If done correctly
the boiled egg is one of the simplest ways to cook an egg. Since
it may be difficult to peel extremely fresh eggs, boiled eggs
are best with eggs that have already spent a few days in the refrigerator.
See below for a comparison of boiled egg to 'sous vide
peeling fresh eggs shells so difficult?
that are just a day or two old, the membrane beneath the shell
sticks tightly to the shell making peeling the egg almost impossible.
After a few days in the refrigerator the egg becomes easier to
is this? In fresh eggs the albumen sticks to the inner shell membrane
strongly than it sticks to itself because of the more acidic environment
of the egg. The white of a freshly laid egg has a pH between 7.6
and 7.9 and an opalescent (cloudy) appearance due to the presence
of carbon dioxide. After the protective coat is washed off the
egg shell the egg becomes
porous and begins to absorb air and loose some carbon dioxide
contained in the albumen. This reduces the acidity of the egg
which causes (after
several days in the refrigerator) the pH to increase to around
9.2. At higher pH the inner membrane does not stick as much to
the albumen so the shell peels off easier. In addition, as
the egg gets older it will shrink and the air space between the
egg shell and the membrane will get larger.
that the reduced acidity helps with peeling. The tradeoff, however,
is that in older eggs the yolk tends to move further from being
centered. This happens because the white gets thinner and is less
able to hold the yolk in place. The best compromise is to use
eggs that have been stored on their sides in the refrigerator
for 7 to 10 days.
Peeling Boiled Eggs :
What is the
best way to peel a boiled egg so the egg white does not stick
to the shell? Here are several responses, although all bets are
off for eggs only a couple days old.
After boiling, pour off the hot water, shake pan back and forth
to crack the shells. Cover eggs in cold water and let set for
a couple of minutes. Leave water and eggs in pan and peel, using
water to rinse away excess shells.
take the egg from boiling water and immediately run cold water
on it. Peel the egg under cold running water starting with rounded
top where the air pouch is.
eggs crack? How can I prevent eggs from cracking while boiling?
rounded end of an egg contains a small air bubble. As the egg
heats up, the air inside the bubble expands. As the hot air pushes
outwards, it puts pressure onto the shell, making it crack. You
can prevent this by making a pin-pick in the bottom rounded end
of the egg. This will let the expanding air escape.
You can also
prevent cracking by letting eggs come to room temperature before
cooking them. Add the eggs to tap water and then apply the heat.
Do not add eggs directly into boiling water.
salt or vinegar in the water will not prevent the egg from cracking
but will congeal the white if it starts to leak out of the shell
from a small crack, making the cracked egg, still pleasing to
Cooking Boiled Eggs
in a pot of cold water. To avoid cracking the eggs place them
in the pot with a spoon. Turn on the heat and wait until the water
has come to a boil. Cover the pot, then turn off the flame. Let
the pot sit with the cover on for the desired amount of time (see
of the egg at the start of the cooking process will affect the
cooking time. An egg that is at room temperature at the start
of the cooking process will require about 1 minute less cooking
time for each time listed above. The times listed above are based
on eggs taken directly from the refrigerator. Source
temperature do eggs set?
It is not
really necessary to keep the water boiling when cooking eggs
since the proteins in eggs coagulate well below 212°F. Egg whites
begin to thicken at 145°F/63°C and become a tender solid when
the temperature reaches 150°F/ 65°C (although ovomucin yolk cords
coagulate at much higher temperatures) . The yolk protein will
start to thicken at 150°F and set at 158°F/70°C. The whole egg
will set at around 165°F/73°C. If eggs are cooked at 212F for
too long they will just get rubbery as proteins continue to coagulate
and water gets pushed out from between protein molecules.
in mind salmonella is killed instantly when subjected to a temperature
of 160° F . An egg (white and yolk) requires a temperature of
up to 158°F before it sets properly. The white alone requires
a somewhat lower temperature before it coagulates, usually in
the 140° to 150°F range. These temperatures are only slightly
less than what is required to destroy all of the harmful bacteria
that may be present, so heating eggs to 160° F should not cause
eggs to be overcooked, unless they are held at that temperature
(or higher) for an extended period.
are the general temperatures at which various egg parts and egg
products will coagulate:
egg yolk 65-70°C
whole egg begins to become opaque at around 60° C and increases
in viscosity to 72° C. At 75° C it is a soft curd and increases
in firmness up to 87° C.
Eggs vs. Sous Vide Eggs
have claimed the perfect egg to be the 65 °C (145°F) egg where
both whites and yolk have similar consistencies. We have found
in our own tests that eggs still exhibit a runny white while the
yolk is more solid at these temperatures (see photos above and
below). As shown below the boiled egg exhibits a reverse effect
with the whites coagulating first compared to the sous vide egg.
Vide egg at 147F (1hr)
Runny whites and sem-solid yolk
8 minute boiled egg
Solid whites and runny yolk
For more details
on Sous vide eggs click
the green film on boiled eggs?
gray film will form on the surface of the yolk when the temperature
of the yolk exceeds 158° F. This discoloration is not unhealthful.
It's just a visual indicator of a natural chemical reaction. Sulfur
from amino acids in the white of your egg (or albumen) is reacting
with iron from the yolk which causes a film of ferrous sulphide
to form on the yolk's surface. If the film is thin, your egg will
still taste fine.
Heat speeds up this reaction, so the longer your eggs cook, the
greater the chance of discoloration. That's why it is best when
cooking hard boiled eggs to turn off the flame when the water
boils and let the egg sit for 17 minutes in the hot water bath
with the lid on. Then plunge the egg into cold water.
eggs too old -- How to Test for Egg Freshness
As an egg
ages it gets lighter by evaporation of water through the porous
shell, causing the growth of the air space. A fresh egg is heavy
and should feel well filled. Hence the old water test for freshness,
a fresh egg sinks and an old egg floats. When broken, the white
of a fresh egg should be compact round the yellow. It spreads
out, as it gets older. Holding it up to the light can also test
the freshness of an egg. A very small air chamber indicates a
very fresh egg. Typically eggs reach the shops within 2-3 days
of being laid. Eggs should be used within 1 month and kept under
the conditions described.
ALSO: HOW FRESH IS THAT EGG?
In normal, "non" salted water, an egg that lays on the
bottom is fresh. An egg that stands on end is still useable. And
egg that floats is rotten.
age there is an increase in yolk size, thinning of the egg white,
weakening of vitellenin membrane and deterioration of odor and
flavor. The deterioration depends upon the storage conditions.