I love the magic mystery crystals!
Sometimes it seems they start forming pretty early on, depending on density and moisture I guess, here's some MB ODF from March 2012 I opened 3 months ago, the flakes had a nice light dusting with glitter:
...and dig this JKP that was only 6 months old from an old thread, this thing certainly looks like a majik brownie!
http://pipesmagazine.com/forums/topic/jack-knife-plug
Like it's been said, there is some debate to what this stuff actually is. Who knows? I'd love to see it get the full scientific treatment complete with chemical analysis & microscopic pix!
Here's some wisdom nuggets from G.L. Pease on the subject:
"The crystals that appear on aging tobacco are more likely something that is soluble within a narrow pH range.These crystals are not very soluble in water. As the tobacco ages, the pH changes, and some things that haad previously been in solution may, and apparently do, precipitate out. But, from some very preliminary testing, it is almost certainly not sugar."
&
"I don't think the crystals that form on tobacco are sugar. A long time ago, I did some messing around with some of the crystals I discovered in a tin of Va, a little analysis, and they did not behave like any sugar that would be in tobacco. They were not even soluble in water! At the time, I could neither harvest enough of them, nor did I have access to the necessary equipment to get a read on what they might be."