Why Freezing and Reheating Leftovers More Than Once Makes Them Taste Unpleasant
Freezing food for later consumption is a good way to boost your food bill, but for the tastiest, safest leftovers, you only need to freeze and thaw cooked food once.
According to Bon Appetit (which has a bunch of great tips for freezing and thawing safely at the link below), the reason is twofold. In terms of taste, repeated freezing and thawing can turn your food into mush. Due to the nature of dihydrogen monoxide, which is one strange molecule, water actually expands when it freezes, which can rupture the cell walls of your meat and vegetables, making them unattractively soft.
From a food safety point of view, new bacteria are introduced into the mixture each time it is thawed. While freezing can stop the growth of bacteria, it will not necessarily kill all types of introduced pathogens, so it is best to limit the amount of thawing. (To be honest, my biggest concern is taste and texture; bland food is extremely unappealing.)
How many times can you truly defrost and re-freeze food? | Bon appetit