How does one know if slightly crushed tetrapaks are safe to eat from? I have never heard of problems from them but wonder as they get a bit crushed from picking them up repeatedly. This article How to Know if Canned Food is Safe Past its Best Before Date says to avoid package if it is cracked, crimped or pinched but perhaps that applies to cans? Thanks!
Tetrapaks vs. canned food
packaging
Related Solutions
It sounds like by "temperature" you're referring to the setting of your stove. If your stove is powerful enough that you don't need it at its maximum power to keep water at a rapid boil, then you can of course reduce the setting once you've returned it to a rapid boil (between your steps 3 and 4). On the other hand, if you have a smaller, older stove, you might need to keep it at high to keep the water boiling rapidly. So the answer is "maybe" - you do whatever you need to do with your stove to keep it doing what the directions say (boiling).
That said, this isn't necessarily the best way to cook pasta. You should test it, rather than counting on the time on the package to be accurate. And you don't actually have to cook it at a full boil, or boil the water before adding the pasta; see this great column by Harold McGee on cooking pasta in a way contrary to popular wisdom, and a Food Lab article based on it. You can in fact start with pasta in just enough cold water, bring it to a good simmer, and keep it there until it's done.
The problem is that many 'food grade' tins are coated, and not solid. As such, cleaning them can end up flaking off the coating that's been applied, making them reactive.
Unless you're dealing with antique materials, I suspect that the majority of 'tins' are going to be either coated steel, or stainless steel.
Although I mentioned looking for tooling marks, and if it's matte or shiny, an easier test might be to use a magnet -- if the magnet sticks, they're most likely steel, and thus prone to rusting. Even if they're coated, if you put something moist in there, it can seep into any cracks it finds, leach at the metal, and then ruin your food. I had this happen with some Pecan Whiskey Cakes that I had put up, as they need to soak for a couple of months ... I now understand why my aunt wraps hers in (alcohol soaked) cloth, then a plastic bag, then whatever she's going to store it in.
You could probably do the same thing as you're only dealing with a few days -- wrap it in plastic, then put them in the tin.
It's possible that some (non-stainless) steel containers might have a more durable coating ... but unless it's specifically sold as being re-usable (or as wombar mentioned, for the industrial/institutional market), it's likely made to keep the costs down and not intended for re-use.
You should also avoid acidic or salty items, as they're known to pit stainless steels, especially when there's moisture and/or poor ventilation.
Best Answer
It depends on the damage to its layers.
This is the layout of a tetrapak container:
Now, obviously the container should not be considered safe if layers 1-3 are compromised. But small damage in layers 4-6 should not be considered invalidating.
Since the package is flexible, I don't think that slight crushing compromises any of the more important layers.