On IO9, Esther Inglis-Arkell does a great job of describing the molecular gastronomy practice of "spherification," whereby food is liquefied and then coaxed into forming gelatinous spheres. It has its origin in a 1950s drug-delivery project from Unilever, but was revived by chef Ferran Adrià around 2003.
What spherification does is put back in what the manufacturers of sodium alginate take out. First, the food, whatever it is, is pureed until it's liquid. Then the calcium content of the food is determined. If the calcium content is high, adding sodium alginate will solidify the whole thing immediately. To high-calcium foods extra calcium chloride is added. To all other foods, sodium alginate is added. Then, as with all delectable meals, it's off to the centrifuge. The mixture gets centrifuged to remove any bubbles or impurities there might be in it. Once that's done, drops of the stuff are tossed into a bowl of liquid. If the food contains calcium chloride, the liquid will contain sodium alginate. If the food contains alginate, it will be tossed into liquid containing calcium.
Immediately, the process begins. The outer edge of the spherical drops is the front line. When the sodium alginates hit calcium ions, the ions bind the long strings together, until they form a kind of haphazard net of polymers. The outer layer of the gel solidifies before any of the inner liquid can leak out. Depending on the concentration of both chemicals, and the time spent in the 'bath,' the gel will either be a tiny skin, or an extremely firm layer. Even if the mix of chemicals is weak, the reaction will keep moving inwards, so the balls have to be whisked carefully out of the bath, put on a plate, and rushed out to be set in front of the strained smiles of dinner guests. Then there's just enough time to say, "Oh. You served me vegetable soup in cold, quivering ball form. How original," and it's down the reluctant hatch.
Better living through chemistry.
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