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Virginia Cooperative Extension - Knowledge for the CommonWealth

What is a falling number and what does it mean about your wheat?

Crop and Soil Environmental News, June 2007
Wade Thomason, Extension Grains Specialist and Kelly Burt, Graduate Student

A particularly wet harvest season in some areas in 2006 has drawn attention to the topic of pre-harvest sprouting in the mid-Atlantic region.  According to the U.S. Wheat Associates report, “Relatively high damaged kernel values and low falling numbers in the East reflect the difficult harvest conditions there, while very good values were recorded in other states.”  Last year’s flour data reflected a decreased falling number average.  In 2006 the falling number average for east coast wheat was 260 seconds a 25% decrease from the five year average of 347 seconds.  Figure 1 shows wheat falling number ranges for the eastern US and the Gulf from 2006.  

A falling number test measures the level of alpha amylase activity that has occurred within a grain sample.  Released as seeds sprout, alpha amylase is an enzyme that degrades starches within the seed, greatly reducing flour quality.  Falling number tests are conducted by creating a slurry from ground wheat flour and water.  Sound grain (high falling number) produces a thick slurry because the starches are still in tact.  Sprout damaged grain will result in a flour/water mixture that is “thin” or non-viscous because the starches have began breaking down due to the alpha amylase activity.  The time for a plunger to move through the slurry to the bottom of a test tube is measured.  The faster the plunger reaches the bottom of the test tube, the lower the viscosity of the mixture (thinner) and the higher the alpha-amylase activity or sprout damage.

In general, values below 300 seconds are indicative of poor quality for milling and baking purposes.  Sprout damaged grain can affect mixability, crumb strength, sliceablity, and volume.  Wheat that does not meet the minimum falling number standard is unsuitable for milling and is usually sold to the livestock feed market.  Flour quality wheat generally receives a premium of $0.40 or more per bushel over feed wheat.

Figure 1.  Wheat falling number values for the 2006 crop.  US Wheat Associates Report.


Earlier studies have demonstrated that pre-harvest sprouting is partially controlled by genetics.  Lines with white seed coat color are generally more susceptible to sprouting than those with red seed coats.  We intend to evaluate current commercial and experimental wheat lines available in Virginia for their resistance to sprouting in the coming year. 

Environmental conditions both before and after seed maturity influence the rate of pre-harvest sprouting.  In general, the more wetting and drying cycles the seed experiences, the more likely it is to break dormancy and sprout.  This type of weathering also decreases grain test weight which is another important component of wheat quality evaluation. 

To minimize pre-harvest sprouting and test weight losses, harvest and dry wheat the first time it reaches 20 percent moisture or the first time it reaches 15 percent moisture if drying is not possible.  Make sure the combine and all other critical equipment including hauling capacity are “ready to roll.”  Try not to let other steps in the harvesting chain limit the combine capacity per day.  Set the combine properly and modify the cylinder speed and/or concave clearance as harvest conditions change during the day.  Timely harvest is absolutely critical if milling quality wheat is to be produced.


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