How Brightness Works

The tongue is covered with specific taste receptors that detect acids in food, even at very low concentrations. When you take a sip of lemonade, the hydrogen ions [H+] in the lemon juice (citric acid and ascorbic acid) interact with the acid taste receptors and relay a signal to the brain, telling us that what we’re tasting is sour. Almost all the acids we eat are organic and contain the carboxylic acid group.

Humans can detect the aroma of some acids (acetic and butyric, for example), and we use this skill often as we decide what to eat. Tear open a bag of salt-and-vinegar (acetic acid) potato chips, and the unmistakably sharp odor of vinegar will punch you in the nose as that vinegar smell hits the odor receptors lining the inside of your nose. You immediately anticipate the delicious taste of the sour-salty chips.