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The Magic of Butterfly Pea Tea

The reason why the telltale tea keeps changing colour is pretty basic (and acidic).

The scientific name for the Butterfly Pea plant is Clitoria ternatea, which sounds exactly like what you may be thinking: female genitalia. In fact, its name was inspired by the resemblance of its petals to female reproductive anatomy (which is also why traditional medicine often associates it with libido). The species is native to Asia; the second half of its binomial name is drawn from the Indonesian city of Ternate, where the first specimens were catalogued. This plant boasts a brilliant blue flower that can serve as a natural dye for fabrics and for…tea!

But this isn’t just any old caffeine-free tea. It’s magic. Starting off as blue, the squirt of a lemon turns it violet. Sprinkle some roselle hibiscus flowers and you’ll end up with a red drink. What’s the secret? The tea is an acid-base indicator! It changes hue in response to a change in pH.

The letters ‘pH’ get thrown around quite a bit; they stand for “potential hydrogen.” It is a measure of hydrogen ion concentration in an aqueous solution based on a scale that ranges from 1, which is very acidic, to 14, which is basic. A neutral solution has a pH of 7. By definition, an acid releases protons (or hydrogen ions, H+), so an acidic solution will have many hydrogen ions floating around. A base accepts protons, so a solution of pH 14 has virtually no hydrogen ions. A neutral substance has an equal amount of hydrogen and hydroxide ions (OH-); H+ and OH- combine to make H2O – water. Acids, such as lemon juice, generally taste sour, while basic substances, a solution of baking soda for example, taste bitter.

Indicators are chemicals that change colour in response to a change in pH. A naturally occurring compound in butterfly pea tea is blue at a neutral pH but turns purple and then red as acidic lemon juice is added. If you poured baking soda into the tea, it sure wouldn’t taste good, but you’d get a green-yellow colour. There are also synthetic indicators such as the classic phenolphthalein that is colourless in an acid solution and fuchsia in a basic one. Bromothymol blue is yellow in acidic solutions, blue in basic solutions and green in a neutral solution.

Apart from a cool colour display, what do the flowers of the Butterfly Pea bring to the table? They contain a number of antioxidants, such as kaemphferol, p-coumaric acid, and the anthocyanins that are responsible for the colour changes. Antioxidants neutralize free radicals that are produced by normal metabolic processes and have been linked with promoting diseases and aging.

Butterfly Pea tea may resemble Gatorade but it doesn’t taste anything like it. It is an herbal tea, like chamomile, but with the added chameleon effect. A staple in Southeast Asia, it is now increasingly popular in the West. Butterfly Pea is a key ingredient in a gin originating in Victoria, B.C. – blue in the bottle, but lilac when mixed with acidic tonic water. Few flowers can claim to be as revered, revealing, and intoxicating (in a cocktail) as the humble Butterfly Pea.


Haleh Cohn is studying Anatomy and Cell Biology at McGill University.

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