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Chemistry Of Cooking
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January 1, 2009 — A biochemist and cook explains that cooking is all about chemistry
and knowing some facts can help chefs understand why recipes go wrong.
Because cooking is essentially a series of chemical reactions, it is
helpful to know some basics. For example, plunging asparagus into
boiling water causes the cells to pop and result in a brighter green.
Longer cooking, however, causes the plant's cell walls to shrink and
releases an acid. This turns the asparagus an unappetizing shade of
grey.




You love to cook, but have you whipped up some disasters? Even the
best recipes can sometimes go terribly wrong. A nationally recognized
scientist and chef says knowing a little chemistry could help.
Long before she was a cook, Shirley Corriher was a biochemist. She
says science is the key to understanding what goes right and wrong in
the kitchen.
"Cooking is chemistry," said Corriher. "It's essentially chemical reactions."
This kind of chemistry happens when you put chopped red cabbage into a
hot pan. Heat breaks down the red anthocyanine pigment, changing it
from an acid to alkaline and causing the color change. Add some vinegar
to increase the acidity, and the cabbage is red again. Baking soda will
change it back to blue.
Cooking vegetables like asparagus causes a different kind of reaction when tiny air cells on the surface hit boiling water.
"If we plunge them into boiling water, we pop these cells, and they suddenly become much brighter green," Corriher said.
Longer cooking is not so good. It causes the plant's cell walls to shrink and release acid.
"So as it starts gushing out of the cells, and with acid in the
water, it turns cooked green vegetables into [a]yucky army drab,"
Corriher said.
And that pretty fruit bowl on your counter? "Literally, overnight you
can go from [a]nice green banana to an overripe banana," Corriher
said.
The culprit here is ethylene gas. Given off by apples and even the
bananas themselves, it can ruin your perfect fruit bowl -- but put an
apple in a paper bag with an unripe avocado, and ethylene gas will work
for you overnight.
"We use this as a quick way to ripen," Corriher said. Corriher says understanding a little chemistry can help any cook.
"You may still mess up, but you know why," she said. When it works, this kind of chemistry can be downright delicious.


WHAT ARE ACIDS AND BASES? An acid is
defined as a solution with more positive hydrogen ions than negative
hydroxyl ions, which are made of one atom of oxygen and one of hydrogen.
Acidity and basicity are measured on a scale called the pH scale. The
value of freshly distilled water is seven, which indicates a neutral
solution. A value of less than seven indicates an acid, and a value of
more than seven indicates a base. Common acids include lemon juice and
coffee, while common bases include ammonia and bleach.
WHY DOES FOOD SPOIL? Processing and improper storage practices can
expose food items to heat or oxygen, which causes deterioration. In
ancient times, salt was used to cure meats and fish to preserve them
longer, while sugar was added to fruits to prevent spoilage. Certain
herbs, spices and vinegar can also be used as preservatives, along with
anti-oxidants, most notably Vitamins C and E. In processed foods,
certain FDA-approved chemical additives also help extend shelf life.
This report has been produced thanks to a generous grant from the Camille and Henry Dreyfus Foundation, Inc.
Mr. Densign
 
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