Falling Numbers 101: Determining Sprout Damage in Grain

 By Brian Sorenson,
Technical Director, Northern Crops Institute Crop Quality Specialist, NDSU Extension Service

The “falling number” is a measurement used by plant breeders and grain quality specialists to determine the soundness of wheat, which is primarily influenced by the degree of sprouting in a grain sample.

Hagberg Falling Number is the full name of this international standard of sprout measurement.  The term “falling numbers” refers to the amount of time it takes for the Hagberg steel ball in this sprout analysis tool to fall through a flour/water slurry that has been heated to release the starch from water. In sprouted grain, enzymes are produced which break down the starch. If there is less starch, the slurry is less viscous (or thick) and the ball falls more quickly. The result is a lower falling number reading. The faster the ball falls through this slurry, the less time it takes, the lower the falling number.

Sprouting in grain can occur once the kernel has reached maturity; therefore, when mature kernel is subjected to proper moisture, temperature and time it begins to sprout.  The physiological changes needed to produce a new plant require energy and nutrients, which is why the wheat kernel produces enzymes to breakdown starch (amylases), oil (lipases) and protein (proteases). This process is exploited in the production of barley malt, which is an enzyme and nutrient “package” vital to the brewing of beer. 

When moisture levels in the wheat decrease prior to threshing, the sprouting process stops, and if it stops before there are visible signs of sprouted kernels it is called incipient sprouting.  The impact of sprouting on foods produced from wheat depends on the amount of enzymes present and breakdown of the kernel. Sprouting lowers test weight and flour yield, lowering the grade and value to the processor.

The impact on baking quality is observed by lower absorption (water added in baking, which reduces bread yield), reduced mixing strength and tolerance, and sticky dough. It can also affect loaf volume, crust strength and crumb texture, whereas a wet and gummy crumb causes problems with slicing and shelf life.  The starch degradation and enzyme activity also reduce the quality of Asian noodles.  The effects on durum are lower test weight, reduced semolina yield and color.  In the processing of semolina and pasta, sprouting increases semolina speck counts, reduces shelf life of dried pasta (due to checking or cracking), increases cooking loss, and produces softer cooked pasta. The level and impact of sprout damage is not fully realized until it is processed into bread or pasta.

The Falling number test does not directly measure amylase enzyme activity, but measures changes in the physical properties of the starch portion of the wheat kernel caused by these enzymes during the test.   

There are actually no standards for falling number, as it is not an official grading factor in FGIS grain inspection and grading process. Generally speaking for wheat, a falling number value of 350 seconds or longer indicates low enzyme activity and very sound wheat.  As the amount of enzyme activity increases, the falling number decreases. Values below 200 seconds indicate high levels of enzyme activity. In the past, grain buyers have discounted wheat for falling number values below 300 seconds.   Falling number values are also important overseas, as many of the buyers from export markets have written minimum tolerances of 300 to 350 seconds into their purchase contracts.  

How to Conduct a Falling Number Test Step 1: Bonnie Jacobson, NCI Food Technologist, prepares a sample for the falling number test. Whole ground wheat or flour and water is added to the test tubes and shaken to form a slurry. Step 2: Stirring rods are inserted into the test tubes, which are placed in the boiling water bath (212 F) in the falling number apparatus. They are automatically stirred for 60 seconds, causing the starch-water slurry to thicken due to starch swelling or “gelatinization.” When starch granules become gelatinized, they are increasingly susceptible to degradation by amylase enzymes, which increases the rate of thinning in the slurry.  Step 3: After mixing and heating, the stirrers are released at the top of the slurry. The falling number apparatus records the time for the stirrer to fall through the slurry.  The rate at which the stirrer falls is directly related to the amount of starch degradation by amylase enzymes. A falling number value of 300 seconds or longer indicates low enzyme activity and very sound wheat.