%Thins = Weight of material in pan
                                      250 g                      x 100

The desired Thins percentage will vary by user, though nearly all would prefer less than 50%. An Extended Kernel Size Evaluation is also available.

      The % Horneous Endosperm Test is also offered as a component of the Basic Food Grade Test Bundle.
     This test provides a measure of endosperm hardness to alkaline cookers and dry millers.
     The test is performed by visually rating the kernels, placed germ facing up, on a light table. Soft endosperm is opaque, and will block light. Hard, or horneous, endosperm is translucent. A rating is made from standard guidelines based on the degree to which the soft endosperm at the crown of the kernel extends down toward the germ. Ratings for twenty externally sound kernels are averaged for the reported result.
     Most food grade corn users prefer a result of 90% or higher for the % Horneous Endosperm Test, although some may accept as low as 85%.

Possible Values 70-100%; Typical Results 70-95%

     Test Weight, or bulk density, is also offered as a component of the Basic Food Grade Test Bundle.
     Test Weight is a measure of the quantity of grain required to fill a specific volume (Winchester bushel). There is often, though not always, a strong correlation between Test Weight and True Density. As such, Test Weight is often used as a gauge of endosperm hardness to alkaline cookers and dry millers. High-test weight corn will take less storage space than corn with a lower test weight. Test Weight is a part of the GIPSA Official United States Standards for Grain grading criteria.
     The test involves filling a test cup of known volume through a funnel held at a specific height above the test cup to the point where grain begins to pour over the sides of the test cup. A strike-off stick is used to level the grain in the test cup, and the grain remaining in the cup is weighed. The weight is then converted to and reported in the traditional U.S. unit, pounds per bushel (lb/bu). Because Test Weight can decrease as moisture content increases, the moisture content of the sample is also reported. It is recommended that the sample be between 12 and 16% moisture for analysis. Most food grade corn users desire Test Weights higher than 60 lb/bu with some requesting a minimum of 62 lb/bu.

Possible Values 48-67 lb/bu; Typical Result 56-64 lb/bu

     The Visual Kernel Characteristic Ratings are also offered as a component of the Basic Food Grade Test Bundle. The Visual Kernel Characteristics scores are available individually or as a group of five tests. Twenty individual kernel ratings are averaged to determine the final result.
     There are certain visible characteristics that can convey a great deal about a corn sample’s suitability for food grade corn uses.

Crown Score – The Crown Score is a measure of kernel hardness. It is a rating of the amount of opaque soft endosperm that is deposited at the crown of the kernel. Ratings of individual kernels are made on a scale of 1 (soft endosperm extends half or more of the length of the kernel from the crown) to 9 (no soft endosperm visible at the crown). A rating of 6 (soft endosperm at the crown extends to, but not over, the “shoulders” of the kernel) or higher is preferred by most processors, but will vary.

Possible Values 1-9; Typical Results 4-8.5

Dent Score – The Dent Score is another measure of kernel hardness. As corn kernels mature, soft endosperm at the crown compresses while the hard endosperm remains rigid. This results in a dimple, or “dent”, in the crown. This is reason for the term “dent corn”. Nearly all corn grown in the US is of the dent corn type. Softer corn has a deeper dent. Ratings of individual kernels are made on a scale of 1 (very deep dent with wrinkling of the crown and potential “kissing” as the edges of the dent are pulled to each other) to 9 (no dent). A rating of 6 (the dent is still more of a smooth-edged depression than an abrupt cavity in the crown) or higher is preferred by most processors, but will vary.

Possible Values 1-9; Typical Results 4-8.5

Split Kernel Horneous Endosperm – The Split Kernel Horneous Endosperm Score is yet another measure of hardness. The hard endosperm in corn is preferentially deposited in specific locations within the kernel. The first hard endosperm is laid down on the “back” side (opposite the germ face) of the kernel. As kernels get harder the quantity of hard endosperm at this location increases to a point where hard endosperm begins to be deposited on the germ side (between the germ and the crown) in increasingly larger amounts. This phenomenon is easily observed by splitting a kernel in half through the germ face. Ratings of individual kernels are made on a scale of 1 (no hard endosperm visible) to 9 (very large deposit of hard endosperm between the crown and germ face). A rating of 6 (hard endosperm is just beginning to be deposited on the germ side of the kernel) or higher is preferred by most processors, but will vary.

Possible Values 1-9; Typical Results 3-8.5

Color Rating – The Color Rating is a measurement of the color of the grain. The color of the raw material can dramatically affect product color. Individual kernels are rated by comparison to color standards. The scale for yellow corn goes from 1 (dark bronze) to 8 (bright yellow). The scale for white corn goes from 1 (light yellow) to 8 (bright white). Most processors desire ratings of 5-6 (light orange for yellow corn, or slightly off-white for white corn) or higher. Cutoffs will vary by user.
     The dark reddish-brown color is usually in the pericarp (outer kernel coat). On occasion, the endosperm may be the source of the darker orange color. During alkaline cooking, the red pigments in the pericarp react with the calcium hydroxide, turning a dark green – almost black – color. In addition, the reaction binds the dark pericarp to the endosperm. This results in poor pericarp removal index ratings and undesirable dark specks in the product.

