A lot of recipes that call for separating an egg, suggest that the egg be separated when cold rather than at room temperature even if it has to be brought to room temperature afterwards. I was just wondering what makes it easier to separate eggs when cold and if there is a chemical reason or the cells of the egg change under different temperatures? What's the science behind it?
Eggs – Why is it easier to separate a cold egg
eggsfood-science
Related Solutions
The traditional method is as Rumtscho describes.
I got tired of this method for several reasons:
- Egg shells are dirty.
- Shells get in the egg (especially with home collected eggs which have MUCH thicker shells than store purchased eggs)
- Egg shells are sharp and it's hard to keep yolks whole.
- That method just takes too long if you need more than 2 eggs.
Now I just crack the egg into my hand (which has been thoroughly washed -- cleaner than an eggshell). I hold my fingers a little apart and let the white slip through, leaving the yolk in my hand.
Quick and simple.
Regardless of the method that you use you should use three bowls: one for the collected whites, one for the white you are working on, and one for the yolks.
Remember: only dump the current white into the collected whites after verifying that the yolk is whole. That way you don't spoil all your whites with one broken yolk.
This is the nature of meringue: they will start to fall apart as soon as you stop whipping. There are a few tricks to help it hold longer, but in general you want to have EVERYTHING ready to go as soon as the meringue is whipped.
To help stabilize the meringue you can:
- Use a copper or SILVER-plated bowl to whip, or add a tiny amount of powdered copper supplement from a health food store
- Acidify it slightly: add 1/8 tsp cream of tartar or 1/2 tsp lemon juice per white, before beating
- Let the bowl warm to room temperature, which increases the ability of the whites to take in air
- Ensure there is absolutely no yolk in with the whites. The fat greatly destabilizes the foam.
Now for WHY these tricks work:
I'm going to quote heavily from Harold McGee's "On Food and Cooking", as it does a wonderful job explaining meringues and other whipped egg whites:
Like the head on a beer or a cappucino, an egg foam is a liquid--the white--filled with a gas --air-- in such a way that the mixuture of liquid and gas keeps its shape, like a solid. It's a mass of bubbles, with air inside each bubble, and the white spread out into a thin film to form the bubble walls. And the makeup of these liquid walls determines how long a foam can stand up. Pure water has such a strong surface tension--such strong attractive forces among its molecules--that it immediately starts to pull itself together into a compact puddle; and it's so runny that it puddles almost immediately. The many nonwater molecules in egg white both reduce the surface tension of the water they float in, and make it less runny, and thus allow the bubbles to survive long enough to accumulate in a sizeable mass. What gives the mass of foam a useful kitchen lifetime is the white's team of proteins.
Whisking unfolds these proteins, primarily globulins and ovotranferrin, which bond to each other and stabilize the bubble walls. Cooking will evaporate the water and unfold ovoalbumin, creating a rigid and permanent protein network.
However, the same proteins can ALSO destabilize the foam if they bond too tightly. "The protein network begins to collapse when too many of these bonds accumulate and the proteins cluster together too tightly" (page 102). In the case of egg proteins, one of the strongest bonds is a disulfide bond between the sulfur-containing amino acids, cysteine and methionine. Eggs contain copious quantities of these amino acids, which are why they produce such a potent stench when they spoil; the sulfur is converted to malodorous sulfur compounds, particularly hydrogen sulfide.
Copper, silver, and acids stabilize the egg foam by preventing the formation of these disulfide bonds. To quote Harold McGee (page 103):
It turns out that along with a few other metals, copper has the useful tendency to form extremely tight bonds with reactive sulfur groups: so tight that the sulfur is essentially preventing from reacting with anything else. So the presence of copper in foaming eggs whites essentially eliminates the strongest kind of protein bond that can form, and makes it harder for the proteins to embrace each other too tightly.
McGee also notes that silver has the same property of inhibiting disulfide bonding. Acid achieves the same goal of reducing disulfide bonding, but works slightly differently:
The sulfur bonds form when the sulfur-hydrogen (S-H) groups on two different protein molecules shed their hydrogens and form a sulfur-sulfur (S-S) connection with each other. The addition of an acid boosts the number of free-floating hydrogen (H) ions in the egg white, which makes it much harder for the S-H groups to shed their own H, and so slows the sulfur bonding down to a crawl.
Related Topic
- Eggs – Why do egg dye recipes include vinegar
- Eggs – Why or why not beat an egg before adding
- Eggs – Water vs. milk/cream (or nothing) in traditional (French) omelets
- Bread – Effects of elevated storage temperature on bread quality
- Eggs – the reason to coddle an egg
- What’s the point of hot food
- Baking – When to bring eggs whites to room temperature
Best Answer
It's a simple matter of viscosity, when eggs are cold the white is less runny. When eggs are warm the white is much more runny.
As for whether it is easier to separate eggs when cold or warm it depends on your method. If you use the shells to separate the white, by cracking them in half and then transferring the yolk back and forth between the halves, then I'd say cold is a bit better because once the white starts to drip out it tends to go as a whole. With warm eggs more white will stay in the shell with the yolk.
However, if you use your hands to separate the eggs, by letting the white drip between your fingers (or using an egg separator which does the same thing), warm eggs work much better because the runniness allows them to flow easier. This method works fine for cold eggs too, but warm is faster.
Of the two methods I prefer using my hands rather than the shell for a few reasons:
A handy trick if you are separating a lot of eggs is to separate each white into a separate bowl, then putting the white into a larger bowl with the rest of them. This is so if you get a bad egg, or a yolk breaks into the white you can discard the egg and keep the rest of them.