I pan fry my ground venison (that I trimmed all fat and most tendon and membrane) in a non stick pan with some salt and a little onion. After dehydration, it's superlight hard little granules that are a little smaller than grapenuts and coffee colored. I put some in the cold water before heating and let it hydrate during the heating process. Then I add the soup mix, noodles, or what ever you want to add and finish cooking. If you don't it tends to be little slightly tough burger bits.
I tried several times dehydrating a cooked hamburger patty, since I was craving the idea of having a hamburger in the field and was not successful.
Similarly I tried dehydrating spaghetti sauce (for obvious reasons since I was successful with the burger) but that didn't work either.
I bought a cabelas commercial food dehydrator last year and may explore low temp dehydration for possibly better results.
Mike