- Type
- Legumes
- Difficulty
- Easy
- Season
- Spring·Summer
- Sowing
- From seed
Hyacinth Bean
Lablab purpureus
Protein and anthocyanins · a climbing bean for a shade frame
Hyacinth bean is an annual climbing legume that carries purple flowers and flat pods right up to the first frost. The vine runs past three metres, so trained over a yard frame or a balcony rail it builds real summer shade while still producing food. The mature seeds, though, must be soaked and boiled thoroughly; this is not a bean where that step can be skipped. The Donguibogam lists it in the Grain section as 藊豆, with the Korean name byeondu-kong. It explains the alternative name 鵲豆, magpie bean, from the white line across the black seed coat, and records that the seed is peeled and tossed with ginger juice before frying.
Year-Round Calendar
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Where It Grows
- Main producer It is grown most heavily in the south, in Karnataka, Tamil Nadu and neighbouring states. It has been a field crop there for more than 4,000 years.
- Major producer Known as sem, it is grown up fences and trellises through the cool dry season.
- Major producer It is grown on the central highlands under the name njahi.
- Major producer It is interplanted among maize and also used as livestock feed.
It is believed to have been domesticated in Africa and to have crossed to India at a very early date, becoming a major crop there. Because its origin cannot be pinned to any single country, no country-of-origin row has been set out. It reached East Asia later, by way of China. In statistics it is lumped in with various pulses, so hyacinth bean is hard to count on its own.
- Optimum
- 22~30℃
- Range
- 15~35℃
- Hardiness
- Not hardy
- Day length
- Short-day
A vine bean of tropical origin, it is killed by a single late frost. It holds up fairly well to heat and drought, and it is a short-day bean, with flowering concentrated from late summer as the days shorten.
In Korea Nationwide
Seed goes in during May once the ground has warmed, and pods are picked until the first frost. It is an annual and cannot overwinter — survive the winter — outdoors in open ground.
How to grow
- Light
- Six hours of direct sun or more. Good light is what brings the flowers
- Soil and depth
- Free-draining field soil. In a container, use one at least 30cm deep
- Spacing
- 40 to 50cm between plants. The vine spreads widely, so do not crowd it
- Watering
- Water in summer once the surface dries. Containers need checking daily
- Feeding
- Rely on the base dressing. Excess nitrogen brings leaf at the expense of flowers
- Harvest
- Pick green pods in August and September, while they are flat and the seeds have not swelled. Leave pods intended for seed until October, when they dry and harden. Frost drops the whole vine at once, so gather what is left before it arrives
What makes the difference. Put the support in before sowing. Driving in a stake after the vine has grown damages the roots
Why this one is harder. Do not rush the sowing date. This is a tropical plant and a single late frost will kill it outright. Sow in May, once the ground has properly warmed
Common problems
- Aphids You will see Colonies on new shoots and flower stalks, with curling leaves What to do Wash off with a jet of water and use an egg-yolk oil spray if it recurs
- Bean bug (Riptortus pedestris) You will see Pods form but the seeds never fill, leaving them shrivelled What to do Hand-collect in the cool of the morning. Watch hardest while the pods are filling
- Powdery mildew You will see White patches spreading over the leaves as if dusted with flour What to do Thin the lower leaves for airflow and avoid watering in the evening
This page describes how a crop is grown and used. It does not claim health effects for any food, nor is it intended to prevent or treat disease. Component and study notes are references only and do not mean the same result occurs in people. Consult a medical professional about health concerns.
Health Benefits
What the Donguibogam records — nature, taste and the magpie bean name. The Donguibogam lists this bean in the Grain section as 藊豆 with the Korean name byeondu-kong. It calls the nature slightly warm, though some say slightly cold and others neutral, and gives the taste as sweet with no toxicity. The entry divides the seed into black and white kinds, calling the white warm and the black slightly cold and reserving the white for medicinal use, and explains the alternative name 鵲豆, magpie bean, from the white line across the black seed coat. It also records the preparation, peeling the seed and tossing it with ginger juice before frying, notes a restriction for those suffering chills and fever, and states that this is what is meant by 白扁豆. This is a historical medical record and differs from modern medical judgment.
