My wife is having pregnancy cravings for (homemade) hamburgers, but has developed a prenatal allergy / intolerance to egg.
What is a possible replacement for egg to stop a hamburger pattie from collapsing into mince during cooking?
Have you tried not adding egg? In my experiments, egg is needed when you add breadcrumbs, but if you just form some ground beef into a patty and fry it, it doesn't fall apart. Hm, let me clarify that. If you take a single blob of ground beef straight from the styrofoam and press it in a patty press, it doesn't fall apart. If you take two pieces and put them next to each other in the patty press, it does fall apart as you cook it. So when I need to add an extra bit, I add it on top. That works. So there is at least one way you can make a hamburger without adding egg. Now, if you wanted to mix spices into the beef, then you might have a problem. I'll admit that. Better than nothing, though.
I've never used anything other than beef, dry spices, and sometimes garlic to make my hamburgers. Truthfully, I much prefer the taste of a burger with no binders. We buy our beef by the half cow, and make plenty of burgers. Freezer -> defrost -> Mix beef with spices -> Form burgers while still cold (I make a round ball with the meat, them compress it) -> straight to grill. We've never had any issues.
I will also say, that my wife is much better at making evenly sized, well formed burgers, that hold together really well..
There are two things you need to do to make perfect hamburgers without egg or other binder.
First knead the meat balls so that the meat binds together. Kneading give you a better bind you will get. Press the meat firmly into your mould before popping out.
Second, after forming into shape, refrigerate the meat pats.
This process first stretches the proteins in the meat. When chilled, the proteins contract again but now they are twisted together in a bond. When cooking, the pat will hold together just a well as any that you buy in a shop.
If find that this works even when I add liquids to the meat. I often season my meat with Worcester sauce mixed in. Even with this extra liquid the meat will hold together just fine. No egg required.
You can use what is called a flax egg, it is 1:3::milled flax seed: water (4Tbsp is about 1 egg in terms of binding strength). Not only is flax the secret glue in many vegan recipes, but it might be a good additive for your wife's diet.
Time for some molecular gastronomy. Transglutaminase ("meat glue") should work perfectly. http://en.wikipedia.org/wiki/Transglutaminase