An aroma-compound, also known as an odorant, aroma, fragrance, or flavor, is a chemical compound that has a smell or odor. A chemical-compound has a smell or odor when it is sufficiently volatile to be transported to the olfactory system in the upper-part of the nose.

Generally molecules meeting this specification have molecular weights of <300. Flavors affect both the sense of taste and smell, whereas fragrances affect only smell. Flavors tend to be naturally occurring, and fragrances tend to be synthetic.

Aroma-compounds can be found in food, wine, spices, perfumes, fragrance oils, and essential oils. For example, many form biochemically during the ripening of fruits and other crops. In wines, most form as byproducts of fermentation. Also, many of the aroma-compounds play a significant role in the production of flavorants, which are used in the food-service industry to flavor, improve, and generally increase the appeal of their products.

An odorizer may add an odorant to a dangerous-odorless substance, like propane, natural gas, or hydrogen, as a warning.

It is through the aromas of wine that wine is tasted. The human tongue is limited to the primary tastes perceived by taste receptors on the tongue-acidity, bitterness, saltiness, sweetness and savoriness. The wide array of fruit, earthy, floral, herbal, mineral and woodsy flavor perceived in wine are derived from aroma notes interpreted by the olfactory bulb. In wine tasting, wine is often smelled before being drunk in order to identify some components of the wine that may be present. Different terms are used to describe what is being smelled. The most basic term is aroma which generally refers to a "pleasant" smell as opposed to odor which refers to an unpleasant smell or possible wine fault. The term aroma may be further distinguished from bouquet which generally refers to the smells that arise from the chemical reactions of fermentation and aging of the wine.

Aroma vs. bouquet

In professional wine tasting, there is generally a distinction made between "aromas" and a wine's "bouquet" while in casual wine tasting these two terms are used interchangeably. An aroma refers to the smells unique to the grape variety and are most readily demonstrated in a varietal wine—such as lychees with Gewürztraminer or black currant with Cabernet Sauvignon. These are smells that are commonly associated with a young wine. As a wine ages, chemical reactions among acids, sugars, alcohols and phenolic compounds create new smells that are known as a wine's bouquet. These can include honey in an aged Sauternes or truffles in a Pinot noir. The term bouquet can also be expanded to include the smells derived from fermentation and exposure to oak. In Burgundy, the aromas of wines are sub-divided into three categories-primary, secondary and tertiary aromas. Primary aromas are those specific to the grape variety itself. Secondary aromas are those derived from fermentation and oak aging. Tertiary aromas are those that develop through bottled aging.