bath of sodium alginate. A calcium alginate skin forms at once, but the setting stops at the skin and does not spread inward. The shells are thicker, so the spheres keep and need not be eaten straight away.
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Calcium lactate is often chosen over calcium chloride because it leaves no bitter taste.

The ingredients

Iota carrageenan is hydrated in cold liquid and then heated to about 70°C (158°F) while mixed hard; it sets anywhere from 40°C to 70°C (104–158°F), depending on how much calcium is present. Gellan gum starts to dissolve at 85°C to 95°C (185°F to 203°F). Kappa carrageenan gels melt back to liquid above 70°C (158°F).

Sous vide in the pastry shop

Sous vide, cooking food sealed in a bag in a water bath held at the food's target temperature, is covered in see chapter 10: How sous vide works. In the pastry shop it softens fruit and vegetables while keeping more of their vitamins and minerals than blanching or steaming does.