Why is the production of Baker's rosin seasonal?

We make our family rosins from the fresh liquid sap of living trees. During the colder temperature of winter, our trees go into sort of a hibernation mode which results in larger particles suspended within the raw colophony.

Unfortunately, large particle colophony results in rosin which is both noisy and dusty, so we don't even bother with it. Instead we end production until things warm up again.