I was wondering if you could tell me why when baking fish or meats occasionally a white, thick skimmy matter forms.
- Thanks, Effie
I'm no expert, and I'll probably be corrected by a few foodie scientists out there, but this is what I was taught many years ago.
The white stuff usually comes out when something is cooked at too high a heat, is overcooked, or dries out. It's made up primarily of albumin, which is a type of water-soluble protein found in blood and egg whites (among other things) although albumen (which is actually the term for egg whites) mustn't be confused with albumin. Albumen are only around 50 per cent albumin. Writing this I'm getting giddy as I'm supposed to be answering culinary queries and now I'm becoming Dr Gordon. Oh well, it's all the rage to do molecular gastronomy ...
Because the protein is soluble, and the meat or fish (salmon especially) cooks, releasing moisture, as it seeps to the outside of the fillet it sets when it comes into contact with heat, as an egg white does. It's nothing to worry about, but it doesn't look particularly appetising. It is best to wipe it off with a sharp knife just before you serve your meal.
When making fish or meat stock, a similar thing occurs. The fats and proteins are forced out of the bones as they heat up and float to the surface where they can sometimes look like a toxic foam. That's why you're told to skim a stock as it simmers away on the stove. What I have found though is that if you cook fish bones long enough the stock, without skimming, pretty much clears itself. This is interesting, because another part of the fish, the bladder (when turned into isinglass) is sometimes used to clarify white wines. Bet you didn't know that. Egg whites are also often used (not surprisingly then), as are gelatine and casein - all of which, apart from the casein, contain collagen which binds with the particles in the grape juice, pulling it all together, thence making the wine crystal clear.
Whenever I make a veal stock, or any stock from large bones, I always cover them with cold water and bring to the boil and refresh three times before adding the vegetables and wine etc as they give off enormous amounts of 'foam' and you'll find yourself skimming away half the herbs and goodies as you continually skim all day long.
However, all this coagulation can work to our benefit when it comes to consomme, the clear broth beloved of old hotels and classic restaurants. I once had the most amazing truffle-flavoured game consomme that was served with shaved white truffle and thinly sliced pigeon breast floating in it which was completely divine. The broth is made and then a mixture of egg whites and minced lean meat (no fat please) or fish is whisked in and the broth brought slowly to a simmer. It cooks for a bit longer and is then left to cool a little. The proteins in the egg and meat have coagulated with any solids floating in the stock and you are left with a crystal clear consomme - simple gastronomic heaven!
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