system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: what is the difference between fresh and frozen food from a chemistry perspective?
gpt
First thing is if you freeze food improperly, water will freeze inside the cells in such a way that crystals of ice will form, piercing through the cell walls and degrading the quality of the food.

Second: a lot of processes require certain molecules to be dissolved in liquid water. When you prevent that from happening, those processes stop. For example, when fruits ripe, the cell walls start disolving in liquid water (e.g. pectin from the walls gets degraded by the enzyme polygalacturonase and becomes soluble).

For most chemical reactions, the rate of reactions increases as the temperature increases. If you lower temperatures, most processes will start having negligible reaction rates, that's why your fridge preserves your food (by slowing down everything, including bacterial growth).

If you freeze, anything that relies on liquid water is basically put to a stop. Imagine being in a pool and trying to reach the other side of the pool, and then all the water around you freezes and you basically can't move anymore, you just have to sit there and wait. Same thing happens to molecules dissolved in the food's water.


tl;dr liquid water allows molecules to interact and come in contact. Freezing water removes that possibility.