Understanding grain quality
Buyers purchase small grains based on quality factors that indicate how these grains will perform or function in their intended end use. Uses a range from an animal feed ingredient to a food ingredient after milling, malting or other types of processing.
Grading standards and tests
Over the years, grading standards and tests based on physical and/or chemical characteristics have been developed to measure this end-use quality.
The Federal Grain Inspection Service (FGIS) establishes and maintains the U.S. grain standards to provide uniform inspection.
The official grade includes:
Presence of foreign material or contrasting classes.
Damaged or shrunken kernels.
Additional quality tests
These official standards bind all elevators, which must use FGIS-approved methods when grading grain. Elevators often perform additional quality tests. These tests were added in response to specific market quality needs not currently addressed by the U.S. grain standards.
Although not part of the U.S. grain standards, FGIS prescribes approved methods for these quality tests. Examples include:
If you dispute a quality test outcome used to determine your grain’s grade and quality, you can appeal and have FGIS or an FGIS-approved service provider test the sample. As the food processing industry becomes more competitive and automated, additional quality tests likely will be implemented to control processing and final product quality.
Moisture content is an important factor for determining storability and handling, but also for establishing factors based on specific moisture basis. For example, wheat protein is reported on a 12 percent moisture basis.
Test weight measures the grain density in a bushel and is the primary quality test for determining grade. This is because it’s an indicator of how much flour can be extracted. Wheat with a high test weight has large, plump kernels that result in high milling or flour extraction with fewer bran particles or specks.
Protein isn’t an official grading factor, but it’s a fundamental criterion for establishing economic value.
Hard red spring wheat (HRSW) is usually traded on a 14 percent protein basis because most domestic and international markets purchase it to produce high-protein flour for bread products that require high gluten levels. HRSW also is blended with lower-protein wheat to boost the bread’s baking quality.
Durum wheat protein also is very important. It needs to be 13.5 percent or higher to produce 12.5 percent protein pasta.
Gluten refers to the protein complex that forms during the dough-mixing process. Gluten proteins provide the cohesive, visco-elastic and gas retention properties of bread dough, producing the open crumb structure of wheat breads.
Gluten quantity and quality vary with the six U.S. wheat market classes and determine the functionality or end-use quality. Low-protein or low-gluten wheat varieties (i.e., soft white or soft red winter) are preferred for cakes, cookies, crackers, and pastries. High-protein or high-gluten wheat varieties (hard red spring and hard red winter) are used for breads, rolls, tortillas, and other baked goods.
Tests for gluten quality and other indicators
Gluten quality is commonly determined using a Farinograph, an instrument that simulates the dough-mixing process. Important results include absorption (optimum water needed), peak time (optimum mixing time) and mixing stability (amount of time before dough breaks down). The latter two give processors valuable information on gluten strength.
Other tests measure dough extensibility. Varieties with strong gluten need to be extensible, so dough can be easily handled and processed.
Processors—especially in export markets—want to specify gluten properties when purchasing wheat. Currently, there’s no quick and market-applicable test to accurately test at vessel-loading.
However, FGIS is developing a quick gluten functionality test. In the future, wheat buyers may be able to specify gluten properties in their purchasing contracts, providing more consistent quality from shipment to shipment.
Falling number test
The falling number (FN) test was developed in the 1960s in Sweden. Like grain protein, it’s not part of the U.S. grain standards. The FN test indirectly determines the amount of sprout damage by measuring the amount of alpha-amylase activity in a cereal grain sample.
Sprout damage decreases the quality of bread, noodles, and pasta. Buyers typically consider FN values over 350 seconds to be a sound crop, while values below 300 are often discounted. Certain varieties have inherently low FN values. Thus, low FN values are possible even without visible signs of sprouting.
Deoxynivalenol (DON) is a mycotoxin produced by Fusarium head blight (FHB) that’s concentrated in the bran. DON is in the class of mycotoxins called vomitoxins. DON and vomitoxin are often used interchangeably. In years with high incidence of FHB, grain is routinely tested for DON levels.
FDA advisory levels for DON are 1.0 ppm for food grain products. Wheat is often discounted or rejected if the DON values are 2.0 ppm or higher, as milling typically removes 50 percent or more of the mycotoxin. FHB-damaged wheat has lower milling yield and contains enzymes that break down proteins and reduce the gluten strength, lowering bread and pasta quality.
Barley’s two main uses are feed and malt. In addition, a small percentage of barley produced is used for food (pearled barley) or as a companion/hay crop.
When producing for feed and malt, variety selection is important. To sell a barley variety as malt, the American Malting Barley Association (AMBA) has to approve it as malting barley.
Malting is a biological process that alters the physical and chemical properties of the kernel’s endosperm. Malting can be divided into four stages.
Cleaning and grading: Foreign material and broken kernels are removed, then the clean barley is graded according to size. Different kernel size fractions are malted separately because of different rates of water uptake and germination. The thinnest kernels aren’t malted.
Steeping: After it’s cleaned and graded, barley is steeped in water to raise the moisture content to approximately 45 percent.
Germinating: Upon reaching the desired moisture content, barley is germinated for four to five days under carefully controlled conditions. During germination, some of the enzymes—which are synthesized within the kernel—break down cell walls and a portion of the protein and starch in the endosperm.