Analyses of antinutrients under different cooking conditions. Analyses report that lectin and trypsin inhibitor levels in hyacinth bean seed fall sharply with soaking and sufficient heating. The same work reports that short cooking at lower temperatures leaves substantially higher residues. This concerns compositional change under cooking conditions and has no bearing on preventing or treating disease.
Reports on anthocyanin composition. Anthocyanin pigments have been identified in the deep purple pods and flowers, with analyses reporting wide variation between lines. Observations that the pigment leaches into the water during boiling are recorded alongside. This concerns pigment composition and does not imply a health benefit.
Nutrition
- Protein (20 to 25g per 100g of dried seed) — plant protein typical of legumes
- Anthocyanins (in the purple flowers and pods) — the polyphenols behind the red-violet colour
- Lectins and trypsin inhibitors (present in the raw seed) — antinutrients greatly reduced by thorough cooking
- Dietary fibre (concentrated in the thick seed coat) — polysaccharides fermented in the large intestine
Protein Dried hyacinth bean seed carries 20 to 25g of protein per 100g, within the usual range for legumes. That figure only means anything once the beans are fully cooked, because raw seed also contains proteins that block digestion. Young pods eaten green are mostly water and fibre, with a much lower protein figure.
Anthocyanins The colour of the purple flowers and pods comes from anthocyanin pigments. Boil the pods and the pigment leaches into the water, leaving them green. Analyses report higher pigment content in the darker-coloured lines. Lines sold as ornamentals tend to be the deepest in colour.
Antinutrients in the raw seed Raw hyacinth bean seed is reported to contain lectins, trypsin inhibitors and cyanogenic glycosides. Soaking, discarding the soaking water and boiling hard for long enough removes most of them. A long simmer at low temperature is not a substitute. This preparation is mandatory, not optional.
Dietary fibre The seed coat is thick, which puts the fibre share high. Eaten whole after boiling the beans keep you full a long time, though they also produce gas. It seems no accident that the old text specifies peeling the seed before use. Discarding the soaking water reduces the effect.
Pairings
○ Green pods, blanched or stir-fried — Young pods with the seeds still undeveloped are used like green beans. String them, blanch three to four minutes in boiling water, then stir-fry. A little salt in the blanching water keeps the colour.
○ Cooked into rice — Fully boiled seeds can be mixed into rice. The safe method is to soak overnight, boil them separately until done, then add them to the pot as it steams. Do not put raw seed straight in with the rice.
○ Ginger — The old text specifies peeling the seed and tossing it with ginger juice before frying. A little ginger still cuts the raw bean smell when frying hyacinth bean today. It is an old preparation surviving as a cooking instinct. Ginger
△ Undercooked or raw seed — Mature hyacinth bean seed is reported to contain lectins and cyanogenic glycosides, and eating it raw or undercooked can cause nausea, stomach pain and diarrhoea. Soak overnight, throw the water away, and boil hard with the lid off for long enough. A slow cooker at low temperature is not a safe alternative. Do not taste raw seed straight from the plot.
△ Seed sold as an ornamental — Seed sold for flowers is sometimes treated with fungicide or dyed. If you intend to eat the crop, buy seed labelled for food, and plant ornamental packets without eating what they produce. Seed you saved from your own plot that year is free of this problem.
△ Legume allergy and a first serving — Hyacinth bean is a legume, so people who react to other beans may react to it. It is an unfamiliar bean, so start with a small amount. The Donguibogam also records a restriction, advising against it for those suffering chills and fever. That is a historical medical record and differs from modern medical judgment. Soybean
Varieties
- White-flowered, white-seeded (baekpyeondu) (seed) — Both flower and seed are white. This is the line the old text sets aside for medicinal use
- Magpie bean (purple flower, black seed) (seed) — A white line stands out across the black seed. The name 鵲豆, magpie bean, comes from this
- Ruby Moon (seed) — An ornamental line with deep purple pods. Widely planted for shade frames
Source: Donguibogam, Grain Section 藊豆 · Rural Development Administration (Nongsaro)