Falling numbers of wheat and why it matters

We have received a few questions concerning the "falling number" on winter wheat and preharvest sprouting. I thought we would provide some insight around that number. What is it? What causes it to change? Why is it important?

Basically, sprouted grain changes the makeup of the kernel starch content and changes the structure of the starch chains, which in turn influences the quality of baked goods.

What is a "falling number" and how is it done?

When wheat seeds break dormancy and begin to sprout in the head prior to harvest, the quality of the seed can degrade quickly. When sprouting occurs, the alpha-amylase enzyme begins to break down the long chains of starch into simple sugars. This impacts the quality of bread, cookies and crackers made from sprouted wheat.

The amount of alpha-amylase enzyme fluctuates naturally as the seed develops and matures. Discounts for sprouting begin at 2.6% sprouts in the sample at $10.00 per tonne and go up from there.

Falling numbers is a test that helps identify the structural integrity of the starch chains. To conduct the test, grind the grain into meal, add water, mix with a stirrer and add heat for 60 seconds.

The falling number is the number of seconds it takes for the stirrer to fall to the bottom of the test tube. The longer it takes the stirrer to fall, the higher the quality of starch (longer chains).

End-users of wheat (millers and bakers) perform the falling number tests to determine the quality of the flour and use that number to predict the quality of baked goods but to also source wheat of appropriate quality.

Figure 1. Relationship of alpha-amylase to falling numbers. Source: "Causes of low falling numbers in wheat," Camille Steber, USDA-ARS, Washington State University.

Falling numbers

Falling numbers over 250 seconds are most suitable for the bread-baking process. In contrast, falling numbers above 350 seconds may indicate that the flour should be supplemented with a form of amylolytic enzyme or with malted grain flours. Most large-scale bakeries work with an ideal falling number range of 250–280 seconds.

Recently collected soft red winter wheat samples in Ontario subjected to 72 hours of high humidity and constant misting have 2% sprouts developing in less than that time frame. A single rain event after maturity can change a falling number (recent test) from over 300 to 247 or less.

Most wheat varieties, upon reaching maturity, can have seeds dormant for several days. It depends on genetics and environmental conditions during the late grain fill period as to how much dormancy is obtained. Generally, when wheat is ready to harvest, nothing good happens after that. The reason wheat is prone to sprouting is the persistent rains that cause constant wetting, and cooler temperatures in repeated cycles, begin to break dormancy.

For this reason, weather in an area will often determine the degree of sprouting. Some areas with persistent rain may not sprout as much as other areas might; it is the wheat variety and environmentally sensitive activity. This will frustrate everybody in the supply chain.

Something to consider

The weather is challenging for a timely harvest. Often harvesting at higher moisture and paying the drying charges is better than losing the quality and missing the top market values. At 18% moisture, drying charges are $11.00 per tonne. This may be a better outcome than experiencing steep discounts on feed-grade wheat starting at $25.00 per tonne and increasing from there.

Source: "Causes of low falling numbers in wheat," Camille Steber, USDA-ARS, Washington State University.