It’s not surprising that terpenes and terpenoids are responsible for the strong, soapy taste of carrots when you consider the fact that they are the usual culprits for many other strong flavors in fruits and vegetables. A common terpene that you’re probably used to smelling is d-limonene, the compound found in citrus peels that is responsible for that characteristic pungent flavor as well as its effectiveness in cleaning solutions. In addition, many terpenes are directly used in the production of synthetic fragrances in perfumery.
Knowing that, it’s probably not hard to imagine that too much terpene could result in bitter soapiness. The list of terpenes directly identified as responsible for the bitterness of certain carrots includes beta-myrcene, an intermediate commonly used in synthetic essential oils, as well as synthetic fragrances in household products. Although it is difficult to clearly prove, its distinctly resinous and green odor – as well as its bitterness when gathered in high concentrations – makes it a likely contributor to the soapy odors or tastes of carrots.
One proven cause of high levels of terpenes and terpenoids in carrots is the general growing temperature. Studies show that while carrots grown at higher temperatures have the highest sugar content, they are consistently more bitter than carrots grown in colder conditions due to a higher concentration of terpenes. Other possible causes, such as exposure to other fruits or early harvest, have been suggested, but there is little research to determine why or how these factors might lead to higher concentrations of terpenes.