Why does my PLA filament keep snapping? Why does my 3&nbsp;mm PLA filament always snap near the spool some time (usually a few hours) after a print has finished?

I have had it snap mid print but this is quite rare.

I have 3 rolls of 3&nbsp;mm PLA filament from Velleman and 3DPrima. They all exhibit this behavior. They are between 2 and 3 years old. Each roll is stored in a foil bag with some desiccant, although this was not the case in the first year. The temperature in the room ranges between 14&nbsp;°C and 18&nbsp;°C in winter and rarely up to 30&nbsp;°C in summer. Current relative humidity is 49&nbsp;%. In summer I think I have seen it as high as 70&nbsp;%. I baked one spool in the oven at about 50&nbsp;°C for a few hours but this does not seam to have helped. When I remove the loose end of filament from the extruder after it has broken, some length of it seams to snap easily and some of it will just bend.

The printer has a direct extruder so there is no bowden tube.
PLA seems to become brittle with age. Micro-fractures develop on the surface, and they will grow if filament is taken off the spool and held straight. This behaviour does not seem to be linked to moisture content. The best course of action is probably to use PLA quickly. Don't give it time to age.