Heavy rains during the 1999 wheat harvest in North Dakota and
Minnesota resulted in weathered and sprout-damaged wheat, and subsequent market
discounts. I have been asked many times since what impact sprouting has on wheat quality and—what is a falling number?To explain why sprouting is damaging, we need to
talk a little about the germination process. Germination of wheat generally occurs after the kernel has matured and moisture levels have dropped to around 12 to 15%. Water adsorption is
the first step in germination and initiates many biochemical processes; such as, activation and synthesis of enzymes, one in particular is alpha-amylase.
Starch is degraded to glucose, protein to amino acids and oil to fatty acids. This process is necessary for growth of the embryo. The degradation of the starch and protein in the wheat endosperm results in
flour or semolina that produces inferior quality products.
Since durum and bread wheat are used differently, the effects of sprouting on the end products are different. However, sprouting results in lowered
test weight of both crops. Sprouting in durum result in increased cooking loss, softer cooked spaghetti, increased speck count and decreased
spaghetti shelf stability. Sprouted bread wheat results in dough stickiness or bread loaves with gummy insides and large voids. Sprouting in bread
wheat also results in less water absorption during dough preparation, resulting in decreased bread yield.
Compounding the problem is the fact that sprout damage—the
germination process—can affect the inside composition of a kernel even though it the exterior of the kernel appears sound. Sprouting may not be visible but alpha-amylase levels may be considerably elevated.
A falling number test is used to detect this sprout damage. Alpha-amylase breaks down the gelatinous structure that forms from the starch in the
flour. The falling number is a measure of the time required for a plunger to fall through a slurry made from a specified amount of flour and a specified
volume of water. This slurry is maintained at a temperature favorable for enzyme activity. The time in seconds that is required for the plunger to fall
through the slurry is the unit of measurement. The lower the falling number, the greater the sprout damage.
Generally speaking, falling numbers above 300 indicate no sprout damage;
falling numbers between 200 and 300 indicate some sprouting; and falling numbers below 200 indicate severe damage.
There are subtle indicators to look for when sprouting is suspected but not
visible. Weathered kernels, of course, is the first clue. Additionally, weather conditions that lead to sprouting also favor development of fungi that cause black point. Wheat with a weathered appearance and black
point is likely to also have sprout damage.
Sprouting counts as "damaged kernels" when grading wheat. U.S. No. 1 grade wheat can have up to 2% damaged kernels while No. 2 wheat can
have 2.1 to 4% damaged kernels. Wheat graded No. 3 can have 4.1 to 7% damaged kernels, No. 4 wheat can have 7.1 to 10% and No. 5 wheat can tolerate 10.1 to 15% damaged kernels.
The only way to prevent sprout damage is by timely harvest. Of course, most want to harvest their crop as soon as possible after it matures, but as
illustrated by the untimely rains this year, that's not always possible. Sprouting will not increase in storage. However, wheat put in storage at high moisture levels will have severe mold problems.
If you have sprouted grain, consult a market advisor or your local elevator manager to help direct the best avenues for marketing. Grain that is severely sprouted (over 10%) may need to be fed or sold as livestock
feed.
Since sprouting obviously can have negative impacts on the viability of seed, it also may have ramifications on the 2000 growing season if you use
bin-run seed. The germination process can be initiated multiple times in wheat but each time this occurs, the viability of the seed will be reduced.
A germination test should be done if there is a concern about sprout damage to a seed lot. If the test indicates germination under 85%, consider using a different seed source or dramatically increasing seeding
rates. Severely sprouted seed will result in reduced seedling vigor.
