On many occasions now, both at home and elsewhere, I have noticed that kosher hamburgers often turn egg-shaped (as opposed to round) once they are cooked. Having cooked non-kosher hamburger before, I am convinced that this is only in kosher burgers. Two brands in particular are Teva and ShopRite. Also, at the kosher cafeteria in my school, there has been the same phenomenon. The pre-made patties are perfectly circular before I cook them. Does this happen to you? Why?