I've been purchasing fresh ginger from the same source for awhile, and it typically looks the same, but I'm noticing that sometimes the ginger has significantly more heat than at other times. I'm wondering if it has to do with the time of year it is harvested? How fresh it is (although the rizomes always appear equally plump)? Or something else? Any wisdom you can offer is helpful -- I'm just trying to have as consistent a final product result as possible.