Kudzu

Pueraria lobata

Puerarin and starch · a root dug from the hillside vine

Kudzu is a legume vine that blankets hillsides, and the part this entry deals with is the thick root running underground. Pounded and pressed, the root gives kudzu juice; steeped in water several times and left to settle, it gives galbun, the starch used for kudzu noodles and pressed tea cakes. Starch lies thick in the root, and analyses have repeatedly isolated isoflavone compounds such as puerarin and daidzein from it. Digging season runs from late autumn once the leaves have dropped through to early spring, because that is when the starch sits heaviest. The Donguibogam lists it in the Herb section as 葛根, giving it a neutral nature with a note that some call it cold, a sweet taste and no toxicity. It grows in the mountains and is found everywhere, the entry says, and the root is dug on the fifth day of the fifth lunar month and dried in the sun, with the deepest-set roots reckoned the best. It is not a crop to plant, though — one crown will smother the trees around it within a few years, and in Korean forests as in the American Southeast the work is all in cutting it back. Buying a soil-covered root at a traditional market is the better route.

Year-Round Calendar

Sowing

Harvest

Where It Grows

Main producer Wild population Latitudes at 20–30℃ Zoom and pan to explore · temperatures are rough zonal averages

Main producer The mountain districts of Central and South China turn out kudzu root and kudzu starch (galbun) in large quantities.
Wild population Common on hill skirts across the country, and dug between late autumn, once the leaves have fallen, and early spring. Harvest November, December, January, February
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Wild population In Yoshino in Nara, and in Fukuoka and Kagoshima, kudzu starch (kuzuko) has long been made from wild-growing roots.
Wild population Southern Primorye is the northern edge of its natural range.

Its native range is the temperate zone of East Asia, spanning the Korean Peninsula, China, Japan and Primorye in the Russian Far East. Stock taken to the southeastern United States in the early 20th century for erosion control and fodder spread beyond containment, and it is treated there as an invasive species, so that region is not listed among the producing areas. For the same reason it is not listed for northern Italy and southern Switzerland, where it has also spread.

Optimum: 20~30℃
Range: 10~35℃
Hardiness: Hardy

On a sunny, south-facing slope, meeting the heat and humidity of summer, the vine puts on a hand's span in a single day. The root runs down more than 1 m, letting the plant endure dry ground and poor soil, and in winter the top of the vine dies back while the plant carries on through the root below ground.

Harvested 2–3 years after planting. Roots divided and planted in spring take two or three years to thicken. Digging falls between November and February, after the leaves have dropped, so the year of planting and the year of harvest are not the same.

In Korea Nationwide

Common on hill skirts and slopes across the country. Most of the crop is dug in the hills rather than planted and grown, and in forest land the vines are cleared away every year.

How to grow

Light: A sunny south-facing slope. The vine runs in shade too, but the root never thickens
Soil and depth: Free-draining slope soil with grit in it. The root goes down over a metre, so a pot is no place for it
Spacing: The rule is not to plant it. If it must go in, keep it five metres from any tree and cut the vines back every year to hold the line
Watering: None given. Once established it carries itself on rainfall alone
Feeding: No feeding. As a legume it fixes its own nitrogen through root nodules, and feeding only lengthens the vine
Harvest: Dig from late autumn after leaf fall through to early spring, when the starch sits heaviest in the root. Work downward from above with a mattock, and fill the hole back in when you are done

What makes the difference. Choose a root with a pale, close-grained cut face that is still moist. Hollow or brown-dried roots give little juice. Store with the soil on somewhere cool, and freeze sliced pieces in portions

Why this one is harder. Planted, it gets away from you. The roots run sideways and keep sending up new vines that smother the trees around them, and in the American Southeast it spread into a notorious invasive. Clearing the vine is annual work in Korean forests too. Better not to plant it in a garden at all

Common problems

Aphids You will see Colonies on the tips of new vine growth, turning sticky What to do Wash them off with a jet of water. Where the root is to be dug for eating, it is better not to spray at all
Mould on dug roots You will see White mould settles on the cut faces of roots left in a plastic bag What to do Wrap them in newspaper with the soil still on and keep them somewhere cool and airy. Slice and freeze in portions

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

The old record — galgeun (葛根). The Donguibogam lists it in the Herb section as 葛根. Its nature is set down as neutral, with a note that some call it cold, its taste as sweet, and it is recorded as having no toxicity. It grows in the mountains and is found everywhere, the entry says, and the root is dug on the fifth day of the fifth lunar month and dried in the sun, with the deepest-set roots reckoned best. Nokgwak (鹿藿) is given as an alternative name. What an old medical text wrote differs from how it is judged today.

