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
are peeling fresh eggs shells so difficult?
eggs 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 peel. Why
is this? In fresh eggs the albumen sticks to the inner shell membrane
more 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.
shows 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.
on Peeling Boiled Eggs :
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
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.
do eggs crack? How can I prevent eggs from cracking while boiling?
bottom, 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.
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.
either 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 look at.
on 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
temperature 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
what temperature do eggs set?
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.
Keep 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
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
causes the green film on boiled eggs?
greenish 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.
these eggs too old -- How to Test for Egg Freshness
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.
eggs 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.