People with a version of a gene that increases sensitivity to the bitter flavor of caffeine tend to be coffee drinkers, researchers report online November 15 in Scientific Reports. Tea drinkers tended to be less sensitive to caffeine’s bitter taste, but have versions of genes that increase sensitivity to the bitterness of other chemicals, the researchers found. In the new study, researchers examined DNA variants of genes involved in detecting the bitter taste of the chemicals caffeine, quinine — that bitter taste in tonic water — and propylthiouracil, or PROP, a synthetic chemical not naturally found in food or drink.