[deleted]

Two problems -

1. Most of food consists of cells of some kind, either plant or animal. Freezing creates crystals that are like tiny knives that slice up the cells, with refreezing you'll progressively turn your food into unrecognizable mush.

2. Many microorganisms will start attacking the surface of our foods and growing the moment they can, by the time the food is thawed they might have the beginnings of a rocking colony. It's not a huge problem if you just cook it and eat it right then, but if you re-freeze it and then rethaw it they can start again with their bigger colony, increasing the chances of getting you sick.

Very interesting . So because of all those sliced cells, microorganisms growth faster on thawed food ? Does it means that thawed food has to be cooked right away and can’t go to the fridge like fresh food ?

You actually can refreeze food. There may be some quality loss depending on what it is and how it was packaged.

If it was left at unsafe temperatures for long enough that would make it unsafe to eat, but if that happened it doesn't matter if you refreeze it not, apart from the extra time for it to defrost again.

Aren't micro organisms also made from cells? Wouldn't they also be destroyed during the freezing process?

Yeah, some will. However the cold may only cause a biostatistic condition(no/little growth). The food item (let's say steak) is dead and has no way to repair damaged tissue. On top of that, cows regulate their body temperature and don't need survive winters with their individual cells at or below freezing temperatures. Bacteria and other microorganisms do. So they can regulate the amount of water in their cell(s) and have other safe guards to rupturing at freezing Temps. Let's say.... fish are safe to eat raw if they have been frozen at a very low temp for a certain amount of time. Standard home freezers normally can't reach those Temps.

TLDR: little guys are built different

So are pine needles, which survive freezing temperatures without thermo regulation.

They do it by, in part, having less water content. Less water means less ice which means less or no cell rupturing from ice shards

These are two different problems.

The breakdown of cells from freeze-thaw cycles makes the food less appetizing.

The time spent in the "danger zone" (40-140F, or 4-60C) allows bacteria to grow, with bacteria growing faster at warmer temperatures. If you thaw food in the fridge, it should be safe for a few more days. If you thaw food on the countertop (and let it come to room temperature) and then put it into the fridge, it might go bad in a day.

So what if I thawed out a block of cheese but never opened it and threw it back the freezer?

The danger zone thing is where it kinda gets lost though. For example:

My parents get half a cow each year. Someone mixed some stuff up and put a chunk of the burgers in the fridge instead of the freezer. Well, the fridge was still below 40F (basement fridge is set pretty low) so the meat thawed but didn't hit the danger zone.

The rest of the family still living there were put off by it, so unless he cooked it without them seeing they didn't want it. So he gave me the thawed + refrozen ones. They're just fine.

Since it's just me and my wife, it's hard to get through 8 burgers fast enough. We just don't eat beef like that. Normally when we got a few packs they weren't thawed so we could just break the package in half due to the way it was packaged and thaw that half. If I was sure I could even break that in half and only take out the two we wanted to eat.

Well since these thawed I can't do that at all. They kinda squished together. So a few times now I put them in the fridge until they're thawed enough to break apart (or nearly completely thawed if doing it overnight) and then repacking them in batches of 2 to refreeze.

Two thaws, two refreezes, doesn't matter. Sure they might spoil a little faster if I leave them in the fridge now.... But it doesn't really matter.