A science guy told me that there is no one living that can describe what happens inside a jar, fermentation, that is.
What we do know, and what I know of that, is:
1. fermentation/aging occurs because tobacco is an organic substance, and from the time the leaf is pulled from the stalk, it starts deteriorating. Curing refers to "fixing" or slowing that deterioration down to a crawl, I guess. Removing most of the moisture allows tobacco to be stored in bales until the blender is ready to use it, more or less stopping all aging. If you watch the MB video on the front page they say this, referring to the many bales they have in house.
2. Thus some moisture is needed to restart aging, and thus whatever moisture is in it in the tin is necessary, as is water inside the jar.
3. The next important variable is air, not that it's presence or absence seems to affect the outcome. What it does affect is the type of fermentation that occurs, as it is known that it differs; the terms are, of course, aerobic and anaerobic aging. If there is air inside the container it ferments aerobically, if not anaerobically. Most advocate leaving some air in the jar, but I'm not sure it matters, as it will pass from one to the other when the air is gone.
4. If I'm going to resist smoking tobacco during aging, then I want the wait to be worthwhile. Virginia ages best, because of the sugar content, and to my non-scientific mind this means that the sugar is used as the fuel for fermentation. But I would not age non-premium tobacco of any nature. Why be patient aging tobacco that was mediocre in any case? Even if it ages, it would seem to me that GIGO applies.
5. In general tobacco mutes and melds during aging. If you like only vivid flavor don't age and smoke $5 Nicaraguan cigars.
6. This is my principle only, though a big player in the industry seemed to concur.
If you close a jar, it stays closed until you have met whatever aging time you've selected. Some claim they are aging tobacco but permitting themselves to sample the contents periodically. One guy puts the tobacco in a plastic bag inside the jar so as to minimize contact with air while retrieving a bowl's worth. But as I purist I believe that this couldn't be more wrong. It offends me purist sensibility; my consternation is mine and only mine. But if we say that we are buying a tin of vintage tobacco that's 20 years old, we are certainly speaking of a tin that long ago exhausted whatever oxygen was in the container, and that has been aging anaerobically since that time. That is, we commonly refer to a container whose tobacco contents have not tasted any air over the years. To my mind what is the point of forcing the tobacco to upshift into aerobic fermentation, and then downshift into anaerobic, repeatedly? This is a needless chemical shift. The tobacco was doing just fine closed. It's aging as aging is done even according to standard definition as regards the vintage, tin, above. Why fool around with it? Most of all, aging takes time and patience. One is going to extra effort to make it occur. If a aging is occurring as it needs to, why make life difficult for the tobacco?
Just my thoughts.
7. I knowledgeable member on another forum claims that some VAs don't age well, the Europeans. I have no opinion on this, though I hope he's wrong as I've been aging a canister of Heinrich Curly since 2003.
8. So how much air you leave inside the container and how firmly you pack the tobacco in it as anyone's guess. You could pack looser to have all the contents more exposed to the air in the container or more firmly to allow the chemical process intensify by the adjacent leaf. I don't think anyone knows.