How to Moisten Dry Tobacco
By Per Georg Jensen - Mac Baren Tobacco

  1. Open the tin or pouch and place it in a plastic bag.
  2. Bring a kettle of water to the boil.
  3. When steam starts to form, hold the opening of the plastic bag over the steam. Make sure that the steam goes inside the bag. 5 seconds of steam into the pouch will be enough.
  4. Knot the bag closed and allow to stand for about one hour.
  5. The tobacco in the bag will absorb the moisture.
  6. After about one hour the tobacco will have regained its original moisture level.
 
Sources:
The above information has been gathered from a variety of sources including but not limited to the following:

Mac Baren Tobacco
,
Articles by William Serad
e-articles by G.L.Pease
Craig Tarler, William Ashton Taylor, Charlie Price
YouTube
and assorted other arcane sources