On Food and Cooking

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.
Tomatoes that are allowed to ripen fully on
the vine accumulate more sugar, acid, and
aroma compounds, and have the fullest flavor.
An important element of ripe-tomato flavor is
provided by the aroma compound furaneol,
which resembles sweet-savory caramel (it