Most sweet potato varieties sweeten during
cooking thanks to the action of an enzyme that
attacks starch and breaks it down to maltose, a
sugar made up of two glucose molecules
that’s about a third as sweet as table sugar.
Moist or “soggy” varieties convert as much as
75% of their starch to maltose, so they seem
permeated with syrup! The enzyme starts to
make maltose when the tightly packed starch
granules absorb moisture and expand,
beginning around 135ºF/57ºC, and it stops
when the rising heat denatures it, at around
170ºF/75ºC. Slow baking therefore gives the
enzyme a longer time to work than does rapid
cooking in steam, boiling water, or a
microwave, and produces a sweeter result.
Freshly harvested “green” roots available in
the autumn have less enzyme activity and so
don’t become as sweet or moist.
Pale and red-purple sweet potatoes have a
delicate, nutty aroma, while orange types have
the heavier, pumpkin-like quality created by
barry
(Barry)
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