Zinfandel wines leave their mark on you. As I strolled out of Fort Mason's Hearst Pavilion Saturday earlier this month, I looked down and noticed my fingers were stained purple. I had tasted more than 30 wines over the course of two hours at the 18th annual Grand Zinfandel Tasting thrown by ZAP, Zinfandel Advocates and Producers. The next day, my index finger still bore the mark of Zinfandel. People love this grape because it possesses that kind of indelible power, joyfully married to flavors of raspberry, chocolate, and spice.