how come re-freezing food is bad?


If I thaw something in the fridge (so never in food danger temps) to only use some of it, why do food safety rules say I can’t re-freeze the rest?

In: 2

It’s likely still safe to eat as long as you aren’t hovering in the danger zone, but the flavor and texture will change from repeatedly refreezing food. A portion of cells that make up the food will expand and burst and there is moisture loss every time it freezes and the texture and flavor changes each time.

> If I thaw something in the fridge (so never in food danger temps) to only use some of it, why do food safety rules say I can’t re-freeze the rest?

They don’t; you can refreeze foods that have been thawed via refrigeration. It will probably be bad for the taste/texture if you do it too much, but it’s not a safety issue for the reasons you noted. It can be if you leave it in the refrigerator for too long, however; pathogen growth slows under 40F but doesn’t stop. If you decide to refreeze it, do so immediately, and keep in mind the total amount of time it has been at refrigerated temperatures (and further still keep in mind that some of the time it has spent in the freezer has been at refrigerated temperatures while it was freezing).

Depending on the food and depending on how it was thawed and stored, it could be a risk.

Safety rules err on the side of caution, because erring on the side of reckless would almost certainly result in more food borne illness.

There are several issues at play for food safety (not counting taste / quality).

1. Freezing / thawing takes several hours each way – it is not instant (this is key).

2. Bacteria reproduce *fast* under good (e.g.)
room temperature / danger zone) conditions. Some species can double in ten minutes in ideal situations. Being cold (not frozen) slows this reproduction down but doesn’t stop it.

3. Bacteria (assuming plenty of food) have an exponential growth rate ( I did say “double” earlier)

So let’s say (back of napkin math) that your food starts with 100 bacteria in the freezer. You start thawing the food, and it takes three hours to thaw, sits in your fridge for ten hours, and then you put it back in the freezer where it takes another three hours to refreeze. Let’s say that because of the cold the bacteria are only doubling every hour, and that nothing happens the first and last hour of freezing. That gives us 14 hours of doubling.

P(14) = 100*2^14 = 1,638,400 bacteria go to sleep in the freezer on your food when it is refrozen – and they have been eating and crapping on that food for 14 hours (for most bacteria, their waste is what makes us sick). This means when you take that same food out of the freezer for round two, you are starting with 1,638,400 bacteria instead of just 100. If you do the same thing again (thaw, leave in fridge, refreeze) you would have 26,843,545,600 wee beasties for your immune system to fight when you take it out for round #3.

This is why food spoils in the refrigerator also – it just spoils slower than at room temperature. This is why you shouldn’t eat leftovers after three or four days – the bacteria are quietly doubling in there – what types and how quickly (maybe the bacteria only doubles everything four hours due to cold, etc) can be very unpleasant to determine (food poisoning).