How does a sealed container preserve food safely at room temperature for months/years, but a sealed contained of leftovers in the fridge spoils in less than a week?

Question

For dinner today, I had a liquid precooked curry mix (sauce, cooked veggies etc..) that comes in a little foil pouch and doesn’t have to be refrigerated- just heat the pouch in hot water for 5 minutes and pour over cooked rice. All the food is precooked, just chilling at room temperature in that pouch for months, but perfectly safe to eat.

How can it be so safe and not-spoiled like that, when the same ingredients sitting in a Tupperware in the fridge will go bad in just a few days?

In: Chemistry

Answer 1

It depends, but the main factor is sterility. For something to spoil dangerously or just unpleasantly, it has to have growth of bacteria or fungi (viruses don’t really apply here), which eat the food you want to eat.

One way to avoid that is to process and package everything as clean as possible. The less contamination you start out with, the less likely it is to spoil. You can also package the food in vacuum sealed containers, as a lot of pathogens need oxygen to survive. Similarly, you can package food with a different gas to displace all the oxygen (meat is packaged with CO2). Then the final option is to sterilize the food, usually with radiation, to kill all the organisms living in it. This sterilization can be performed with the food already sealed in it’s packaging, so nothing new can be introduced.