Affordable fuel from grasses, trees and plant waste that packs enough of a punch to power a plane? Scientists said Wednesday this can be done using chemistry to boost basic fermentation processes.

A team at the University of California in Berkeley said it had developed a method to add carbon atoms to biofuels obtained from fermentation -- currently not potent enough to replace gasoline, jet fuel or diesel.

Using the same 100-year-old biological process employed in ethanol production, the team manufactured alcohol and acetone by fermenting sugars obtainable from anything from grasses, trees, corn, sugar beets, sorghum or even plant waste, according to a study in the journal Nature.

The alcohol and acetone is then put through a catalytic chemical process to boost the number of carbon atoms from two per molecule, as in traditional ethanol, to between seven and 15, co-author Harvey Blanch told AFP.

This is similar to the carbon mass of current jet and diesel fuels.

Using similar raw materials, "you get a better product than ethanol for the same price," said Blanch.

"With the same amount of sugar, we make a fuel that is much more effective than ethanol for the same price of the sugar."

Writing in Nature, the team said it had developed "a high-yield method for transforming readily accessible fermentation products from a variety of carbohydrates into precursors for petrol, diesel and jet fuels.

"The integration of extractive fermentation with chemical catalysis is thus a novel and potentially enabling route for the economical conversion of biomass into liquid transportation fuels."

Blanch said ethanol, the most commonly used biofuel, is not very efficient as it cannot be transported in oil pipelines and so has to be moved by truck, and does not mix well with diesel.

Also, "ethanol does not have as much energy per gallon as some of the other fuels".

The new method should address these problems, but has so far only been used on a small, laboratory scale.

"We've produced enough to have it tested in test engines, several litres," co-author Dean Toste said.

"How far we are from making it viable? The chemistry probably needs some work. But one could imagine that this could be viable in a couple of years."

Added Blanch, the new product would be more expensive than current petroleum-derived fuels, but competitively priced compared to some of the alternatives.

"It could be viable if policy is put in place... that will force products like this into the market place," he said

The European Union said last month it was cutting targets for the use of biofuels so as to reduce the negative impact on food production and prices.

Critics said the measure did not go far enough while a UN official called on the EU and the United States to abandon biofuels altogether as land used to produce them was needed by farmers to grow food instead.

About 40 percent of maize in the United States goes into energy production, a state of affairs some say is contributing to food shortages and rising prices.

"This (new) process can use a variety of raw materials, sugars from different sources. We could use waste wood, for example, to do this or other sources of sugar that do not compete" with food, said Blanch.