Like other starchy winter vegetables such as squash, potatoes
store well because of their low moisture content and thick
skins. If the tubers don’t have any blemishes and
are stored in a cool place away from light, they can last
a long time.
Under a microscope, the starch granules packed inside
the potato cells appear as smooth oval shells. When you
bake a potato, the starch granules absorb the moisture
within the potato. Within the confines of the potato skin,
moisture soon turns to steam that expands with great force,
separating the starch granules and making a fluffy baked
potato. If there’s sufficient pressure, and the
skin hasn’t been pierced before baking, the potato
may even explode in the oven!
In contrast to oven baking, when potatoes are boiled the
starch granules absorb not only the internal moisture
but also some of the surrounding water. Extra water contributes
to making potatoes gummy when mashed. To avoid this problem,
once the potatoes are boiled, drain them well, return
them to the pot, cover, and place them back briefly on
the warm element to evaporate some of the excess moisture.
When making mashed potatoes, be careful not to mix them
too long or too vigorously. This causes the starch granules
to rupture and spill their moist starchy contents, resulting
in mashed potatoes that are wet and pasty. Some cooks
claim that heating milk or butter before adding them to
mashed potatoes can make for a more pleasing texture in
the finished dish.