Another fun, inventive take on the traditional Brazilian caipirinha. The açaí gives it a good depth of flavour. I used the frozen açaí pulp, defrosted. I also make just caipirinhas with just red grapes and it's delicious too.
Put the slices grapes on the bottom of a 250ml glass, add the sugar and muddle it well. Add ice until the top of the glass and then add the cachaça and the açaí juice. Stir well (or shake it in a cocktail shaker). Serve!