Food chemistry - beating eggs
Jude
certain ingredients react the way they do in cooking. So here's my
question.
What changes in an egg if you beat it for a long time? Specifically, I
made an upside-down cake the other day. The recipe stated, "Beat 2 egg
yolks for 5 minutes, until thick and lemon yellow." Thises then get
sugar, flour, juices, etc added for cake batter.
Also, I have a recipe for a non-baked creamy pie filling that states,
"Add 1 egg. Beat for 2 minutes. Add second egg. Beat for 2 minutes."
This is a filling that is made of butter, sugar, cocoa and instant
coffee flakes. No, the eggs never get cooked. Yes, I know about
salmonella risk. But thats not the point; it was grandma's recipe and
I'm gonna make it and eat the darn raw eggs.
What changes when you beat an egg for longer, rather than just a short
turn with the mixer to combine white and yolk, or froth it a bit? And
what happens that causes the yolks to look so thick and lemony after 5
minutes of beating?
Thanks for tellig me in plaing English. I'm not a pro chef, just a
curious home baker.
Charles Quinn
@j33g2000cwa.googlegroups.com:
A slightly beaten egg is used to thicken or bind ingredients, and
increases volume when scrambling eggs or cooking omelets. One-half minute
of brisk beating with a fork or egg whisk is adequate for the purpose.
Test the results by lifting the fork with adhering egg. If the egg flows
from the fork easily and contains only a few air bubbles, it is slightly
beaten.
A well beaten egg used for leavening is best performed using a rotary
hand beater or electric mixer. Beat the egg until it is very frothy and
changes to a white or light cream color. Egg yolk is thoroughly beaten
when it becomes thick and has a uniform lemon color. A description of
various egg beating stages as indicated in recipes are as follows.
Slightly beaten white is used to clarify, emulsify, and thicken solutions
or in used in coating for meats and baked dishes. When beat for one-half
minute, the white is slightly foamy but is still transparent and flows
easily.
Stiff foam white is used in meringues that require a shiny, glossy and
moist albumen. When the beaters or whisk is withdrawn, the albumen
follows to form rounded peaks.
Stiff white is used in hard meringues, cakes, omelets, cooked frostings,
candies, and marshmallows. Properly beat stiff white is no longer foamy
and does not stick to the bowl when tipped, but remains glossy, smooth
and moist.
From http://www.msstate.edu/dept/poultry/4heggs.htm
--
Charles
The significant problems we face cannot be solved
at the same level of thinking we were at when we
created them. Albert Einstein
chembake
>made an upside-down cake the other day. The recipe stated, "Beat 2 egg
>yolks for 5 minutes, until thick and lemon yellow." Thises then get
>sugar, flour, juices, etc added for cake batter
If you beat longer there will come a time that the protein/ fat/sugar/
water emulsion will breakdown. There is a limit where the egg protein
structure will entrap gas bubbles...As more air is incorporated it
tends to dry up the moisture in between the bubbles which is one cause
for bubbles to merge together increasing its diameter. The weakening of
the pore cell structure is also brought about by the thinning of the
protein membrane that entrap the bubbles. Another cause is emulsion
destabilization etc...
>What changes when you beat an egg for longer, rather than just a short
>turn with the mixer to combine white and yolk, or froth it a bit? And
>what happens that causes the yolks to look so thick and lemony after 5
>minutes of beating?
When eggs is beaten the protein structure entrap gas bubbles; the more
you beat it the finer the bubble size due to subdivision of the
original bubble size but there is a limit, more beating will lead to
drying which makes the foam stiff and becoming rigid and unable to
expand. The moment you fold in the other ingredients it will interrupt
the fragile bubble structure which is not flexible anymore due to lack
of moisture.
Therefore if you incorporate dry ingredients to an overbeaten foam it
will result in poor volume cakes.
Whereas if the eggs are beaten optimally say until medium peak to stiff
but not dry there is still enough moisture for it to remain flexible
where you can add other ingredients .
If you beat it only slightly like scrambled eggs the fat in the egg
yolk will tend to inhibit the formation of a water in oil emulsion
(rather the reverse it will form a oil in water emulsion that is not
prone to aeration )lessening the formation of air bubbles .
But if you insist in beating for a long time( specially in the presence
of sugar such as in sponge cake recipes) the emulsion will gradually
stabilze as the fat component of the egg protein will be emulsifyied
by the lecithin component with the available water ( in egg)forming a
lipoprotein- glycoprotein complex. The sugar due to dissolution in
water will increase the viscosity allowing the protein to form a film
which will enable it to form bubbles.
As the fat tends to have weakening effect on the bubble structure, you
will see that the nature of the whole egg protein foam is not as stiff
as the egg white protein foam( in meringue)
Overbeating will lead to gradual foam breakdown which will led the
small bubbles to merge making larger bubbles which led to the reduction
of air pressure but the increase of unit bubble volume. As the pressure
is not that strong anymore the foam structure is weaker and it cannot
support the expansion of the batter to optimum volume.
Physically the increase in bubble diameter results in increase of
specific gravity *(or thinning of the batter in cakes).
chembake
>If you beat it only slightly like scrambled eggs the fat in the egg
>yolk will tend to inhibit the formation of a water in oil emulsion
>(rather the reverse it will form a oil in water emulsion that is not
>prone to aeration )lessening the formation of air bubbles .
It should be
it will tend to inhibit the formation of oil in water emulsion but
rather the reverse, water in oil emulsiom which is not conducive to
foaming..
But when beaten more specially in the presence of sugar, the emulsion
will gradually stabilize as more moisture is bound by the sugar making
it viscous liquid that promote the protein to foam.
Further
The resulting emulsion will be more stable as the balance of water is
kept in check by the sugar and destabilization of the foam is reduced.
There is still the presence of the lipoprotein- glycoprotein solution
complex in the egg, sugar, water combinatikon that helps in the
stabilization.