We jar our body butter when it's whipped, silky, and smooth. But, if your jar was left in the car on a hot day, it could have melted and developed a grainy texture. The good news is that it's perfectly safe to use and won’t affect the performance of the body butter.
The graininess (or butter bumps) are a result of different fatty acids cooling down at different temperatures. If you want to restore the wonderful whipped texture you can re-whip your body butter. This post explains how to restore your body butter to its silky smooth whipped state.