why is the yolk always in the center of a hard boiled egg?

[sixto]

An 8 year old asked me and I couldn't answer - why is the yolk always in the center of a hard boiled egg?

Sixto
87 300D

[Carson357]

who is to say that until it is opened that it isn't always in the center? i am also thinking that the white may keep it from contacting the shell

http://books.google.com/books?id=qO-e-JFViVYC&pg=PA29&lpg=PA29&dq=why+is+the+yolk+always+in+the+center+of+a+hard+boiled+egg%3F&source=web&ots=eP9AGXhm-e&sig=DwKNockpLtUi9lkomdF3v5bk5v0&hl=en&sa=X&oi=book_result&resnum=1&ct=result

[Chas H]

Originally Posted by sixto

An 8 year old asked me and I couldn't answer - why is the yolk always in the center of a hard boiled egg?

Sixto
87 300D

It's not always in the center. If an egg is stored properly-small end down- before cooking, the yolk will be close to the center. If not, the yolk will be off center.

[Chad300tdt]

I was going to say the same thing. Any time I make deviled eggs, at least 3 per dozen are so off center that half the egg can't hold the filling due to being too thin.

[The Clk Man]

Originally Posted by Chad300tdt

I was going to say the same thing. Any time I make deviled eggs, at least 3 per dozen are so off center that half the egg can't hold the filling due to being too thin.

A debt, owed.

[MTI]

For years, I must have been doing it wrong.

The Food Lab: The Hard Truth About Boiled Eggs | Serious Eats

My previous method was to start in cold water, get to a boil and then cover and kill the heat for 15 minutes, then shock in ice water till chilled all the way. Now, I gotta try steam.

[Botnst]

There is a membrane that fits snugly against the shell. If you look closely at a raw egg carefully opened with the young and 'white' intact, you'll notice some gelatinous threads. You might have to move the egg white around a bit to notice the difference. Also, if you whisk an egg the strands are the part that won't let go of the whisk, kind of like a bobby strand of snot.

Those floppy, gelatinous strands help keep the egg yolk centered when the egg is laid on its side, which how they sit on the hen's nest. Without those two strands the egg would heat and cool differently depending on orientation, which would be bad for embryogenesis.

For example, a lot of reptiles will die if the egg is not kept properly centered and oriented.

[elchivito]

Originally Posted by Botnst

There is a membrane that fits snugly against the shell. If you look closely at a raw egg carefully opened with the young and 'white' intact, you'll notice some gelatinous threads. You might have to move the egg white around a bit to notice the difference. Also, if you whisk an egg the strands are the part that won't let go of the whisk, kind of like a bobby strand of snot.

Those floppy, gelatinous strands help keep the egg yolk centered when the egg is laid on its side, which how they sit on the hen's nest. Without those two strands the egg would heat and cool differently depending on orientation, which would be bad for embryogenesis.

For example, a lot of reptiles will die if the egg is not kept properly centered and oriented.

This, plus the fact that a setting hen will turn the eggs every few hours. They're pretty meticulous about doing it. The yolk is the embryo's food supply. It shrinks as the chick grows. Commercial mechanical incubators do it automatically.