its best to mill it just prior to use or the inevitable loss of volatile oils as explained here
Cold-pressed flaxseed oil is an excellent source of dietary ?-linolenic acid (ALA). However, breakdown of ALA in the oil, either in the seed before or during storage, or as a result of processing, may result in unacceptable flavors. Screw-pressed flaxseed oil from four seed lots and a commercial sample were analyzed for headspace volatiles (HV) by solid-phase microextraction; for nutty, painty, and bitter flavors; and for overall quality. HV and sensory analyses were performed after storage for 7 d at room temperature and again after 15 wk at 4C. Marked, significant differences were observed between samples for painty and bitter flavors and overall quality, but only slight differences for nutty flavor (P<0.05). Samples remained stable between the two storage periods. HV traces showed distinct differences between samples in number of peaks and in peak heights. Areas under peaks corresponding to select retention times were positively correlated (P<0.01) with nutty, painty, and bitter flavors. Therefore, the HV analysis by solid-phase microextraction may be a useful tool for screening flaxseed lots to be used for the production of screw-pressed oil.
An often overlooked source of flaxseed is from pet shops [bird seed]