remove water and concentrate it, the high temperatures break the already enzymedamaged molecules into smaller pieces that are less efficient thickeners, and the paste requires that much greater reduction to obtain the desired thickness If instead the raw puree is cooked quickly close to the boil, the result is a thicker sauce that requires less subsequent reduction The pectin and cellulose enzymes are denatured and become inactive, while at the same time the cell walls are disrupted by the heat The cell-wall pectins that escape into the fluid phase during the concentration heating are longer molecules and more efficient thickeners The Thickening Components of Tomatoes Total Solids, Pectin and Hemicellulose % by weight Content, % by weight Raw tomatoes 5–10 0.5–1.0 Canned tomato puree 8–24 0.8–2.4 Canned tomato paste 40 Tomato Enzymes and Flavor In addition to tomato enzymes that affect texture, there are enzymes that affect flavor: and in the case of flavor, some initial enzyme activity can be desirable The fresh, “green”-smelling molecules (hexanal and hexanol, p 274) that are an important element in ripe tomato flavor are generated by the action of enzymes on fatty acids when the fruit tissue is crushed, either in the mouth or in the pot Rapid cooking to the boil minimizes this fresh flavor element, while allowing the raw puree to sit at room temperature — in a Mexican salsa, for example — or only slowly heating it, will cause the accumulation of these flavor molecules in the puree A method that home cooks sometimes use is to halve or quarter tomatoes, then bake them in a slow oven to remove water, and finally cook them relatively quickly into a sauce This technique ... molecules (hexanal and hexanol, p 274) that are an important element in ripe tomato flavor are generated by the action of enzymes on fatty acids when the fruit tissue is crushed, either in the mouth or in the pot... example — or only slowly heating it, will cause the accumulation of these flavor molecules in the puree A method that home cooks sometimes use is to halve or quarter tomatoes, then bake them in a slow oven to remove water, and finally cook them... Tomato Enzymes and Flavor In addition to tomato enzymes that affect texture, there are enzymes that affect flavor: and in the case of flavor, some initial enzyme activity can be desirable The fresh, “green”-smelling