Why Is Butterfly Pea Blue? Why Lemon Turns It Purple

The blue of butterfly pea is the color of a pigment called anthocyanin.
Add a squeeze of lemon, and the blue turns purple — on contact with acid, the pigment changes shape.
And this botanical carries almost no aroma. It is in the tea all the same, because the color itself is built into the design.

What is butterfly pea?

Butterfly pea is a flowering legume. In Southeast Asia it has long been used to color drinks and sweets. Drop the dried petals into hot water and, within tens of seconds, the water turns blue. Few plants give this much blue without borrowing color from anywhere else.

The blue is anthocyanin

This blue is the color of pigments called anthocyanins. They belong to the same family as the pigments in blueberries, red cabbage and red shiso; the kind in butterfly pea happens to be one that shows blue.

Anthocyanins change their molecular shape depending on how acidic their surroundings are. When the shape changes, so does the wavelength of light they reflect. That is why the color moves.

Why lemon turns it purple

In neutral hot water, it is blue. Squeeze in lemon to add acid, and it shifts to purple. With stronger acid still, it drifts from red-purple toward pink.

Red cabbage steeped in vinegar turns a vivid red-purple, doesn't it? Exactly the same thing is happening inside the glass. It is a change you can watch right in your own kitchen.

Pour the tea into a glass of ice first and then squeeze in the lemon, and you can watch the color travel down from the top. It is a move less for the taste than for the eyes.

Why include a botanical with no aroma?

Vetiver Tea Symphony No.1 is made of just three botanicals: vetiver, echinacea and butterfly pea. Of these, the first two carry the aroma.

Butterfly pea, in other words, is an ingredient that takes no part in the aroma design. It is there all the same — to show, in color, the stillness of vetiver, a root herb.

Inspice has one other ingredient that carries no aroma yet takes part in the design: the rock salt in our chai. It works from the side of taste, drawing the outline of sweetness and aroma. Which is to say, designing a flavoring is not a matter of aroma alone.

With three ingredients, provenance steps forward

The fewer the ingredients, the more directly the quality of each one shows. There is nowhere to hide.

The vetiver is naturally grown in Hoshino Village, Yame, Fukuoka Prefecture. The butterfly pea and echinacea come from Pezan Farm at Kahokugata in Ishikawa Prefecture. A design that has to stand on three ingredients is why we choose where each one comes from.

How to brew, and how to use it up

One tea bag brews about 1.5 L. For hot tea, use 400–500 ml of boiling water. A used tea bag can be dried, or simply topped up, and used about three times. As a guide: 5 minutes the first time, 7 minutes the second, 10 minutes the third — steep a little longer with each round.

For iced tea, pour on 1–1.5 L of hot water, leave for about 10 minutes, and refrigerate once cool. It contains no caffeine.

How the other botanicals build their aromas is collected in our Spice Encyclopedia.

Frequently asked questions

Q. Does butterfly pea have a taste or aroma?
A. Almost none. Its main role is the blue color. In Vetiver Tea, the aroma is carried by vetiver and echinacea.

Q. Why does lemon turn it purple?
A. Because the pigment, anthocyanin, changes its molecular shape when the surroundings turn acidic. It is the same mechanism by which red cabbage and shiso change color in vinegar.

Q. Does it contain caffeine?
A. No. Vetiver Tea is caffeine-free. A good choice for a quiet breath at the end of the day, too.