The Luau is an event in Stardew Valley that takes place on Summer 11 between 9 AM and 2 PM on the Beach. You can talk to Mayor Lewis to begin the soup tasting. At the end of the tasting, the time is changed to 10 PM and you are teleported to your farm.
During the Luau, you have the opportunity to place a food ingredient in the communal soup pot. The Governor will later taste the soup, and his reaction depends on the quality of the ingredient you added.
*However, this doesn't have any impact on the player as it is just a fun diversion.*
Adding nothing will result in the Governor saying it's missing someone's unique voice.
Adding Red Mushroom makes the governor sick and no one will eat from the soup.
Adding a poor quality ingredient makes the soup disgusting.
Adding an eggplant, golden parsnip, golden garlic, spice berry or a golden hot pepper results in "I don't have much to say... It's a very average soup." Mayor Lewis will agree, and even though the soup is average, the Luau is considered a success.
Adding a golden grape, standard strawberry, grape wine, or silver/golden spice berry results in the Governors comment to be "Ah... that's a very pleasant soup" and then says the valleys produce never disappoints. (Perhaps the normal response?)
Adding a golden red cabbage, truffle, golden mutant carp, golden Goats milk, or a golden Super Cucumber makes the soup taste out of this world