Tobacco like any natural product has a shelf life, whilst this shelf life can last quite a long time the tobacco starts to dry out the moment you break the seal. In an unopened pack the tobacco should stay fresh for around two years - however we know you've bought it to smoke so that's not really a consideration.
You may not realise it but the actual tobacco production process is designed to dry out the leaves, this process allows for chemical changes to take place in the leaves allowing for a smoother less harsh smoking experience. However the producers are careful not to let the produce dry out completely, to halt the process they seal the smoking tobacco in an airtight package just at the right moment.
How tobacco stops being fresh
As soon as you open the pouch the drying process starts again, everyone smokes a pouch at a different rate so whilst some will consume the pack in a matter of days it might take others a week or two to finish it off. No matter how quickly you smoke we'd recommend working to keep your tobacco in the best possible state - after all you've paid a lot of money for this smoke so you should get to enjoy it in peak condition.
Methods to stop tobacco drying out
Whilst you can't stop the drying out process you can introduce moisture to keep the tobacco fresh. Some methods suggest using a fine mist sprayer to squirt a little water directly onto the tobacco, however this can firstly overly dampen the tobacco and change the flavour profile. This also might result in you having to re-dehydrate your tobacco so it's not an ideal solution.
The industry standard recommendation is to use a hydro-stone to introduce moisture into the atmosphere of where you store your tobacco. These are simple, cheap and readily available terracotta stones. By soaking them in a bowl of water they absorb the liquid and as they dry out they will gradually release it into the air. Therefore when stored in a pouch of tobacco the hydro-stone won't make the tobacco wet but will keep it moist by increasing the water content in the air. Bull Brand stock the Mascotte Hydro-stone and at £1 it is a cheap and simple solution to avoiding crumbly tobacco!