Drying: When this breakdown has adequately progressed, the germination is stopped by drying the grain to 4 or 5 percent moisture. The resulting product is called malt.
Malt is the principal ingredient used in brewing and the major source of fermentable sugars. Malt also provides amino acids needed by the yeast, protein for beer foam and compounds that contribute to beer flavor and color.
In the initial stage of brewing, known as mashing, ground malt is extracted in water. Barley components that were solubilized during malting are extracted. In addition, enzymes developed during germination continue to break down endosperm components. During mashing, the most important reaction is the conversion of endosperm starch into fermentable sugars.
Perhaps the most important malt quality parameter to the brewer is the level of malt extract. The level of extract is of great economic importance because it determines the amount of beer that can be produced from a given amount of malt.
In modern malting varieties, approximately 79 to 81 percent of the malt can be extracted into solution. Principle components of malt extract are fermentable sugars, but it also contains proteins, peptides, and amino acids.
Malting barley market standards include approved varieties for malting, as well as quality requirements the grain must meet. Test weight, and minimum or maximum limits for protein, germination, foreign material, skinned and broken kernels and thin barley are all part of the U.S. grain standards.
Germination of malting barley must be equal to or higher than 96 percent. Barley with low germination doesn’t properly modify during malting, reducing the level of malt extract. Low germination or dead kernels also cause other problems, such as poor filtration.
Factors that can negatively impact germination include:
Skinned and broken kernels.
Excessive drying temperatures.
Poor grain storage conditions.
Six-rowed malting barley kernel plumpness should exceed 70 percent. Kernel plumpness is a good indicator of potential malt extract, as plumper kernels have a greater ratio of endosperm to hull. More endosperm indicates more starch and thus greater malt extract.
Kernel plumpness is one of the yield components. Early planting and reducing disease incidence will favor kernel plumpness. High nitrogen rates will reduce kernel plumpness, even with high grain yield.
Grain protein content
Grain protein content for malting barley must be between 11 and 13.5 percent. Protein is important for a number of reasons.
First, there’s an inverse relationship between protein and malt extract. Higher-protein grain tends to be thinner, have a low endosperm-to-husk ratio and yield less malt extract. Second, it’s more difficult to malt. Malts produced from high-protein barley will yield beer with color and haze problems.
Early planting will improve your chances of getting lower grain protein. Excessive nitrogen will increase grain protein above acceptable limits. However, some varieties (e.g., Foster) may meet grain protein specifications under conditions of excess nitrogen.
Skinned and broken kernels
The upper limit for skinned and broken kernels is 4 percent. Kernels are considered skinned and broken when they have:
A third or more of the hull removed.
A hull that’s loose or missing over the germ.
Part or all of the germ missing, or are broken.
Skinned kernels absorb water at a faster rate during steeping, and a high percentage of skinned kernels result in uneven growth during malting. Further, the husk protects the growing shoot during malting. When the shoot is exposed by skinning, it’s easily broken off, and germination stops.
Skinned kernels also seem to be more susceptible to mold growth. Broken kernels are removed by cleaning, but this represents a loss to malt companies. When broken kernels aren’t removed, it has similar effects on malting and brewing as poor germination.
Because of these concerns, malting barley quality specifications limit the level of skinned and broken kernels. Skinned and broken kernels are most often the result of poor threshing or rough grain handling. Paying close attention to combine settings and grain transfer equipment usually helps avoid these problems.
When selecting and managing oats, it’s important to consider whether it’ll be used as a companion crop to establish legumes, or as a grain crop to be used for feed and milling.
If used as a companion crop, short- and early-maturing varieties with good lodging resistance are preferred because they improve the chances of a good legume stand.
If used as a grain crop for feed and milling, note that the standards for milling oats often are more rigid than the U.S. grain standards. Buyers generally are looking for clean, plump, white, bright kernels and high groat percentage.
Test weight is the primary quality test for determining grade and it’ll give the processor an indication of oat groat yield after dehulling. In addition, kernel and groat color are important, with white-seeded varieties often preferred. Weather- or heat-damaged grain is discounted or rejected by millers.
The actual groat percentage and groat composition (which include protein, oil, and beta-glucan levels) also are important quality factors. Oat groat protein content is very important, as many consider oat protein to have higher nutritional quality than other grains.
Oats have higher oil content than other small grains, making it more attractive as animal feed. However, oats grown for food should be lower in oil so it's less likely to become rancid and produce off-flavors.
Factors that impact grain quality
Varieties differ genetically for quality traits, such as grain protein, test weight, and gluten strength. In addition, weather conditions impact the expression of quality traits.
First and foremost, grain protein is negatively correlated with grain yield. This means varieties with the highest grain yield potential generally have a lower grain protein percentage.
The physiology of grain fill causes this negative correlation, which has proven to be very difficult for breeders to change. Thus, your market approach may influence variety selection. High-quality wheat will generally yield less. For an equal or better return per acre, quality premiums will need to offset the lower grain yield.
Differences in gluten functionality due to weather can be extreme. Warm and dry conditions during grain fill result in strong gluten properties, even with low grain protein content. In contrast, cool and wet conditions lead to lower grain protein content and weak gluten properties.
Reviewed in 2018