Open dating food
However, shelf life alone is not an accurate indicator of how long the food can safely be stored.
For example, pasteurized milk can remain fresh for five days after its sell-by date if it is refrigerated properly.
In the case of bacteria and fungi, the reactions needed to feed and reproduce speed up at higher temperatures, up to the point that the proteins and other compounds in their cells themselves begin to break down, or denature, so quickly that they cannot be replaced.
Bacterial contaminants are ubiquitous, and foods left unused too long will often be contaminated by substantial amounts of bacterial colonies and become dangerous to eat, leading to food poisoning.
The same is true, up to a point, of the chemical reactions of living things.
They are usually catalyzed by enzymes which change reaction rates, but with no variation in catalytic action, the rule of thumb is still mostly applicable.
The usually quoted rule of thumb is that chemical reactions double their rate for each temperature increase of 10 °C (18 °F) because activation energy barriers are more easily surmounted at higher temperatures.
However, as with many rules of thumb, there are many caveats and exceptions.