With real beef burgers, it is actually the saturated fat which is causing the meat to stick together and form a burger. Saturated fat molecules stack together firmly and are solid even at high temperatures. So, the sticky fats in real beef do a good job of holding the burger together. The saturated fats only start to liquefy when they are on the grill. When this happens, the fatty liquid acts like a glue to hold all of the ingredients together.
By comparison, vegetables and veggie crumbles don’t have much fat at all (hooray!). They especially don’t have much/any saturated fats. While this is a major plus for your arteries, it doesn’t help when you are trying to make the perfect veggie burger. The few unsaturated fats which are in vegetables aren’t very sticky. They tend to be liquid at room temperature, which means that they aren’t going to do a good job of keeping your burger together.
HOW TO GET YOUR VEGGIE BURGER TO STICK TOGETHER
It IS possible to make a dense, satisfying veggie burger which doesn’t fall apart. Here are a few ways you can do it.
2. Use an Egg Alternative
Agar Agar: This is my personal favorite binder for all sorts of vegan recipes. Agar agar is a powder made from a sea vegetable. It is known as vegan gelatin because, when mixed with water, it becomes gelatinous. Mix the agar agar with equal amounts of water before adding it to the veggie burger mix (or as the recipe directs). You can buy agar agar at most health food stores and at Asian food stores.
Arrowroot, Cornstarch, Cornmeal, or Tapioca: All of these are common binders used in cooking. You will need to mix them with a bit of warm water before adding them to your veggie burger mix.
Wheat Germ: Wheat germ is a decent binder and also adds some fiber and crucial nutrients to your veggie burger. The downside is that it does have a gritty taste. Like with the other binders, it helps to mix it with a bit of water before adding it to the mix.
Flax Meal: You can make a “flegg” (flax egg) by mixing 1 TBS flax meal with 3 TBS water. It is a great binder and works as an egg substitute in just about any recipe.
3. Add a Starch
VEGGIE BURGER TIPS:
Make sure the grill or pan is VERY hot before you put the Beyond Meat Beefless burger down. That way, the fats, binders, and starches in the veggie burger will start congealing together immediately and the ingredients won’t have time to separate.
Add some extra oil to the pan or grill. Or, alternatively, coat the outside of the burgers with some oil before putting them down. This will ensure the veggie burger doesn’t stick to the surface."
See explanations @ Beyond Meat