On Food and Cooking

firm during hours of cooking, while in neutral
boiling water, neither acid nor alkaline, the
same vegetables soften in 10 or 15 minutes. In
distinctly alkaline water, fruits and vegetables
quickly become mushy. Table salt in neutral
cooking water speeds vegetable softening,
apparently because its sodium ions displace
the calcium ions that cross-link and anchor
the cement molecules in the fruit and
vegetable cell walls, thus breaking the cross-
links and helping to dissolve the
hemicelluloses. On the other hand, the
dissolved calcium in hard tap water slows
softening by reinforcing the cement cross-
links. When vegetables are cooked without
immersion in water — when they’re steamed
or fried or baked — the cell walls are exposed
only to the more or less acid cell fluids (steam
itself is also a somewhat acidic pH 6), and a
given cooking time often produces a firmer
result than boiling.