A perfumer is an expert on creating perfume compositions, sometimes referred to affectionately as a nose due to their fine sense of smell and skill in producing olfactory compositions. The perfumer is effectively an artist who is trained in depth on the concepts of fragrance aesthetics and who is capable of conveying abstract concepts and moods with compositions. At the most rudimentary level, a perfumer must have a keen knowledge of a large variety of fragrance ingredients and their smells, and be able to distinguish each one alone or in combination with others. They must also know how each reveals itself over time. The job of the perfumer is very similar to that of flavourists, who compose smells and flavourants for commercial food products.