4. Gently agitate, massage, and shake the bags for about fifteen to twenty minutes
. In this amount of time the contents of the quart bag should start to turn into solid ice cream. It is important that you are mixing the contents of the inner bag, but you don’t want to be so aggressive that you burst the inner bag or cut it on the ice. Double-bagging should prevent this. If your hands get uncomfortably cold, use a towel or an old T-shirt to hold the bags as you massage them; the bags will be quite cold and might become slippery with accumulated condensation. Consider using gloves or massaging while holding onto the top seal if a towel or similar cloth is not available.
5. Remove the finished ice cream from the sandwich bag and serve