These fudgy squares of chocolatey bliss are infused with the unexpected tang and depth of flavor from beer malt vinegar. Yes, you read it right—beer malt vinegar! I used American Vinegar Works Beer Malt Vinegar which provides a more intense chocolate zing and balance to the sweetness of the brownies. The addition of vinegar adds a unique flavor that perfectly complements the intense chocolatey goodness. American Vinegar Works, is a small group of craft vinegar makers in New England. Their delicious small batch vinegars are slowly fermented, barrel aged and bottled by hand. I have a few of their vinegars and love using them.