bitter

Bitter is one of the five basic tastes detected by the gustatory system. It is often described as sharp, pungent, or harsh, and it commonly signals the presence of potentially toxic or unpalatable compounds in nature. The perception of bitterness varies among individuals and can influence food choices and dietary habits.

Biology and chemistry: Bitter taste receptors, known as T2Rs, are G-protein–coupled receptors located on taste receptor cells within taste buds. Humans possess many functional T2R genes, enabling detection of a wide range of bitter compounds. When a bitter compound binds to a T2R, a signaling cascade is triggered that sends a taste signal to the brain. Bitter substances are chemically diverse and frequently include alkaloids, glycosides, and terpenoids, many of which plants use as defenses against herbivores.

Sources and examples: Bitter flavors are prominent in coffee, dark chocolate, certain leafy greens (such as kale and arugula), grapefruit, and hops in beer. Quinine in tonic water is a well-known source of bitterness, as are bitter liqueurs and bittering agents used in foods and beverages. Bitter compounds are also found in some medicines and supplements, which can influence palatability and compliance.

Variation and implications: Genetic differences influence bitterness sensitivity. Some people are highly sensitive to bitter compounds (supertasters), while others perceive them less intensely. This variation can affect dietary preferences and nutrient intake. Bitter taste receptors are also present outside the tongue, including in the gut and airways, where they may play roles in digestion and immune responses.

In culture and industry, bitterness is balanced with sweetness or texture to create desirable flavors, with bitterness measured in contexts such as brewing bitterness (IBU) or culinary balance.