question:  How often do Bachus vines mature and what is the significance of that timeline?
context: "The Bogans have launched no less than four military campaigns in the last two decades. "Breaking and entering," Retief said. "Our function is merely to bring them together. The wine crop is just about ready. Now I don't know if you're familiar with the Bacchus vines we grow...?" "Only mature every twelve years. In between, the vines don't need a lot of attention, so our time's mostly our own. We've got long seasons back home. Our year's about eighteen Terry months. Blue-black sky, stars visible all day. Lots of skiing, bob-sledding, ice skating; and it's the season for woodworkers. That's the music-writing season. Autumn's our harvest season. Fruit, grain, that kind of thing; getting it in doesn't take long. This is Wine Year." "Our wine crop is our big money crop," he said. But this year...." Course, I'm only twenty-eight; I can't remember but two other harvests. Picking Bacchus grapes isn't a job you can turn over to machinery—and anyway we wouldn't if we could. Miles and miles of vineyards covering the mountain sides, and crowding the river banks, with gardens here and there. Big vines, eight feet high, loaded with fruit, and deep grass growing between. There's prizes for the biggest day's output, bets on who can fill the most baskets in an hour.... The sun's high and bright, and it's just cool enough to give you plenty of energy. Come nightfall, the tables are set up in the garden plots, and the feast is laid on: roast turkeys, beef, hams, all kinds of fowl. Fresh-baked bread ... and wine, plenty of wine. The cooking's done by a different crew each night in each garden, and there's prizes for the best crews. Matter of fact, pretty near half our young-uns are born after a vintage.
output:  Every 12 years a vintage is held, which also serves as a cultural festival that encourage young people to procreate.
options:  Every 18 years a vintage is held, which is a kind of celebration of art.  Every 12 years a vintage is held, which also serves as a cultural festival that encourage young people to procreate.  Every 18 years a vintage is held, which serves as a kind of celebration of life for both young and old people.  Every 12 years a vintage is held, wherein the young people are made to harvest all the grapes.