Senay Simsek Research Website


Kernel Analysis

FGIS determines the quality of wheat through standardized testing methods in accordance with the Official U.S. Standards for Wheat (Appendix 1 on page 26) and FGIS Grain Inspection Handbook Book II, Chapter 13, which can be found on the GIPSA Web site at https://www.ams.usda.gov/sites/default/files/media/Book2.pdf. FGIS is required to test for a number of factors. Some of the required factors affect the numerical grades U.S. No. 1 through U.S. No. 5 and U.S. Sample Grade, and some do not. The grade-determining factors are: test weight, heat damage, total damaged kernels, foreign material, shrunken and broken kernels, total defects, wheat of other classes, contrasting classes, and sample grade criteria. The other required factors which are non-grade-determining are wheat class, dockage, and moisture. Official testing service is offered for other "optional" tests such as protein, falling number, single kernel hardness, and mycotoxin and pesticide residue analysis. FGIS provides these testing services upon request in the sales contract. Such optional tests are also available from private unofficial inspection companies.

Grade-Determining Factors

Test Weight per Bushel
Test weight per bushel is the weight of the grain required to fill a level Winchester bushel measure 2,150.42 cubic-inch (35.24-liter) capacity. The factor “test weight per bushel” is determined using an approved apparatus, which has a kettle capacity of one dry quart (1.101 liter). This determination is made on the basis of 1,350 grams of wheat cut from the representative sample using a Boerner Divider. To determine test weight, the work sample is poured into the closed hopper centered over the kettle. The valve is quickly opened to allow the grain to fill the kettle. A standard stroker held in both hands with the flat sides in a vertical position is used to remove the excess grain from the top of the kettle with three full-length, zigzag motions. The kettle is carefully placed on the scale platform. The weight is read by an electronic scale that converts the gram weight to either pounds per bushel or kilograms per hectoliter. Test weight per bushel is a grading factor. Generally, it is expressed in pounds per Winchester bushel, but upon request it will be converted and reported in kilograms per hectoliter.

Shrunken and Broken Kernels
Shrunken and broken kernels is a grading factor for wheat. To determine shrunken and broken kernels in wheat, the inspector places 250 grams on a 0.064 × 3/8 inch (1.626 mm × 9.545 mm) oblong-hole sieve and mechanically shakes the sieve 30 times from side to side. The machine used to sieve the sample, a Strand Sizer, has a stroke counter and always starts and stops in the same position. One complete stroke takes approximately 1 second.

Damaged Kernels
Damaged kernels is a grade-determining factor and is composed of two categories: heat damage and total damage. Heat-damaged kernels are reported separately from all other types of kernel damage but are included in the total damage. The inspector visually examines a portion of the wheat sample — 50 grams for heat damage and 15 grams for other damage types — to determine whether any kernels have been materially discolored or damaged by physical or biological factors.

Foreign Material
Foreign material is a grade-determining factor. It is determined on a 50-gram portion after the removal of dockage and shrunken and broken kernels. The inspector manually removes all material other than wheat. The inspector must be well trained and capable of distinguishing different types of damage. Those conditions that may be mistaken for damage (such as dirt stains which appear to be mold) must be recognized also.

Visual Grading Aids
FGIS maintains a visual grading aids system which serves as the foundation for the national inspection system’s subjective quality control program, providing an effective management tool for aligning inspectors and assisting them in making proper and consistent subjective grading decisions. The system consists of a series of commodity specific visual reference images (VRI), which includes descriptive text, and interpretive line prints (ILP). With regular use, these visual references help to control and diminish the impact of ordinary perceptional differences. VRI focus on individual kernel inspection criteria, whereas the ILP serve as a visual reference in the assessment of the commodity’s general appearance or overall color. A special sample box is used to compare the grain being graded with the ILP. To compare the sample with the ILP, place the 5- × 7-inch photographic print in one side of the box and the grain in the opposite side. This allows for the comparison of the grain and the ILP under similar conditions. On the reverse side of each print is an explanation of the condition illustrated on the photograph and procedures for use of the photograph and box. The only ILP for wheat is for the color of hard white wheat, applied only upon request. VRI and ILP are available for viewing at all official inspection service provider facilities; they can also be viewed on-line by visiting GIPSA’s Web site at https://fgis.gipsa.usda.gov/default_home_FGIS.aspx. When viewing images on-line, it is important to remember that the hardware (monitor, graphics card, etc.) used to display images influences the appearance or color accuracy of those images. As a result, the images may have a slightly different appearance when viewed on different makes/models of computer and display. Visual reference images and interpretive line prints are available for purchase from Seedburo Equipment Company in Chicago, Illinois (www.seedburo.com). The following is a list of the available visual reference images for wheat damage:

  • W-1.0 Black tip damage (Fungus)
  • W-2.0 Scab damage
  • W-3.0 Frost damage (Blistered)
  • W-3.1 Frost damage (Candied)
  • W-3.2 Frost damage (Discolored black or brown)
    W-3.3 Frost damage (Flaked)
  • W-4.0 Germ damage
  • W-4.1 Mold damage
  • W-4.2 Germ damage (Bleach method)
  • W-5.0 Green damage (Immature)
  • W-6.0 Heat damage (Durum)
  • W-6.1 Heat damage (Other than durum)
  • W-7.0 Other damage (Mold)
  • W-8.0 Sprout damage
  • W-8.1 (A) Insect chewed, (B) Sprout sockets
  • W-9.0 Weevil or insect bored
  • W-9.1 Insect chewed wheat (Not damaged)
  • (W) OF-17.0 Unknown foreign substance (Pink wheat)
  • (W) OF-23.0 Smut in wheat (Tagged ends)
  • (W) OF-30.0 Threshed and unthreshed kernels

Total Defects
Total defects, a grade-determining factor that is determined as a further measure of quality, is the sum of shrunken and broken kernels, foreign material, and damaged kernels.

Contrasting Classes
Contrasting classes is a grade-determining factor that is assessed on a 15-gram portion after the removal of dockage and shrunken and broken kernels. Contrasting classes are:

  1. Durum wheat, soft white wheat, and unclassed wheat in classes of hard red spring wheat and hard red winter wheat.
  2. Hard red spring wheat, hard red winter wheat, hard white wheat, soft white wheat, soft red winter wheat, and unclassed wheat in the class durum wheat.
  3. Durum wheat and unclassed wheat in the class soft red winter wheat.
  4. Durum wheat, hard red spring wheat, hard red winter wheat, soft red winter wheat, and unclassed wheat in the classes hard white wheat and soft white wheat.

Wheat of Other Classes
Wheat of other classes is a grade-determining factor that is assessed on a 15-gram portion after the removal of dockage and shrunken and broken kernels. The inspector picks out classes of wheat that are not the predominating class.

Mandatory Non-Grade-Determining Factors
Moisture and dockage are two quality factors that must be determined, but do not affect the numerical grade.

The Grain Analysis Computer Model 2100 (GAC 2100), manufactured by Dickey-John Corporation, Auburn, Illinois, is the official moisture meter for the national inspection and weighing system. The GAC 2100 is calibrated to the USDA air-oven method (1 hour at 130 degrees Celsius ).

Dockage is determined with a special machine called the Carter Dockage Tester. Dockage, like moisture, does not influence the numerical grade. It is an additional test made by the inspector and reported separately on the certificate. The Carter Dockage Tester, using aspiration (air) and a combination of riddles and sieves, prepares a sample for grading by removing the readily separable material. Generally, this material consists of all matter that is lighter than, larger than, and smaller than wheat. The material removed by a dockage tester is readily separated and does not require the additional sophisticated equipment found in the cleaning houses of mills.

Optional Non-Grade-Determining Tests
Customers may require additional quality tests. These optional tests can be performed by private unofficial inspection laboratories or officially by FGIS. Check with the supplier, FGIS, or U.S. Wheat Associates on the availability of any of these optional testing services. FGIS can officially test for protein, falling number, single kernel hardness, aflatoxin, vomitoxin, fumonisin, and certain pesticide residues. Unofficial laboratories can perform additional optional tests, such as, wet gluten, sedimentation, alveograph, farinograph, extensigraph, mixograph, and 1,000-kernel weight. Any optional testing must be requested in the sales contract.

