Appears in
On Food and Cooking

By Harold McGee

Published 2004

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We’ve seen that the texture of vegetables and fruits is determined by two factors: the inner water pressure of the tissue’s cells, and the structure of the cell walls. Cooking softens plant tissues by releasing the water pressure and dismantling the cell walls. When the tissue reaches 140°F/60°C, the cell membranes are damaged, the cells lose water and deflate, and the tissue as a whole goes from firm and crisp to limp and flabby. (Even vegetables surrounded by boiling water lose water during cooking, as weighings before and after will prove.) At this stage, vegetables often squeak against the teeth: they’ve lost the crunch of turgid tissue, but the cell walls are still strong and resist chewing. Then as the tissue temperature approaches the boiling point, the cell walls begin to weaken.The cellulose framework remains mostly unchanged, but the pectin and hemicellulose “cement” softens, gradually breaks down into shorter chains, and dissolves. Teeth now easily push adjacent cells apart from each other, and the texture becomes tender. Prolonged boiling will remove nearly all of the cell-wall cement and cause the tissue to disintegrate, thus transforming it into a puree.