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ETHANOL FROM KUDZU

Kudzu (Pueraria lobata) is a climbing, semi-woody, perennial vine in the pea family. It is native to southern Japan and southeast China. The name comes from the Japanese word for this plant, kuzu. The other species of Pueraria occur in southeast Asia.

Kudzu plants grow rapidly, spreading as much as 20 m (60 ft) per season at a rate of about 30 cm (12 in) per day. They may extend 10–30 m (30–100 ft) in length, with base stems 1–10 cm (1–4 inches) in diameter and fleshy tap roots 10–20 cm (4–8 in) or more in diameter, reaching depths down to 4 m (12 feet) and weighing as much as 180 kg. As many as thirty stems may grow from a single root crown. Kudzu can thrive under a wide range of conditions and soil types, especially where average temperatures are regularly above 27 °C (80 °F) and annual rainfall is 1000 mm (40 in) or more. It does not do as well in less temperate areas.

Kudzu was introduced from Japan into the United States in 1876 at the Philadelphia Centennial Exposition, where it was promoted as a forage crop for goats, cows, and pigs and as an ornamental plant. Up to the early 1950s the US Soil Conservation Service encouraged farmers in the southeastern United States to plant kudzu to reduce soil erosion. The US Department of Agriculture removed kudzu from its list of recommended ground cover plants in 1953, when it became recognized as an aggressive nuisance, and listed kudzu as a noxious weed in 1972. Infestations are heavy in the Deep South and also in the Florida Everglades, where near-perfect conditions encourage kudzu to grow out of control — hot, humid summers, frequent rainfall, temperate winters with few long freezes and no natural predators.

A kudzu patch looks like a uniformly colored blanket of dark-green leaves, swallowing everything in its path, horizontally and vertically. The leaves, grouped in threes, are 3 to 10 inches long and can have as many as three lobes with hairy undersides. Depending on climate and sunlight, kudzu may flower from  July to September, bearing hanging clusters of purple blossoms that smell like grapes. Seedpods, which appear later, are hairy and bean-like. In winter or after a hard frost, kudzu vines may turn brown, leaves withered or absent. In very warm areas, leaves may remain evergreen.

This plant is quickly becoming a major problem, because kudzu kills other plants by smothering them and blocking their sunlight. Climbing vines can girdle  and eventually uproot trees. It threatens agricultural and timber production.  It is quickly spreading to more and more counties and states and countries.

Why are people looking at the nuisance kudzu as a possible important new source of bioethanol? Because it has a high starch (meaning sugar) content, with long, thick underground roots, around the diameter of an adult forearm, storing plenty of starch usable for ethanol production. In China and Japan, the starchy roots have long been used for cooking and thickening sauces, as well as medicinal products from vines and leaves. Now, there is evidence that kudzu can be used in part to replace corn to make ethanol.

There may be upwards of 7 million acres of kudzu in the country of no use yet. It grows a foot a day, 60 feet a season and can be harvested twice a year without loss of foundation. Just a fragment of the plant remaining in the ground is enough to allow it to come back next season.

The roots are by far the largest source of carbohydrate in the plant: up to 68 percent carbohydrate by dry weight, compared to a few percent in leaves and vines. Cellulose — the woody, fibrous carbohydrate that gives structure to the stems and leaves — can be converted into ethanol with yeast.

Some researchers estimate that kudzu could produce 2.2 to 5.3 tons of carbohydrate per acre. This translates to 270 gallons of ethanol per acre, comparable to the ethanol yield of corn of 210 to 320 gallons per acre. In other terms, 900 to 2500 liters of ethanol can be produced per hectare of kudzu, compared to 2000 to 3000 liters per hectare of corn.

Kudzu is the kind of stock the U.S. needs to be working with because it is a weed, not an essential food crop in our human food supply. Kudzu needs nothing to grow – no planting, no fertilizer, no irrigation. The deep tap root of the kudzu vine can help hold the soil in place and allows the plant to prosper during dry spells, as opposed to corn, whose growth is dependent on sufficient rain fall and irrigation water.

At present, even if equipment were available that could harvest the kudzu roots, a large fraction of kudzu vines blanket steep hillsides and would be difficult to access. Some experts estimate that about one-third of kudzu plants in the US would be harvestable. If so, they calculate that kudzu could offer about 8 percent of the 2006 U.S. bioethanol supply. However, if existing corn ethanol manufacturing plants could be used to process kudzu, too, then the approach might be economical sooner. Kudzu is not tied to the commodities markets, so the price would not fluctuate as much.

Most of the kudzu plant can be used after harvesting.  Even leftovers can accumulated and processed.  No part need go wasted. It is added to animal feed and compost. The fibers can be made into textiles. Kudzu has been put into soaps and lotions.

The non-woody parts of the plant are edible. Young leaves can be used for salad or cooked vegetable; flowers can be pounded and fried; and the starchy roots can be prepared as any tuber vegetable. When added to water and heated, kudzu powder becomes clear and adds stickiness to the food. The purple flowers of Kudzu are also used to make a sweet jelly, with a golden yellow color, and are an excellent honey source.

In traditional Chinese medicine, kudzu is considered one of the 50 fundamental herbs. It is used to treat tinnitus, vertigo, and superficial heat close to the skin surface. The starchy roots are ground into a fine powder for varieties of herbal medicines. Its leaves are high in vitamins A and C, as well as calcium and protein.

In the West, recent medical studies have shown that kudzu can reduce both hangovers and alcohol cravings. People who take kudzu will still drink alcohol, but they may consume less than if they had not taken it. The mechanism may have to do with both alcohol metabolism and reward circuits in the brain. The Harvard Medical School is studying kudzu as a possible way to treat alcoholic cravings, by turning an extracted compound from the herb into a pharmaceutical drug.

Kudzu also contains a number of useful isoflavones, including daidzein (an anti-inflammatory and antimicrobial agent), daidzin (a cancer preventive) and genistein (an antileukemic agent). Kudzu is a unique source of the isoflavone puerarin. Kudzu root compounds can affect neurotransmitters (including serotonin, GABA, and glutamate) and show promise in treating migraine and cluster headaches.

Of course, kudzu mash can make liquor.  One expert has claimed that with a brush cutter, a wood chipper and a homemade still, he could produce a barrel of drink or fuel for under $80.

ETHANOL FROM KUDZU