Green Botanica · Tea Guide
Clitoria ternatea
Anchan · อัญชัน · bunga telang
Butterfly pea is a climbing plant of the pea family with flowers of deep sapphire blue. Across Southeast Asia they colour drinks, rice and sweets. Dried, they make a caffeine-free tea that is blue in the cup and turns violet with a squeeze of lime; finely ground, they become a blue powder for drinks and baking.
Meet the plant
Butterfly pea is a perennial climber of the pea family, Fabaceae. Its thin stems twine through fences and shrubs, and each leaf is made up of usually five to seven smooth, oval leaflets. Like other legumes, it carries its seeds in narrow, flat pods, around ten to a pod, and its roots form nodules that take nitrogen from the air.
The flower is the reason it is grown. In the common single form, one large, rounded petal, the banner, opens in deep blue around a white or pale yellow centre. Double-flowered plants carry several petals in a ruffled whorl. Besides deep blue, there are pale blue, violet and white forms.
The flowers open in the morning, and on farms they are picked by hand every day.
Dried flowers steeped in hot water: cha dok anchan, a blue, caffeine-free tea.
Nam dok anchan: the infusion sweetened and finished with lime, which turns it violet.
Rice and sticky rice coloured with the flowers, as in Malaysian nasi kerabu.
Thai khanom chor muang, flower-shaped dumplings, and Peranakan kueh such as pulut tai tai.
Since 2021, a water extract of the flowers has been permitted as a blue food colour in the United States.
Blue gins, lemonades and cocktails that turn violet or pink when acid is added.
The story
Butterfly pea has no single homeland story. It travelled the tropics with people, and its history lives in gardens and kitchens — and, more recently, in food science.
Where butterfly pea first grew is not known. Researchers suggest it arose in or around the Indian Ocean; today it grows throughout the tropics, and Kew lists it as introduced in Thailand.
Carl Linnaeus named the plant Clitoria ternatea, after Ternate in the Moluccas, the Spice Islands of eastern Indonesia, where his specimens came from.
Dan Beach Bradley’s Thai dictionary describes anchan as a climbing vine with khiao or white flowers, and notes that they have no scent.
In Australia, the variety Milgarra was released for pasture and hay. As a legume, butterfly pea also enriches the soil with nitrogen.
Thailand approved the variety Thepratanpailin 63 in 2018, and in 2021 the US Food and Drug Administration permitted butterfly pea flower extract as a natural blue food colour.
In Thailand, butterfly pea is above all a colour. It turns nam dok anchan blue, tints rice and sweets, and colours khanom chor muang, the flower-shaped dumplings of the royal kitchen, whose dough a little lime turns violet.
In Malaysia, nasi kerabu from Kelantan and Terengganu is rice coloured blue with bunga telang. In Peranakan kitchens of Malaysia and Singapore, the flowers colour kueh such as pulut tai tai and kueh salat. Blue was once thought an unlucky colour for food; it became welcome when served with golden kaya.
From flower to pouch
Butterfly pea likes warmth and sun and climbs readily over trellises and fences. Its flowers open in the morning, so on farms they are picked by hand every morning. Weather matters: in cloudy spells, and in very hot or cool weather, the plants give fewer flowers.
Seedlings are planted out and trained up trellises or fences. In Thai trials, the first flowers of Thepratanpailin 63 were picked about a month after planting.
Flowers are picked one by one as they open. One grower in Maha Sarakham, north-east Thailand, gets about 1 kg of dried flowers from 10 kg of fresh ones.
In strong sun the flowers dry in about a day; drying for longer harms the colour. In studies, freeze-drying kept the colour best, and hot-air drying at 60–70 °C did better than slower drying at 55 °C.
Dried flowers are packed in bags that keep out the light, to protect their blue.
The science of colour
The blue of butterfly pea comes from pigments called ternatins. They belong to the anthocyanins, the family of pigments that colours blueberries, red cabbage and red grapes. Many anthocyanins look red or purple and fade quickly in neutral water; ternatins are unusual because they stay blue. Like other anthocyanins, they change colour with acidity, so one cup of tea can turn from blue to violet to pink.
Very strong acid
A squeeze of lime or lemon
Plain tea
A little baking soda
Laboratory only
Ternatins carry several side chains that fold over the coloured part of the molecule. This shields it from water and shifts the colour towards blue.
Add lime or lemon and the pigment changes form: the cup turns violet and, with more acid, pink. Baking soda pushes it the other way, towards green.
In one study, a neutral solution kept half its colour for about 334 days at 4 °C, but only about 18 days at 50 °C. Strongly acidic and alkaline solutions faded faster.
Tea & kitchen
| Tea | Plant · part used | Main pigment | In the cup |
|---|---|---|---|
| Butterfly pea | Clitoria ternatea · flower | Ternatins (blue anthocyanins) | Sapphire blue; violet with lime |
| Roselle | Hibiscus sabdariffa · calyx | Delphinidin and cyanidin anthocyanins | Ruby red and tart |
| Safflower | Carthamus tinctorius · florets | Safflower yellows, such as hydroxysafflor yellow A | Clear golden yellow |
Our powder is the dried flowers, finely ground — not an extract. Sift it and mix it to a paste with a spoonful of water first, as ground flowers do not fully dissolve. Start with a little and add more for a deeper colour.
Recipes
A Thai classic and blue jasmine rice to start with, then new ideas for the colour.
Nam dok anchan, made with dried flowers
Pour just-boiled water over the flowers and leave for 5–10 minutes, until deep blue. Strain, sweeten and let it cool. Serve over ice and add the lime at the table: blue turns violet.
A simple home adaptation
Steep the flowers for 15 minutes in 200 ml of the measured water, just off the boil, then squeeze them out. Cook the rinsed rice with the blue water, the rest of the water and the salt. Rest, covered, for 10 minutes.
The colour of butterfly pea in new uses — not Thai tradition:
Sift 1½ teaspoons of powder, mix to a paste with 1 tablespoon of water, whisk into about 500 ml of hot milk and sweeten with honey.
Fill a glass with ice and lemonade, then slowly pour cooled butterfly pea tea on top; it turns violet.
Steep a few flowers in gin until it turns blue, then strain. Tonic or lime turns the drink violet to pink.
Steep about 10 flowers in 500 ml of warm cream for 15 minutes, strain and set it as panna cotta. Serve with a tart berry sauce.
Beyond flavour
Butterfly pea is first of all a colour, but it also has a place in folk tradition and in research.
Two small Thai studies have given people drinks made from butterfly pea flower extract, together with a single meal or sugary drink:
BMC Complementary and Alternative Medicine · 2018
Human study · small trial15 healthy men drank 1 or 2 g of flower extract in 400 ml of water, with or without 50 g of sugar. With the sugar drink, the rise in blood glucose and insulin was smaller for a short time. The extract was made by boiling dried flowers for hours and spray-drying the liquid — not the same as a cup of tea.
Biology · 2021
Human study · small trial16 men with overweight or obesity ate a high-fat meal with 1 or 2 g of extract. Only with 2 g was the rise in blood fats (triglycerides) smaller and antioxidant status higher. The overall glucose response and the inflammation markers measured did not differ.
Educational product information. Not medical advice. If you are pregnant, breastfeeding or taking medication, consult your doctor before using a new botanical product.
