Low Falling Number: Causes and Solutions in 2019

Below are some answers to questions you might hear at the local coffee shop as growers begin making decisions about wheat varieties to plant.

“Why is wheat tested for falling number?” 
Falling number, is the result from the Hagberg falling number (FN) test, certified by American Association of Cereal Chemists International (AACCI) to test for the presence and activity of alpha-amylase enzyme in ground whole grain meal.  The wheat industry uses the number as an estimate of the end-use functionality of flour made from the grain. Alpha-amylase is an enzyme that breaks starch into simple sugars. This process is called hydrolysis. The FN test is a proxy for pasting quality (thickening ability) used by the industry to manage the risk of buying grain that has poor quality starch. Any result below 300 seconds is considered low and may result in a deduction, often 1 cent per second below the 300 line, from the price of a bushel of wheat. The application and calculation of this deduction is not consistent across elevators or grain buyers. Deductions for low FN is entirely up to the purchasing agent.

“What causes an increase in alpha-amylase enzyme in my wheat?” 
After flowering, wheat is focused on filling the developing seed with reserve carbohydrate energy in the form of starch. Recent studies have confirmed that wheat is very sensitive to changes in temperature and moisture during grain filling. Mature grain can also begin to germinate when exposed to free water (rain) or heavy dew. Presently low falling number are considered the result of pre-harvest sprout (PHS) and late maturity alpha-amylase (LMA). These two situations have been well-defined in literature. PHS is incorporated into wheat grading standards set by the U.S. Federal Grain Inspection Service.

In PHS, fully mature grain is exposed to moisture and the seed begins to germinate on the plant or in the seed bag. The process of germination breaks down the endosperm (starch) using alpha-amylase enzyme, into simple sugars, destroying the pasting ability of the starch from the grain. LMA is very different from PHS. When wheat is exposed to high temperatures during the day and very low temperatures at night, approximately 25 to 30 days post-flowering, another type of alpha-amylase forms in the aleurone (bran) layer. LMA can result in a low FN but is generally not below 250 seconds.

LMA was identified as the cause of low FN test results across wide areas of Idaho and the Pacific Northwest (PNW) in 2011 and 2016. In 2014, extended August rains in the Snake River plain during harvest caused widespread low falling number from sprouted wheat (PHS) creating an industry-wide crisis. In 2016, PNW farmers estimated they lost $140 million due to low FN discounts to their wheat crop.

“Does it matter if the low FN is caused by LMA or PHS?”
Yes, it matters in terms of the effect it will have on the functional quality of flour from the affected grain. A growing body of scientific evidence shows that the type of alpha-amylase induced by LMA is in the bran layer, does not move out of the bran and has different enzyme characteristics than the alpha-amylase involved in germination. The PHS alpha- amylase, activated during germination, migrates through the starch and breaking the starch into simple sugars to provide energy for the developing sprout.

“Why does LMA cause a low FN test result?”
LMA alpha-amylase in the bran layer is removed in the milling of refined flour, which limits the impact on pasting quality in refined flour. However, in the Hagberg FN test, the grain is ground whole and the meal tested contains the bran. When LMA type alpha-amylase is present, it contacts the starch molecules from the ground meal and breaks down the starch.

“How does the FN test work?”
When a flour and water mixture is mixed and heated, the starch granules begin to move away from each other and absorb water. As a result, the mixture starts to thicken similar to the process of making gravy. At some point, the thickening process becomes a thinning process, when the mixture is over-heated. Then, the starch molecules burst and release water back into the mixture. Once this happens the starch is destroyed and no longer has the ability to thicken the mixture. The LMA enzyme is stimulated to break down starch at a much lower temperature than the PHS enzyme. In the presence of the LMA enzyme, the starch is broken down earlier in the FN test and reaches maximum heat before the test is completed. This occurs well before the temperature at which the PHS enzyme would break down. The starch broken down by LMA is over-heated in the standard Hagberg FN test protocol. Therefore, the starch molecules burst and release water back into the test tube, thinning down the mixture and resulting in a low FN test result.

“Is a lot of grain that could make good flour discounted or included in the feed market?”
It looks that way. The milling industry knows that most end-users can easily handle flour with a falling number of 250 or above. The industry has started to use the FN test as a risk management tool. The standard is set at 300 seconds to ensure a 50-second margin on all grain purchased. The practice started in the export market between 2005 and 2010 and became standard practice in the export market and much of the domestic grain market.

“How can we tell the difference between LMA and PHS?” 
Currently, there is no simple, quick and easy elevator type of test, but several research and engineering teams have proposed discriminating tests for LMA versus PHS.

“What can I do to limit my risk for LMA or PHS?”
Both syndromes are caused by the interaction of  genetics with climate and production practices. Approximately 30 percent of the risk can be mitigated by choosing varieties tolerant to the climate issues you expect in your field (see Table 1 and 2 below). If you are concerned about experiencing a near-freeze at night in the period of 25 to 30 days post-flowering, you can select varieties that are tolerant to LMA. If your field is prone to getting rain or heavy dew after the grain is ripe and before harvest, you can choose a variety resistant to PHS. Pay attention to the historical daily weather data for fields in order to make an informed decision. If you suspect the field was exposed to environmental conditions that might cause LMA or PHS, have the grain tested before harvest. Today, the industry will discount on low FN regardless of the cause. If you know you have some low FN grain, segregate it as necessary.

“Why should I segregate the low FN grain?” 
The alpha-amylase enzyme is powerful and effective at breaking down starch. Just one grain of wheat with a 100 FN number has enough of the enzyme in it to reduce a 2,500 grain sample of 400 FN wheat by 100 seconds. Low FN grain does not blend off at a 1:1 ratio like protein does. Keep it separate and tell your elevator you have some low FN grain that you need to sell. A good elevator will find a home for it with experts who have the equipment and expertise to blend it away. Do not try blending at home!

Table 1.

Spring Varieties to Reduce Risk for Low Falling Number
Ryan UI Platinum WB9668
WB6430 Dayn WB 9518
  WB7202 (CLP) SY Gun Sight
  WB 7696 SY Renegade
  WB 7329 SY Coho
  WB 7589 Glee
  WB Hartline Jefferson

Table 2.

Winter Varieties to Reduce Risk of Low Falling Number
UI Castle (CL+) UI Silver SY Touchstone
Stephens   Whetstone
NW Duet   UI SRG
LCS Hulk    

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