Why blueberries are blue

What is that color due to? Why are blueberries blue? That almost philosophical question was asked by researchers from the University of Bristol. They revealed that small external structures in the wax layer of blueberries give them their blue color. The same thing happens in plums, sloes and juniper berries.

The study was published in 'Science Advances'. There researchers show why blueberries are blue. And this happens despite the dark red color of the pigments in the fruit's skin.

Why are blueberries blue?
Why are blueberries blue?

blue ultraviolet

Instead, its blue color is provided by a layer of wax that surrounds the fruit. It is made up of miniature structures that scatter blue and ultraviolet light. This gives blueberries their blue appearance to humans and their ultraviolet blue appearance to birds. Where does blue-UV chromatic reflectance come from? From the interaction of randomly arranged crystalline structures of wax with light.

Rox Middleton is a researcher at Bristol's School of Biological Sciences. He explains in a statement: “The blue in blueberries cannot be 'extracted' by crushing them. It is not found in the pigmented juice that can be squeezed from the fruit. That's why we knew there must be something strange about the color. So we removed the wax and re-crystallized it on cardboard. By doing so, we were able to create a new blue-UV coating.”

The ultrafine dye is about two microns thick. Although it is less reflective, it is visibly blue and reflects UV rays well. This possibly paves the way for new coloring methods.

The particular properties of their peel make blueberries blue to our eyes.
The particular properties of their peel make blueberries blue to our eyes.

Sustainable paint

“This shows that nature has evolved to use a really clever trick. An ultra-thin layer for an important dye,” adds the researcher.

Knowing why blueberries are blue has practical applications. The team plans to look at easier ways to recreate the coating and apply it. This could lead to a more sustainable, biocompatible and even edible paint that reflects UV rays and blue. Furthermore, these coatings could have the same multiple functions as natural biological ones that protect plants.

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