Pinpointing wheat varieties for bioethanol
As a large biorefinery in north-east England nears completion, Andrew Blake examines work under way to create wheats more specifically for its and others’ consumption
About 1m tonnes of the UK’s next wheat harvest are expected to be used by the Ensus Group’s £250m biofuel production plant at Wilton on Teesside, according to ADAS’s Daniel Kindred.
A similar amount from the 2010 harvest is likely to be required by Vivergo’s wheat-to-bioethanol plant at Saltend, Hull. And further proposed bioethanol plants at various UK sites could eventually absorb 2.6m tonnes annually, says Dr Kindred.
The plants’ main stimulus has been the EU and UK’s targets for reducing carbon emissions from road transport. “But their commercial operation doesn’t all hinge on bioethanol prices,” he stresses.
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| This new outlet for UK wheat should be producing bioethanol fuel later in 2009. |
Technically the distillation process is well known. Scotch whisky producers have long employed it, currently using about 800,000t/yr of wheat, says colleague Richard Weightman.
Researchers from ADAS, the Scottish Whisky Research Institute and SCRI have been examining how the breeding and agronomy of wheat might be directed more specifically for this purpose in a number of HGCA projects.
A key conclusion is that grain needs a lot of starch to get a high alcohol yield, which means low proteins, says Dr Weightman. “But we also need to show how to get that while minimising greenhouse gas (GHG) emissions.”
The lower the GHG emissions the greater the environmental benefit of using biofuel, he explains.
Production and use of nitrogen fertiliser accounts for over 70% of the GHGs created in growing wheat, so optimising N applications for wheat grown for bioethanol is a key target, as is producing varieties that require less nitrogen.
Analysis of over 100 wheat nitrogen response trials over different soils, varieties, sites and seasons shows that the optimum N for alcohol production per hectare is about 10% less than that for optimum grain yield.
Those optima are clearly influenced by the ratios between the relative prices of N fertiliser, grain and ethanol. Dr Kindred says that the more costly N becomes, the less N fertiliser should be used and the more valuable the grain becomes for bioethanol.
At some point growers producing wheat for the new biorefineries will probably need to undergo some form of auditing, maybe through ACCS, to confirm the GHG savings of their production methods, he adds. And given that arable land is limited it’s important that any savings are expressed per hectare rather than per tonne.
“In theory the maximum GHG savings could come by applying as little as 50kg/ha of nitrogen. But if we want to avoid encouraging forests to be cut down for biofuel production elsewhere in the world the optimum is going to be much more.”
The amount of alcohol produced differs greatly between varieties, and not just because of starch content, says Dr Weightman. Other constituents vary also, such as the fibre fraction. “One of our roles is to gain a better understanding of what’s going on with these other components.
“The best predictor of alcohol yield remains protein content, though in the GREEN grain project we are developing a near infra-red calibration that could be used at grain intake or in breeding programmes.”
There is still a long way to go, he admits. Traditionally only soft milling varieties are screened for their suitability for distilleries. Yet the new bioethanol plants will inevitably take in hard wheat types as well.
Little is known about the suitability of hard feeds though, which is why HGCA-funded work has started at ADAS Boxworth to look at their alcohol yields. It’s likely that the range in alcohol yields and processing quality in the generally higher yielding and widely grown hard milling types is even greater and needs determining as soon as possible to assess their value for the new bioethanol market, the two researchers conclude.
