Anybody who wanted to get a cocktail education in this town used to be able to hang around Louis 649 every Tuesday night for a boozy tasting accompanied by a spirited lecture. We learned a lot about gin on one occasion and got to know PDT honcho Jim Meehan’s cocktail-menu obsessiveness on another. The tastings dried up at some point, but now Grub hears the happy news that they’re coming back. Next week’s event features Purity Vodka, and the week after that spotlights cocktail-making at home. Tuesday-night tastings start at 8 p.m., and it’s best to arrive early — any kind of free education these days is bound to be competitive.