Fuente: WIPO "tomato" An object of the present invention is to improve the richness of a wide range of foods and drinks, including plant-based foods. Provided is a taste improving agent containing olive oil so as to be 1 to 15 parts by mass with respect to 1 part by mass of a brewing by-product. The brewing by-product is preferably a brewing by-product of alcoholic drinks. The olive oil is preferably unrefined olive oil. The content of an unsaponifiable matter is preferably 0.2 to 3.5% by mass. The taste improving agent preferably contains a plant milk. Provided is a food or drink containing olive oil so as to be 1 to 15 parts by mass with respect to 1 part by mass of a brewing by-product. The food or drink is preferably a plant-based food. Provided is a method for improving flavor of a food or drink, the method including a step of including a brewing by-product and olive oil in a food or drink.