On Food and Cooking

is so extreme that the walls have practically
disintegrated, and the watery cell interior
oozes out under the least pressure. The
contents of the cells also have an effect: a ripe
fruit’s vacuole full of sugar solution will give
a melting, succulent impression, while a
potato’s solid starch grains will contribute a
firm chalkiness. Because starch absorbs water
when heated, cooked starchy tissue becomes
moist but mealy or pasty, never juicy.
The changes in texture that occur during
ripening and cooking result from changes in
the cell-wall materials, in particular the
cement carbohydrates. One group is the
hemicelluloses, which form strengthening
cross-links between celluloses. They are built
up from glucose and xylose sugars, and can be
partly dissolved and removed from cell walls
during cooking (p. 282). The other important
component is the pectic substances, large
branched chains of a sugar-like molecule
called galacturonic acid, which bond together