You must be referring to the New York Times article from 2006, The Way We Eat: Which Came First?
According to the author, you need a few elements in order for this to work:
Make sure you use only the "thick whites". That means either using farm-fresh eggs, or straining away the "thin whites" with a slotted spoon after cracking the eggs.
Beat the eggs with a fork (not a whisk), and don't add salt, because the grains will tear the eggs.
Create a whirlpool in the boiling water (low boil, not rolling), which is basically to help the eggs stay suspended instead of sinking to the bottom.
According to him, the eggs take about 20 seconds to cook, after which you should strain them.
Note: Personally, I haven't tried this. I don't know about you, but in my kitchen, it usually takes less time to make scrambled eggs in a non-stick pan than it does to boil water. It would appear that this technique was developed due to some completely unfounded concerns about the safety of non-stick pans. If you are still worried about safety after reading that, or just feel like experimenting, then by all means try it out. I'm just including this little disclaimer because the NYT article gives a lot of airtime to the rumours and not much to the facts.
Good question @mfg. I hope I can help a little bit. The basics behind the egg wash are to provide for a couple different thing. These being shine, crispness, and color.
Shine
The shine is primarily provided by the egg yolk. The higher concentration of yolk the more shine.
Crispness
This come from the egg whites. The whites make things a little crispy and sometimes can crackle a little bit (mainly when usually by themselves).
Color
This comes from the fat and protein. Leaving the yoke in along with the shine will add color. You can add water to lighten the color a bit. I find that using the white also dilutes the color a bit but not as much (but the white also makes it crisp). Add cream or milk to get it a little bit darker.
Salt
I often find people adding salt to an egg wash. I does provide some flavor to the crust, but I have noticed that for some reason (when using a whole egg) it does allow it to get a little darker than it would normally.
Sugar
Like salt it adds flavor (sweetness) to the crust. And it will also add some color. Especially if baking at a higher temp and using a raw or brown type sugar.
Alcohol
I have seen the use of alcohol quite a number of times. From the results I have seen it behaves like water. Although not the the same degree. My guess is that it has to do with how fast the alcohol evaporates. As far as flavor, I can't say that it added much at the levels used. I did once definitely get a hint of a bourbon being used in the wash on a pretty plain white loaf. But they did mix in quite a good amount of bourbon to just an egg yolk.
That is all I have really used myself or seen. I am sure that you can use other liquids although I don't know what vinegar would do. Just keep in mind if they are high in fat, protein, or sugar they will add color. Otherwise they will lighten the color.
I have also seen melted butter just used as a wash. It adds a nice color and buttery flavor. I haven't seen it added to egg wash but I would assume you could add to egg yolk to get a shine and probably darker color than cream/milk.
Another important thing to remember is to beat your wash well when using for a bread coating. Unlike if your just using the was was to seal say a ravioli. If your egg was is spotty not one nice fully incorporated mixture your crust can also be spotty.
Best Answer
A 63-degree egg is slow cooked in the shell in a water bath of 63 degrees celsius. The shell is removed after the cooking process. A poached egg is removed from the shell before cooking and cooked in simmering water for a short amount of time. According to this experiment, cooking eggs at slightly different temperatures in a water bath seems to make a difference. Perhaps the more exact cooking temperatures of a 63 degree egg give it a different texture than a regular poached egg.