Well, wood, being a cellulose fiber coming from plants (briar included), there's an amount of sugar that is present. Each species of plant has its own thing going on, and for that matter, even two identical plants aren't really identical, being forged by season, water, conditions, soil nutrients...
...I wonder if the better-tasting briar simply had a better time with life (kind of anthropomorphic, I know :no: ) and lends that to our tongues. Or it's masochistic in nature and the sweet stuff was thriving on drought, bugs, toads falling from the sky and insults hurled in its general direction.
My first experience with this was a cheaper Tsuge Kaga a brother wasn't into and gave to me, and the other was a Peterson my extended family bought for me. Both times, bowl coating went bye-bye, and it was epic pipa brûlée .