Archive Article: 1998/06/20
Ensuring your wheat meets the specifications for export should now be easier, thanks to recent research. Sarah Henly reports.
WHEN French scientist Marcel Chopin designed a wheat quality test in the 1920s, he couldnt have known that it would survive into the next century.
Indeed, when you hear the criticisms of UK millers and bakers, you wonder how it has done so. Complicated to use, time-consuming, expensive, and prone to giving variable results, to name but a few.
The UK industry has its own assessments of dough suitability for bread and biscuit making. But the Chopin measurement of dough strength and extensibility remains one of the most important tests for processors on the continent. And any UK growers wishing to export wheat to Spain, Portugal and Italy must meet the specifications, says Dr Julian South, research consultant at ADAS Rosemaund in Herefordshire.
European millers have been known to reject UK grain if it doesnt reach their Chopin standards. That may seem harsh considering the uncertainty in the industry on whether it should apply to crops grown under UK conditions. But overseas buyers hold the reins so it remains a requirement.
Dr South is involved in an HGCA-funded project, led by ADAS and carried out with the Campden and Chorleywood Food Research Association, where there is considerable experience of using the Chopin Alveograph. The test measures the energy and time required to inflate a sheet of dough and to burst the bubble formed.
In the process, two important quality measures are collected, the configuration ratio or pressure against time, known as P/L, and the deformation energy called W. For bread production, P/L must typically be less than 0.6 and W greater than 170. For biscuits, P/L should be less than 0.5 and W less than 110.
To maximise the chance of meeting these specifications, UK growers must first select a wheat variety which suits the export market for the end use intended, says Dr South.
The chances of each popular variety meeting the Chopin requirements has been monitored for some years by British Cereal Exports. Over three years of testing, the bread wheat Hereward typically gave a P/L ratio of 0.56 and a W score of 214. And Riband passed the biscuit requirements with a P/L of 0.39 and a W of 74. Rialto, however, wasnt so lucky during that period, failing the P/L test for bread wheat.
Evidently, despite selecting the most suitable variety, an element of chance still exists, warns Dr South. That is what prompted the HGCA to initiate a study to identify the field conditions most suitable for good Chopin Alveograph characteristics. Of the numerous factors investigated (see table), the following were shown to be most important in meeting the required specification – site, soil water availability, nitrogen inputs, and to a lesser extent, sowing date.
The Chopin scores varied considerably between the three sites in the trial. Mercia winter wheat was grown in the same way on a silty clay loam, a chalky boulder clay and a well-drained, stony loam. It came nearest to requirements on the latter site, but the variability was large, explains Dr South.
"We suspect that soil moisture and rainfall during grain filling influence scores on the different sites, which means it is difficult to predict the outcome. However we do know results from other trials suggest that drought leads to unacceptably high Chopin scores. So even where you have picked a suitable variety, you should avoid sowing it in very light, well-drained soils," he suggests.
Apart from variety choice, there are perhaps only two ways in which growers can help to ensure Chopin scores are met. The first, sowing date, is thought to have a minor effect, with later sowing improving the P/L ratio.
However, two extremes – mid-September and early November – were compared in the trial, and there was no effect on the W value. Dr South expects there to be little difference within the optimum timings of late September to late October.
A more consistent way to influence Chopin results could be to optimise nitrogen application rates. In one series of trials using Riband, which normally makes the continental biscuit grade, nitrogen rates of up to 420kg/ha (336 units/acre) were applied. Increasing the rate up to 135kg/ha (108 units/acre) showed a decrease in P/L, and from then onwards it remained fairly stable. The W score increased as nitrogen rates increased further, but stayed within the specifications.
Since the aim with a biscuit wheat is a low P/L and W score, Dr South can see the benefit in using at least 135kg/ha of nitrogen, to ensure P/L is not sub-optimal. For bread wheat, where a high W score is desirable, the same would appear to be prudent.
However, he stresses that those nitrogen rates worked for one variety grown on a clay soil in harvest year 1996. "Further trials must be done before we can make across the board nitrogen recommendations. Having said that, we believe growers could improve their chances of producing export quality wheat by using a little more nitrogen than is needed for yield," he concludes.
Factors investigated in the study to identify the conditions needed to meet the Chopin requirements:
• Site – including climate/soil type
• Soil water availability using irrigation
• Nitrogen application rates from 0 – 420kg/ha
• Position of wheat in the rotation
• Sowing date of mid-September or early November
• Seed rate ranging from 250-500 seeds/sq m
• Lodging control using a growth regulator or none
• Crop shading using ADAS Terringtons covers
Assessments carried out to ensure that the study was dealing with a grain sample of sufficient quality to meet UK requirements:
• Grain specific weight
• Moisture content (corrected to 14%)
• Protein content
• Hagberg Falling Number
• SDS
• Zeleny
• Chopin Alveograph
If youre growing wheat for the export market, youll have heard of Chopin Alveograph scores. P/L and W are measures of protein quality important to European millers and bakers.
UK growers must meet the Chopin specifications if they wish to sell their wheat for export.
Choosing a variety suitable for continental bread and biscuit making is the first step to ensure that. Advice on varietal suitability is available from the National Institute of Agricultural Botany (NIAB) and various other professional organisations.
But even with expert advice and the most reliable of varieties, there is no guarantee that you will make the grade. Recent HGCA-funded research has shown that Chopin Alveograph results are influenced by a number of factors including site, soil water availability and nitrogen applications to the growing crop.
Keeping within the specifications may mean avoiding drought-prone soils and ensuring nitrogen inputs are optimised, the work suggests.
Although further research is needed to confirm the findings, it may be wise to review your soil type and nitrogen fertiliser policy before deciding where to grow wheat for export.