Sometimes, not all grains are individually sealed, allowing them react with atmospheric moisture. Certain propellants, like White Lightning, are more likely to exhibit this issue than others. The impact on performance is negligible, but it can adversely affect ignition. If you have different grains, put the good looking ones at the forward end of the motor, where the igniter is positioned and you won't have any problems. Should you encounter a motor where all grains are affected - for example one that was unpacked, but not flown for some reason - carefully clean them (especially parts that touch the igniter) with sand paper or similar means.
Reinhard
