Saw Bobby Flay using vinegar to poach an egg, but I am not sure what it does to the egg. Any idea?
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The theory is that is helps keep the egg whites from spreading around the water. Add it to the water when it simmers, give it a quick stir, drop eggs. Plain distilled vinegar is the usual choice.
I say theory because no one has ever proven this. We tried to test it in class, but the results were negligible. It really matters what temperature the water is at.
The vinegar aides in coagulating the egg white. Although you need to remind yourself that a little vinegar goes a long way. I've used white, cider and even red wine vinegar in a pinch...balsamic was not a good choice.
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Yes, white vinegar is the best approach and add it just when the water hits the simmer point and then let the water come back to a simmer. Also use a fairly deep pot as this will help coax the albumen (egg white) to lift up and surround the yolk.
Harold McGee's technique is totally reliable, and doesn't require any acid added to the water. Tip your raw egg into a slotted or perforated spoon, and allow the thin albumen to drain away. When it does, you'll have just the thick part of the egg white and the yolk left. Slide that into your poaching water, and 3-4 minutes later: perfect poached egg, and no egg-drop-soup-ish mess. Works every time, and doesn't require vinegar, which can sometimes make your eggs, well, vinegar...y.
This is egg poaching related, but I just remembered this. The absolute best way to poach eggs, is not the technique (this is still very important), but using the freshest possible eggs you can. They have the tightest egg whites and the best flavor.