Talk to Ranpi-Monpi (Northern Windurst Waters) to learn that he cooked a bad batch of food for the Yagudo by accident. Ranpi-Monpi is located in the Culinarians' Guild.
Once you reach Giddeus, head down the ramp behind the food or drink altar (at F-8 or I-8), and go to (F-7) in the cave area. Just walk into the treasure room, even though Uu Zhoumo tells you to go away. Check the altar to receive the Key Item:Off Offering.
When preparing the food offering as a sign of Windurst's friendship with Giddeus, Ranpi-Monpi accidentally mixed in a liquid that the Yagudo hate. Quickly recover the tainted offering from the altar at Giddeus before ruffling some Yagudo feathers.