The Chemical Difference Between Red, Yellow, and Green Bell Peppers

We’re going to let you in on a little secret: A green bell pepper is just an unripe yellow pepper, which is just an unripe red pepper (though some varieties ripen to yellow, not red). The same is true for green olives, which are unripe black olives, and the seeds inside green beans are just regular beans that haven’t grown up yet. The produce section is apparently full of lies.

The differences in bell pepper taste, appearance, and aroma are not genetic but chemical, as the ripening process releases a series of colorful, delicious natural compounds. 

As the latest great infographic from Compound Interest shows, peppers do go through three distinct traffic-light stages, each with its own chemical components. In its green form, a pepper is especially plant-like, packed with chlorophyll and “green-smelling” aldehydes. Yellow and orange peppers take their color from lutein and beta-carotene, the chemicals responsible for the sunny and orange hues of egg yolks and carrots, respectively. As a pepper reddens, it begins producing more (E)-2-hexenal and (E)-2-hexanol, which give it a sweet, fruity smell.

Want to watch your own peppers change color? You can leave them to ripen on the plant in your vegetable patch, if you've got one, or you can bring them in (or buy them) and store them in a perforated bag or box in a dark, cool room for a few weeks.

Click the infographic to get a more detailed look.

Image credit: Compound Interest // CC BY-ND 4.0

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