Green Eggs: The Science of Egg Cookery
Have you seen hard-boiled eggs with a greenish-gray ring around the
yolk? Did you wonder what it was? Is it harmful? How do you avoid it?
Although the greenish ring around the yolk is unappealing, it is not
harmful and it does not affect the flavor of the egg. It is caused by
a natural chemical reaction between compounds in the yolk and the white,
and it is only formed when eggs are heated.
The Science of Egg Cookery
The egg yolk contains iron and the white (albumen) contains sulfur.
During boiling the sulfur atoms are liberated and react with hydrogen
ions in the white to form hydrogen sulfide (a gas). As gas forms, it
diffuses in all directions and some reaches the surface of the yolk,
where it encounters iron and reacts to form dark particles of ferrous
sulfide (FeS).
The way to minimize the discoloration is to minimize the amount of
hydrogen sulfide that reaches the yolk. When preparing hard-cooked eggs,
use proper cooking times and temperatures, do not cook eggs in boiling
water, do not use an iron pot, cool cooked eggs rapidly in cold water
and peel them promptly.
Hard Cooked Eggs
Most people do not know how to make hard-boiled eggs. The term "hard
boiled egg" is the killer. It implies the need to cook eggs in
rapidly boiling water for a long time. If this is your method, you are
probably producing green rubbery eggs consistently. Eggs, in fact, do
not need to boil, which is why the American Egg Board no longer uses
the term "hard boiled." Holding eggs in hot water for 15 minutes
will cook the white and produce a firm yellow yolk. See "To Hard
Cook Eggs" in Health & Household Tips of this issue.
Hard cooked eggs will keep safely in the refrigerator for one week.
Remember cooked eggs are perishable and should not be left at room temperature
for more than two hours - including Easter eggs.
Spring
2001
Finding the Best Site for a Garden Is More Than a
Random Process | Build a Raised Bed |
It Takes a Kernel of Skill to Grow Great Sweet Corn | Pruning
Ornamentals Keeps Your Garden on the Cutting Edge | Lawn
Care Calendar | Hort Shorts | Hort
Tips | Mad Cow Disease | Green Eggs: The Science
of Egg Cookery | Concern for Egg Safety | New
National Standards for Organic Food | Your Spring
Vegetable Garden Plan | Health & Household Tips
| Did You Know?
Index
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