Big bluestem is a perennial, warm-season grass that produces spikelets with appendages and awns. This chaffy grass species does not readily flow through commonly available field sowing equipment. In addition, spikelets may not be filled resulting in decreased pure live seed (PLS). Intact caryopses can be extracted from spikelets with seed conditioning equipment; however, mechanical damage may occur. The objective of this study was to determine the optimum water activity (aw) needed to minimise mechanical damage during conditioning and thus achieve high seed quality. Water activity (aw) of big bluestem spikelets was adjusted to 0.55, 0.65, 0.75 or 0.85. The spikelets were then brushed with a brushing machine (Westrup LA-H) for 1, 2 or 3 minutes. Greatest germination was obtained with caryopses extracted from spikelets adjusted to 0.75 aw and brushed for one minute. Brushing spikelets with lower water activity or for longer durations resulted in greater mechanical damage to the caryopses. Recovery of caryopses from spikelets was less than 50% in all treatments. Caryopses and spikelets showed similar ageing trends thus brushing did not reduce longevity. Methods are presented to increase seed water activity to a desired level prior to brushing.