Talk to Maven at the Bee and Barb then head to Whiterun to talk to Mallus Maccius at the Bannered Mare. Go to Honningbrew Meadery and speak to Sabjorn. Poison the nest of vermin in the basement but watch out for the crazy man living down there. Head to the brewing-house and poison the brewing vat. After, return to Sabjorn to receive payment for getting rid of the pests then attend the tasting. Talk to Mallus Maccius and then return to Riften to talk to Maven.