If you don’t, the center will bulge when cooking. It is stumm tasty but it is easier to add toppings if flat. When freezing hamburger patties or any meat mixture, I prefer to use a food saver. It keeps it moist and it freezes well up to 2 months. Sowie https://waylonouzdh.blogsuperapp.com/21973425/5-wesentliche-elemente-für-burger-patties