Many people find beets unappealing because of their distinctly earthy flavor.
The off-putting flavor comes from a compound called geosmin. The same compound is responsible for the aroma the earth gives after it rains and that of freshly dug soil. Humans are particularly sensitive to geosmin and can detect it at even very low -- five parts per trillion -- concentrations. The compound also has a reputation for giving municipal water supplies an off flavor, and can give fish a muddy taste.
Beets high in this compound tend to taste more like dirt. The strikingly beautiful Chioggia beet, with its variegated red and white rings, has more geosmin than other varieties. Low geosmin beets include the varieties Detroit Dark Red and Crosby Green Top.
Other foods containing geosmin include freshwater fish (catfish, carp, trout), spinach and mushrooms.
Adding an acid such as citrus or vinegar can help neutralize the odor of geosmin, thus reducing the earthy flavor.
Sources: chemistry.about.com, grow.cals.wisc.edu, U.S. Geological Survey
Food on 03/18/2015