I have a personal vendetta against gelled foods. Some of the most delicious sweets – Jell-O, marshmallows, custards, and gummy bears – get their springy texture from meat-based gelatin. I’m a vegetarian, which means I’m always left sulking while others are enjoying.
One technique used widely in molecular cooking is gelification – making food into gels. Happily for me, molecular gastronomists have begun to use all sorts of vegetarian substances to give food a jelly-like texture. In addition to gelatin chefs are using agar, pectin, carageenans, alginates, xanthan gum, and other substances with similar properties to make foods springy.
At a molecular level, a gel is an interesting combination of liquid and solid. When you shake a plate with a block of Jell-O on it, the gel wriggles like a liquid, but retains it shape like a solid. All gels have a scaffold-like solid matrix that holds them up, with liquid molecules that are trapped among the solid building blocks. By weight, liquid makes up most of the gel.
In food gels, the solid matrix is usually made up of carbohydrates or proteins. In agar-agar, for example, the gelling agent is a carbohydrate derived from a certain species of red algae. When making a gel, agar-agar powder is added to a liquid and mixed well. Heating up the mixture allows the agar-agar sugar subunits to absorb the liquid around them. The solid agar-agar units unfurl to form a structure with liquid trapped inside it. As the mixture cools, the sugars become more rigid, remaining suspended and therefore distributed evenly throughout the liquid.
Like agar-agar, starch expands in water as it's heated. When the substance is cooled, starch remains in its unfurled, rigid configuration. This is why cornstarch can be used as a thickening agent. // By Avi Saig
Usually, solids floating in liquids sink to the bottom. But in gels, solids stay suspended. The reason has to do with intermolecular forces. Miniscule charges on the individual solid particles keep them spaced apart, one from another. Because they can’t get too close, they don’t aggregate at the bottom. The general term for substances in which solids are suspended is “hydrocolloid.”
Using hydrocolloids, chefs are creating all sorts of novelties. They have made spaghetti that falls right in the texture sweet spot, neither under- nor over-cooked. Because various hydrocolloids turn into gels at different temperatures, chefs have been able to create outlandish concoctions that would have been impossible using only traditional ingredients like gelatin and egg whites. For example, one chef has created hot ice cream, which apparently tastes and feels like ice cream, but exists at the complete opposite end of the temperature spectrum. Another chef has created hot and cold tea. Using a gelling agent, he creates a partition to separate two sides of a cup. He fills one side with iced tea, and the other side with hot tea. The drinker can then drink both hot and cold tea at the same time – quite the culinary experience.
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