In an upright freezer. If you do it quickly it doesn't get freezer burn. Check out the book frost bite (there's also one for teens & kids) and it talks about snap freezing in a regular freezer. And hot it prevents the food from getting freezer burn as it can do in a bag. I have done it for less than 12 hours and it works fine too. She does it with all sorts of things from mini quiches, to cooked samosa's or even meatballs.