Analyses of root isoflavones. Repeated analyses report the isolation of isoflavone compounds, puerarin among them, from kudzu root. The same work reports that levels vary with the part sampled and the season of harvest. This is an analysis of composition.

Starch and galbun. Galbun is the root's storage starch, steeped out in water and settled. That the starch sits heaviest from leaf fall through early spring is handed down as the reason galbun was made in that season. This is a record of a processing method.

Nutrition

Puerarin (isolated from the root) — the signature isoflavone glycoside of kudzu root
Daidzein and daidzin (present alongside it in the root) — isoflavones commonly reported across legumes
Starch (lies thick in the root) — the storage carbohydrate that makes up galbun
Dietary fibre (the coarse grain of the root) — tough fibre that stays behind after chewing

Root starch — galbun Starch lies thick in the kudzu root. Pound the dug root, steep it in water several times and let it settle, and the sediment is galbun, long used for noodles and pressed tea cakes. Galbun is essentially starch, so it differs in composition from a decoction of the whole root. The same plant delivers different things depending on the form it is eaten in.

Isoflavones Analyses have repeatedly reported the isolation of isoflavone compounds such as puerarin and daidzein from kudzu root. Isoflavones are a compound class common across legumes, and research addresses the structural resemblance they bear to human oestrogen. That research, though, has mostly used extracts drawn from the root, a different set of conditions from drinking the juice or the tea. This entry stays with the compositional record.

Tough fibre Kudzu root is coarse-grained and stringy, and chewing does not break it down. That is why it has long been chewed and spat out, pounded for juice, or sliced thin and dried for decoctions. The same fibre is what stays in the sieve when galbun is strained off.

Bitterness and astringency Freshly pressed kudzu juice is bitter and astringent. Roots dug after leaf fall taste sweeter than those dug late in spring, because more starch has settled in them. Mixing in pear juice or honey has long been the way of covering that finish.

Pairings

○ Kudzu-starch noodles and tea cakes — Galbun does not bind well on its own, so buckwheat or wheat flour is mixed in to draw the noodles. For dasik, the pressed tea cake, galbun is worked with honey and stamped in a mould. It becomes a wholly different ingredient in taste and texture from a decoction of the whole root.

○ Honey and jujube — Simmering kudzu with jujube and finishing with honey holds down the bitter, astringent finish. Thin dried slices draw faster than thick pieces. A slow simmer rather than a hard boil loses less aroma. Jujube

○ Ginger — Two or three slices of ginger in the pot add a warm pungency that makes the tea easier to drink. Ginger sharpens the longer it boils, so add it at the end and take the pot off the heat. Ginger

△ Do not dig on land that is not yours — Wild kudzu still grows on land with an owner. Taking forest products from state or private woodland without permission runs against forestry law. Digging a root tears up a slope, and the damage shows. If there is no agreed place to dig, buy it at the market instead.

△ Do not dig a leafless vine on a guess — Kudzu is dug once the leaves have gone, which means identifying it from the vine alone. Kudzu carries leaves in threes, its young stems are roughly brown-hairy, and old vines take on a bark-like surface. The safe order is to confirm leaves and flowers in summer, mark the spot, and dig there in winter. If you are not certain, do not dig.

△ Do not take concentrates, pills or powders like medicine — Studies on kudzu have mostly used extracts drawn from the root, a different quantity and a different form from juice or tea. Anyone planning to take a concentrated form over time should first check it against the medicines they are already on. If a hormone-related prescription is involved, do not add it on your own judgement.

Varieties

Galgeun (kudzu root) (part) — The thick underground root. The raw material for juice and tea, and the part covered here
Galbun (kudzu starch) (processed) — The sediment left after the pounded root is steeped and settled. Used for noodles and tea cakes
Galhwa (kudzu flower) (part) — The purple summer flower. The Donguibogam entered it separately from the root
Kudzu shoots (part) — The young vine tips of spring, blanched and dressed as a namul

Source: Donguibogam, Herbs section (Chobu), Galgeun (kudzu root)