Food preservation
All the techniques that slow food spoilage by acting on micro-organisms and chemical reactions, with varying effects on nutritional value.
Preservation targets two distinct kinds of deterioration: microbiological spoilage, which is a food safety issue, and chemical spoilage (oxidation, rancidity, loss of vitamins), which affects quality without necessarily making the food dangerous. The two do not progress at the same pace.
The techniques work through a small number of levers: temperature (refrigeration, freezing, pasteurisation, sterilisation), available water (drying, freeze-drying, salting, sugaring), acidity (fermentation, vinegar), oxygen (vacuum packing, modified atmosphere) and preservatives.
Frozen food is often richer in nutrients than « fresh » produce. This is surprising, but it makes sense: vegetables destined for freezing are picked at maturity and processed within hours, which locks in their vitamin content. A « fresh » product that has spent several days in transport and on a shelf has had time to lose some, especially vitamin C.
The two date labels should not be confused. The use-by date (« to be eaten by ») is a food safety matter and must be respected. The best-before date only signals a possible drop in quality: a product past it is generally still fine to eat, and this confusion drives a large share of household food waste.