FGIS uses near-infrared transmittance (NIRT) spectroscopy to determine protein for official inspections. FGIS adopted the combustion nitrogen analyzer in 1994 as the standard reference method for determining wheat protein because it provides accurate and consistent results, uses no hazardous chemicals, and has a short analysis time FGIS’ wheat protein laboratory is certified ISO 9002 compliant by the International Standards Organization. All field NIRTs are calibrated to the standard protein reference method, the Combustion Nitrogen Analyzer, to ensure the accuracy of the results. Each NIRT instrument is checked for accuracy daily using a set of six standard reference samples. If the daily average of the results on the standard reference samples differs by more +/- 0.10 percent, the instrument is adjusted and rechecked before use. The goal is to have a daily tolerance within +/- 0.05 percent difference. The same set of standard reference samples is used throughout the FGIS national system for checking official NIR instruments. The Combustion Nitrogen Analyzer consists of a computercontrolled, closed-system, combustion process, and a thermal conductivity detector. Protein is usually reported on the 12.0 percent moisture basis. Upon request in the sales contract, FGIS will report protein on an alternate moisture basis, in addition to the 12.0 percent moisture basis.

Carter Dockage Tester
Large Material
Light Material
Small Material
Protein can be specified by the buyer in the following ways:

  1. Ordinary protein: any protein level can be loaded,
  2. Average protein: a weighted or mathematical average of
    the sublots with no limit on sublot variability
  3. Minimum or maximum protein with a weighted or math average of sublots where Cu-Sum  applies with limits on sublot variability, or
  4. Modified minimum or maximum protein — sublots are weighted or mathematically averaged with a reduced Cu-Sum breakpoint. For example, a request for Northern Spring wheat, minimum 14.0 percent protein, with no sublot below 13.8 percent; or Soft White wheat, maximum 9.0 percent protein, with no sublot above 9.2 percent. The grade and protein are issued on the same certificate. For exammple, if a maximum 10.0 percent protein is specified, the lot average cannot exceed 10.0 percent, no sublot can be higher than 10.5 percent, and all sublots must be within 1.0 percent of each other.

Falling Number (Hagberg)
Falling number analysis is an indicator of kernel germination (sprouting) and the resulting increases in alpha amylase activity. Falling number results of 300 seconds or higher usually indicate that minimal amylase activity due to sprout damage is present. FGIS performs falling number tests as an optional service under the Agricultural Marketing Act (AMA) and reports results on the Commodity Inspection Certificate. Upon request, FGIS determines the FN in wheat meal at the FGIS Technical Services Division Laboratory in Kansas City, Missouri, and certain FGIS field offices and state agencies. Falling number results are reported on a 14 percent moisture basis unless the buyer specifies another moisture basis. Cu-Sum averaging is not available for falling number tests because falling numbers are not additive. Buyers can specify falling number tests in the following ways:

  1. Cargo lot analysis where a single analysis is performed
    for the entire cargo,
  2. “Liquefaction average” of sublots, or
  3. Sublot minimum analysis where a limit is placed on each sublot.

Single Kernel Characterization
Studies have been conducted under experimental milling conditions which show that single kernel characterization information can be used with other data such as test weight to provide an accurate prediction of the milling performance of a wheat sample. Such information may be useful to identify wheat for purchase that will perform better under processing conditions. Specifically, the Single Kernel Characterization System (SKCS) analyzes exactly 300 wheat kernels from a 15 to 20- gram portion that is free from dockage, shrunken and broken kernels, and foreign material. Individual kernel size, weight, moisture, and crushing profile (hardness) are measured and displayed on a histogram. It also reports the range, average, and standard deviation for each of the four factors.

FGIS performs hardness testing as an optional service under the AMA and is reported on the Commodity Inspection Certificate.

Information source: "Wheat and Flour Testing Methods: A Guide to Understanding Wheat and Flour Quality: Version 2"


Wheat Quality & Carbohydrate Research
Department of Plant Sciences
NDSU Dept. 7670
PO Box 6050
Fargo , ND 58108-6050
166 Loftsgard Hall
(701) 231-7737
Fax: (701) 231-8474
Site Manager: Senay Simsek
Last Updated: