Kudzu Starch is an expensive starch used in Japan to thicken dishes with, or to coat foods before frying them.
You can buy it in chunks, flaked or powdered, and in several grades. The most expensive is the pure, white powder, which is 83% starch. A lesser grade is a slightly-greyish colour, and will be more roughly powdered.
Some commercial brands of Kudzu Starch have other starches added to them, to reduce the shelf price.
It doesn't leave a starchy taste in what you have thickened, and is translucent when cooked. Most starches or thickeners (such as agar agar, arrowroot, cornstarch, gelatin and potato starch) are slightly acidic. Kudzu, instead, is more alkaline. Some feel this helps give a more balanced taste when used with sugar (which is acidic.)
Kudzu Starch comes from the underground tubers of the Kudzu (aka Kuza) vine.
In Japan, the vine isn't a seen as a problem, because it's harvested to produce this expensive starch from, but in North America, where the plant is not used for food, it's regarded as a great pest of a weed.
Kudzu was brought to North America as a garden ornamental. It is a perennial, woody, very vigorous vine, that can grow up to 1 foot (30 cm) a day. It can grow from seed, but mostly spreads by runners. It is not frost hardy, but it is drought-resistant. Its underground tubers can survive repeated yearly herbicide application above ground. The tubers also store energy to let the plant regrow from scratch if it's mowed down.
The vines are hairy, with leaves 2 3/4 to 10 inches (7 to 25 cm) long. The vines can spread up to 60 feet (18 metres) a year, and can form a mat over trees up to 8 feet (2 1/2 metres) thick. While this thick, dense foliage is attractive, it stops light getting through to the trees it is growing on. The vine is so strong that it can also pull lines down, or pull power lines, shorting them out.
It blossoms in late summer / early autumn with 1 inch (2 1/2 cm) purple flowers in clusters of 20 to 30, that look a bit like pea plant flowers, and have a pleasant grape-like fragrance. The flowers produce pods with are sometimes empty; sometimes they will have around 10 seeds in them.
Underground, the plant has a tap root that grows down to 10 feet (3 metres) or more. The plant actually enriches the soil around it with nitrogen.
It is cultivated in the Philippines, Malaysia, Indonesia, and Australia (introduced there.)
To harvest it, you dig up the roots. The best tubers are 5 to 10 years old, and will be about 4 to 6 inches (10 to 15 cm) wide, and will weigh about 22 pounds (10 kg.) Kudzu tubers are best harvested from December to March when the plant is at rest, and the sap is concentrated in the roots.
You clean the tubers, cutting the stems off, and mash them into a grey paste. You wash the grey paste several times, filtering it through fine screens to remove fibres and wash away bitter tannins until just a thick, firm starchy sludge is left settled at the bottom of the water. The sludge is often then washed a few more times, with it getting whiter each time. This is then formed into thick blocks up to 6 inches (15 cm)long, and dried at room temperature for 2 months. The drying process can be sped up by machine drying, but this makes the kudzu starch harder to dissolve in water. The blocks are then brushed, crumbled up, and packaged for sale.
Kudzu leaves, when young, can be eaten steamed, pickled, raw, fried, or simmered. The leaves can also be fed to livestock, but they have to be separated from the woody vines (the vines are themselves are strong enough to weave into furniture and baskets.)
Tea can be made from the flower blossoms.
Jellies made with Kudzu Starch hold their shape and sheen for up to 3 days. Noodles can be made from the starch, such as the ones called "kudzu kiri."
Crumble the chunks before using then crush them more finely using the back of a spoon, or in another way, if you wish. Mix the amount of starch you are using first with an equal amount of cold water, then introduce into a hot liquid.
The mixture needs to then be simmered for a few minutes for the thickening power to kick in.
Kudzu possibly first appeared in America at the Japanese pavilion at the Philadelphia Centennial Exposition in 1876, being displayed as a garden ornamental. Then, it was sold to homeowners through mail-order catalogues.
In the 1930s and 40s, farmers were actually paid $8.00 an acre by the Soil Conservation Service to plant Kudzu. The United States Department of Agriculture (USDA) thought it would control erosion, and enrich the soil of over-farmed fields.
It has since escaped cultivation and spread to forests, smothering and killing other plants and trees, even out-competing native North American weeds.
Its woody vine makes it difficult to bale as a fodder for animals. Letting animals eat it directly doesn't work, as they trample it and kill the vine, destroying their food source.
Some people tried to introduce Kudzu into Africa, but it wasn't successful there.