Most rifle powders are single-based and use nitrocellulose as the energetic component. Some pistol powders are double-based and add nitroglycerine to that. In their pure form, both chemical compounds will easily detonate (reaction front progresses at supersonic speed), which is bad in firearms.
The art of powder making is to add retardants to the energetic compounds and shape the grain so that a less violent deflagration (reaction progresses at subsonic speeds) occurs. There are also stabilizers added to delay the natural decomposition of the nitro-compounds over time.
If the manufacturing process fails to remove all acid traces from the nitration of the raw ingredients or adds too little of the stabilizers, the powder will become more brisant (faster, more shattering) within the expected shelf life. If a tried and trusted powder suddenly acts erratic and spiky it is time to discard that lot.
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