Grain skinning, the whole or partial loss of the husk at harvest, is a barley defect which reduces malting efficiency by affecting the rate, vigour and evenness of germination, a key feature of the process. As such it affects the whole supply chain, from breeders and growers, through to maltsters, brewers and distillers.
However, ratings on the susceptibility of barley varieties to grain skinning could be included on the AHDB Recommended Lists. This is one possible outcome of a three-year AHDB project* led by SRUC’s Dr Steve Hoad.
“Skinning matters to maltsters because the underlying tissues are less protected during grain handling which can lead to irregular germination. Loss of outer tissues also means water uptake is more direct and therefore faster. This makes germination and conversion of starch into sugars more variable. Bulks with high levels of skinned grain are unlikely to attract a malting premium and vulnerable varieties could lose market share.”
The project supports another**, which is screening many new and older UK and European varieties to pinpoint those with the best resistance. That work, which began in 2013, is also investigating the genetic causes and controls of husk adhesion to help reduce the risk of skinning in future varieties. This collaboration with the James Hutton Institute is due to report next year.
Dr Hoad’s SRUC colleague Dr Maree Brennan has already identified several consistently resistant lines. However, these do not include any of the current leading malting varieties.
“Most modern or recent UK varieties carry some risk. The current market leaders have excellent processing quality but are very susceptible to skinning when triggered by variable weather,” he says. “Some older varieties and some feed varieties appear to have lower risk.”
The AHDB project involves pulling together data on grain skinning from several sources including specific SRUC and Scottish Agronomy trials from harvests 2014 and 2015.
The work suggests skinning is linked to the weather at early grain fill or during ripening.
“We consider periods of episodic wetting and drying might be a particular risk factor,” says Dr Hoad.
“Intermittent wetting and drying causes tension in the grain and affects the adhesion process, so increasing the skinning risk at harvest. It’s also increased by damage during combining and subsequent handling.”
Grain skinning can be difficult to assess. The AHDB project is also working with maltsters to create an industry standard laboratory procedure for scoring skinning. “Guided by a protocol from the European Brewery Convention, our project is trying to improve accuracy and precision of the assessment, as well ensuring it’s time-efficient.”
In 2012 skinning was bad across the UK, when most crops had poor grain fill because of dull wet weather, says Dr Hoad. “Some were rejected because of skinning, and even lower risk varieties were problematic.”
Skinning levels were relatively low for the next two seasons, but the 2015 intakes from some Scottish regions have shown moderate to high levels in popular varieties, he says.
“Even in a low skinning year, there are significant differences in skinning among different varieties.”
Results from the AHDB work indicate grain skinning is equally prevalent across brewing and distilling varieties.
“Initially, it was thought brewing-only varieties were more resistant than distilling or dual-purpose types, but we’ve established this isn’t the case. This came as a surprise to some in the malting sector.”
Other findings show early sowing and early harvesting produce lower skinning levels than late sowing and late harvesting.
“To date, there’s no evidence pesticides or plant growth regulators influence skinning, but limited evidence suggests high nitrogen supply can increase it.”
So far the work suggests skinning is not directly linked to varietal differences in grain size or weight, i.e. to bold – versus small-grained types. However, treatments which cause under-filled grains do increase the amount of skinning, adds Dr Hoad.
“Careful choice of combine harvester settings can reduce it, but too slow a drum speed won’t properly remove the awns and can lead to processing problems at the malting house.”
Setting the concave too tightly raises the risk of grains breaking which lowers malting efficiency, and tight concaves and excessive drum speeds also increase skinning, he adds.
Supporting UK malting barley with improved market intelligence on grain skinning
- Lead partner: Dr Steve Hoad, SRUC
- Industry partners: SAC Commercial, Scottish Agronomy, IBD and MAGB
- Funding: AHDB £98,366
- Finishes: September 2016
Causes and control of grain skinning in malting barley: phenotyping and genetic analysis
Funding: BBSRC Crop Improvement Research Club £420,000
- Partner: John Hutton Institute
- Finishes: April 2016
THE 2015 harvest has produced some high levels of grain skinning, says Keith Headridge, commercial director of Scotgrain Agriculture, the direct farm procurement arm of Bairds Malt in Scotland.
“Growers adjusted their combine settings, and in many instances that reduced the skinning levels but it didn’t eliminate them,” he says.
The weather was also clearly involved, Mr Headridge adds.
The sudden drop in grain moisture content – from about 20% to 15% – which occurred in some parts of Scotland over the weekend of September 5-6, resulted in significantly higher skinning levels; but over the next week, when harvested moistures were in the 18-21% range, they fell back.
Combine type may also play a part, with samples harvested with a rotary combine showing significantly reduced grain skinning, he adds.
“Before 2015 we hadn’t seen such a noticeable difference, so this is another factor we may need to consider.
“This is one of the most important research projects the industry has been involved with in recent years; and with the importance of the distilling sector to farmers’ incomes, their cropping and the wider Scottish economy it’s certainly an area where the whole supply chain can benefit.”