On Food and Cooking

especially prominent in fruits and vegetables.
Sugar is the main product of photosynthesis,
and its sweetness is the main attraction
provided by fruits for their animal seed
dispersers. The average sugar content of ripe
fruit is 10 to 15% by weight. Often the unripe
fruit stores its sugar as tasteless starch, which
is then converted back into sugar during
ripening to make the fruit more appealing. At
the same time, the fruit’s acid content usually
drops, a development that makes the fruit
seem even sweeter. There are several organic
acids — citric, malic, tartaric, oxalic — that
plants can accumulate in their vacuoles and
variously use as alternative energy stores,
chemical defenses, or metabolic wastes, and
that account for the acidity of most fruits and
vegetables (all are acid to some degree). The
sweet-sour balance is especially important in
fruits.
Most vegetables contain only moderate
amounts of sugar and acid, and these are