Tree based brew

20 November 2011
Posted by Dave Ansell.

There is a large amount of energy locked up in all the wood that is left over after your planks and paper have been made, and most of this wood is in the form of soft woods from conifers. You can release the energy as heat in a fire, or in a power station, but if you could convert it into something that would run a car, it would be much more valuable.

It is possible to add enzymes, cellulases, to the wood which will break down the cellulose into sugars, which can then be fermented into ethanol, concentrated and burnt in a car. But these enzymes will only work after the structure of the wood is broken up by heat and chemical treatment. This releases all sorts of chemicals in the softwood, which slow the growth or even kill the yeast. This means that it is only possible to ferment solutions with about 4-5% of wood, and this means that not very much ethanol is produced and it isn't economic to concentrate it enough to burn.

Gary Hawkins and Joy Doran-Peterson from the University of Georgia have been using evolution or at least selective breeding to help with this. They have grown a fairly standard yeast in stronger and stronger solutions of the inhibitory chemicals in the wood, meaning that theyeast which is adapted to this environment survives.

Their strain of yeast can convert 70% of the theoretical maximum amount of ethanol in 3 days and 90% in 5 days, at concentrations up to 17% wood solids. This is much more economic, and with more breeding they could do better. So you may be filling up with fermented pine in not too long.

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