Chianti Classico wine festival - every year on second weekend of September and the preceding Thursday and Friday, 6 - 9 Sept 2012. On Thursday, the festival starts at about 5 pm, and on Friday, Saturday and Sunday at about 11 am and the stands close at about 8 pm. The idea is that you buy a wine glass from the Segretaria (price in 2011 was 10 euros) along with a ticket that allows you to taste up to eight of the wines offered at the stands. I have heard but not seen that they can run out of glasses.
Thursday 6th from 5 pm to 9 pm
Friday 7th from 11am to 9 pm
Saturday 8th from 11am to 7pm
Sunday 9th from 11am to 9 pm