TART-TASTING is a term used to describe food or drink that has a sharp, acidic flavor. The crossword solutions for this term are SOUR (4 letters), BITTER (6 letters), and ACERB (5 letters). SOUR is a taste sensation that is caused by acids, such as citric acid found in lemons. BITTER is a taste sensation that is caused by alkaloids, such as caffeine found in coffee. ACERB is a taste sensation that is caused by tannins, such as those found in red wine. All three of these tastes can be described as tart-tasting.