What lends certain wines that "peppery" taste?

[vindespoir]

Does anyone know what specifically about the grapes or the processing, aging etc creates the taste as well as the scent which - to me - is like black pepper? I've noticed it before, but recently I tasted a merlot at a local vineyard and the pepper was WAY forward, the strongest I had ever tasted and it got me to wondering. The lady behind the bar didn't know.

Great board, I've been lurking for a while...