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Grain grading, and the science behind falling number

The test is an effective way to determine sprout damage in wheat

grain grading in a lab at Cigi

Pre-harvest sprouting or germination of wheat triggered by wet weather during the end stage of new-crop maturity can lead to poor end-product quality. The falling number test is one effective and objective way to determine the extent of sprout damage in a wheat sample.

“Farmers are especially interested in falling number when they come to our courses,” says Rex Newkirk, vice-president of research and innovation for Cigi, the Canadian International Grains Institute.

Cigi uses falling number for its annual harvest assessment and at the request of customers. “Falling number is important but doesn’t measure everything regarding wheat quality,” Newkirk says. “It only measures the effects of sprout damage. Quality characteristics such as protein content, moisture levels, frost damage and plant disease are detected through other methods.”

Canadian grain quality is supported by a process in which wheat must meet certain standards in order to become a registered variety. Quality is also supported by grain grading standards which include visual inspection of sprout damage by Canadian Grain Commission grain inspectors who also look for a number of other downgrading factors including midge, fusarium, and ergot using various procedures outlined in the Official Grain Grading Guide.

However, because visual inspection for sprout damage is subjective, some farmers would prefer falling number testing for grading, Newkirk says. “Possibly because falling number is used heavily in some other countries, there is an impression that it can be used as an objective method for grading. But it only measures sprout damage which activates the alpha amylase enzyme that causes end-product quality issues, especially in baking. The test is also time consuming and there is the additional cost of equipment.”

The recent new crop of durum wheat grown in Saskatchewan was hit especially hard by atypical wet weather conditions, causing higher levels of sprout damage than usual, so it became more of a focus than in previous harvests, says Elaine Sopiwnyk, Cigi director of science and innovation.

“This past year there was such a combination of downgrading factors that the amount of durum grading as number one and two was the lowest that it’s been in the past decade,” Sopiwnyk says. Durum semolina is primarily used for processing products such as pasta and couscous.

“Sprout damage is more of an issue in baking where breads rely on higher water content during processing,” Sopiwnyk explains. The addition of water to the flour sets off the alpha amylase enzyme that affects sugar and yeast activity. This in turn causes excess gas production during the fermentation stage that can impact quality characteristics such as loaf colour and volume, and crumb structure. The quality of pasta from durum semolina can also be affected by sprout damage although usually not as severely since the processing involves lower water content.

The test

The falling number test follows international standards procedures and involves an instrument consisting of a water bath, test tube, and a stirring mechanism. A ground sample of grain, flour or semolina is placed with distilled water in the test tube and shaken. The test tube containing the flour-water slurry and the stirring mechanism is then placed in boiling water and stirred. As the temperature of the flour-water slurry increases, the starch in the sample begins to make the sample more viscous. Meanwhile, any alpha amylase enzyme in the sample will break down the starch, reducing viscosity. After 60 seconds of stirring, the stirring mechanism, or plunger, is released from the top of the tube and the time it takes to reach the bottom is measured in seconds to provide the falling number. The more sprout damage in the grain, the greater the alpha amylase activity which lowers the viscosity, resulting in the plunger falling faster and giving a lower falling number.

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