Wheat School: How good is that falling number test?

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Damp or rainy weather just before or during harvest can spell trouble for mature wheat kernels. All that extra moisture can cause sprouting and, if that happens, the kernel produces an enzyme that can drastically affect the quality of the end uses of the crop.

“When wheat begins to sprout, it produces an enzyme called alpha-amylase,” says Dr. Bin Fu, wheat research scientist with the Canadian Grain Commission. “The elevation of alpha-amylase activity can significantly reduce wheat quality by degrading the starch for food processing.”

Falling number is the time (in seconds) it takes for a plunger to fall through a heated, gelatinized slurry of ground wheat meal and water. It’s also the internationally accepted method for indirectly measuring alpha-amylase activity says Fu, and it’s an indicator for quality loss.

The falling number test was standardized back in the 60s, and there are three international standards today: the AACC International Method 56-85 which is widely used in North America, the ICC method 107, and the ISO 3093 method. All three methods are very similar, says Fu, and all use seven grams of ground whole wheat meal, suspended in 25 millilitres of water. The most common protocol used is the AACC method.

Even though the methods are standardized, the same sample or lot can have a lot of variation. One factor that can have the largest effect on the end result is sampling — the sample should be well mixed and must be representative of the field, the bin, or the truckload. How that sample is subsampled and ground can also affect the end number. (Story continues below video)

It’s recommended that 250 to 300 grams of wheat are ground, then the seven grams are measured from that subsample. The grind type and the end particle size will affect the outcome, as well as having the correct weight of wheat meal, the correct amount of water dispensed, and even how the tubes are shaken.

“Even the altitude of the lab doing the test will have an impact on the falling number, because altitude impacts the temperature for water’s boiling point,” says Fu. “In Western Canada, that’s usually not the problem, and actually the method specifies to adjust the falling number, if the altitude is above 310 metres.”

Doing the test more than once, and at least in duplicate, ensures a more accurate falling number result, and Fu recommends that each lab performing falling number testing should routinely check instruments against a standard.

“Improving sprout resistance has been an important objective for wheat breeding programs in Canada for many years,” says Fu. Any new variety has to be equal to or better than the check for falling number when it’s registered.

Related: Do you know the falling number of your wheat crop? 

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