I have been trying to understand fermentation of cannabis and there apparently is some bacteria that is responsible. Most forums that discuss this mention anaerobic bacteria (living without air) which would then suggest that this is the process that happens in the masonry jars after you stop burping and perhaps why people report changes in color and taste when curing longer periods of time. The guys looking for more hard core fermentation processes compress their buds, either inside a corn husk/leaf that they tie up with strings or in bamboo pipes and then subject to heat, either by burying them in warm sand, earth or just place in a warm area (about 30 degrees celsius).