Tomato Anatomy and Flavor

Aside from the relatively dry paste varieties, most tomatoes have four different kinds of tissue: a thin, tough cuticle, or skin, which is sometimes removed; the outer fruit wall; the central pith; and a semiliquid jelly and juice surrounding the seeds. The wall tissue contains most of the sugars and amino acids, while the concentration of acid in the jelly and juice is double that of the wall. And most of the aroma compounds are found in the cuticle and wall. The flavor of a tomato slice thus depends on the relative proportions of these tissues. Many cooks prepare tomatoes for cooking by first removing the skin, seedy jelly, and juice. This practice makes the tomato flesh more refined and less watery, but it changes the flavor balance in favor of sweetness, and sacrifices aroma. The tomato’s citric and malic acids aren’t volatile and don’t cook away, so acidity and some aroma can be restored by cooking the skins, jelly, and juice together until much of the liquid has evaporated, then straining the remainder into the cooking tomato flesh. As cooks have long known and flavor chemists have verified, the overall flavor of tomatoes can be intensified by the addition of both sugar and acidity.