You dont need a vacuum bag it can be done without of course.Are you using a vacuum bag? It has to be vacuumed so that mold will not grow. A few folks have had luck without vacuuming, but they are probably starting with the herb a bit dryer and are wrapping it up very tight.
I just find I have a far greater control over the fermenting and can get vastly different results and levels of cure using them.
I did this for years without one so I know it can be done.
I just prefer the knowledge that it will not mold and can be manipulated in ways that are not possible without one.
I spent the whole day yesterday sorting out the buds and preparing lots of experiments.
I should have some good cures in a few months time.
Heres a few 9 week Mulanje buds from yesterday the smell is amazing I just love it so far the fermented smell is now coming out its mind blowing already on some of my earlier cobs.