This paper proposes a system to enhance the degree of subjective deliciousness of food visually perceived by a person by automatically changing its appearance in a real environment. The system is called the Food Appearance Optimizer. The proposed system analyzes the appearance of food in a camera image and projects an appropriate image onto the food using a projector. The relationship between the degree of subjective deliciousness and four simple appearance features for each food category is modeled using data gathered via a crowdsourcing-based questionnaire. Using this model, the system generates the appropriate projection image to increase the deliciousness of the food.