G. L. Pease":gms9w3yh said:
Even if they were 100% identical in every respect at the point they were manufactured, by the time you get your hands on them, a tinned blend will be different, however slightly, from its bulk equivalent. There are several reasons for this.
When the tins are manufactured, they are partially evacuated to create a tight fitting seal between the rubber gasket around the lid’s circumference and the top of the bottom part of the tin. The tobacco is also packed much more tightly into the tins. This effectively does something similar to pressing the leaf, creating greater contact between the strands of different tobacco types, and the depletion of available oxygen encourages a different type of "aging" process. The tobacco, once produced, spends quite a bit of time in those tins before it finally gets to you, just because of shipping and handling times, so a lot is happening inside those little flat Petri dishes.
The bulk blend, on the other hand, is just bagged and shipped. No evacuation, and the thin films of the bags, though relatively impermeable to water, are less proof against gas exchange, so the internal environment is not as stable as it is within the tins. After as little as a few weeks, the differences can be pronounced, and it’s certain that much more time than that passes before the tins or bags reach you after their manufacture.