Possible Values 1-8; Typical Results 3-7.5

Kernel Red Streaks Rating – The red streaks seen on some kernels are the same pigments that cause the overall bronze discoloration described in the Color Rating section above. Red streaking is due to a combination of genetic and environmental causes, but the dynamics are not fully understood. Some red streaks are caused by a chemical secreted by the wheat curl mite (Aceria tulipae). The streaks will often occur nearer the tip of the ear, and usually near the tip cap, although they can occur any where on the kernel. Another type of red streaks can be induced by peeling back the husks of maturing susceptible corn plants. Certain hybrids and inbreds are more susceptible than others. Some nearly always streaked, some never show streaks, and some are completely unpredictable for the occurrence of red streaks. White corn generally shows less red streaking than most yellow hybrids.
     Ratings of individual kernels are made on a scale of 1 (complete coloration of the kernel) to 8 (no red streaks). A rating of 7.8 (four out of twenty kernels may have very slight red specks) or higher is preferred by most processors, but will vary. Some processors may eliminate consideration of a sample with any red streaking.

Possible Values 1-8; Typical Results 3-8

back to IPG Corn Tests List

     Moisture Content from the Motomco 919 Moisture Meter is also offered as a component of the Basic Food Grade Test Bundle, the True Density, and Test Weight.
     Moisture content is a critical factor for the long-term storability of corn grain. Corn will reach maturity at a moisture level around 30%. Corn should be dried in the field or artificially to 15% moisture for storage up to 6 months or 13% for storage up to one year. Over-drying of corn wastes energy, money, and time. Dry corn can also negatively affect food corn processes. True Density and Test Weight will vary with moisture content, especially in corn greater than 20% moisture.
     The test involves filling the moisture meter with 250 grams of corn. A reading is obtained from the meter which correlates to a specific moisture content at the testing temperature. The moisture content is reported as an “as is”, or “wet basis”, percentage.

The ideal Moisture Content for further corn grain testing is between 12 and 16%.

Possible Values 5-40%; Typical Results 8-17%

     The Pericarp Removal Index is also offered as a component of the Alkaline Cooker Bundle.
     The alkali cooking process is used for making products such as corn tortillas, tortilla chips, and corn chips. Corn is simmered in a dilute lime (calcium hydroxide) solution. The lime dissolves the pericarp to varying degrees based on the composition of the pericarp. Water is absorbed by the kernel during cooking.
     The test involves adding samples of corn to a gently boiling 1% lime solution and simmering for 20 minutes. After the cook time is complete the sample is immediately rinsed with tap water to cease the cooking process and rinse any dissolved pericarp from the cooked grain (nixtamal). The sample is drained and stained using a dye that will color the remaining pericarp material selectively for easier rating. Individual kernel ratings are made on a scale from 1 (complete removal) to 5 (essentially no removal). Individual kernel ratings are averaged for the final reported result.

     Snack food makers would like complete removal of the pericarp. Excess pericarp in the nixtamal can lead to expensive process disruptions and also to discolored product. They prefer results of 1-3. Tortilla makers can accept more pericarp in their product. In fact, the cooked pericarp will act to help the tortilla have a longer shelf-life by retaining moisture, increasing pliability (softness) of the tortilla, and reducing the need for artificial additives. Values from 2-4 are desired.
     Some corn kernels will have a dark bronze color or red streaks in the pericarp (outer kernel coat). During alkaline cooking, the red pigments react with the calcium hydroxide, turning a dark green – almost black – color. In addition, the reaction binds the dark pericarp to the endosperm. This results in undesirable dark specks in the product.

Possible Values 1-5; Typical Results 1-4

Bad vs. Good Samples

     The Moisture Uptake Test is also offered as a component of the Alkaline Cooker Bundle.
     The Moisture Uptake Test evaluates the ability of the grain to absorb water during the alkaline cooking process. Process stability is critical to a manufacturer. Fewer adjustments to keep the process within its design parameters result in production of a more consistent product. Moisture content of the corn after cooking is a critical process parameter. The Moisture Uptake Test allows the cooking characteristics of corn samples to be compared. Processors prefer that the corn they use have consistent cooking characteristics.
     Corn samples are placed in a 1% lime (calcium hydroxide) solution at room temperature and rapidly heated to 100°C followed by 25 minutes of cooking at a gentle boil. The samples are immediately removed, cooled, and drained to remove exterior moisture. The moisture content is determined on the sample using the Air Oven method. This final moisture content after cooking is reported as the Moisture Uptake.

Possible Values 30-50%; Typical Results 35-45%

       The Grit-to-Germ Ratio is also offered as a component of the Dry Miller Bundle.
      This test relates the amount of grit (endosperm) in the kernel to the amount of germ (embryo). This is useful to all food corn users, but especially dry millers. Dry millers process the kernel to physically separate the bran (pericarp) and germ from the endosperm to produce grits. Larger grit pieces are more valuable. The germ can be processed for oil, which is also a valuable product, but incomplete separation of germ from the grit pieces greatly reduces the grit quality. Hence, the desire is for more grit and less germ in the kernel.
     In this test, kernels are soaked approximately 48 hours to soften the kernel. Twenty kernels are hand-dissected to remove the pericarp and then the germ. The germ and endosperm pieces are dried, and the percentage of the germ weight to the weight of the grit is reported on a dry basis. A lower percentage of germ is typically preferred by food corn users.

Possible Values 8.5-14.5%; Typical Results 10-12%

• Wet Milling – larger amounts of broken corn lost in cleaning (screening to remove chaff, broken grain and small kernels), lower starch yield due to high-temperature drying
• Dry Milling – larger amounts of broken corn lost to cleanout, lower yield of the most valuable products (large grits)
• Alkaline Cooking – larger amounts of broken corn lost in cleaning, disturbance of process balance leading to overcooking or undercooking

• % Stress Cracks – Percentage of kernels with at least one crack
• % Single Stress Cracks (SSC) – Percentage of kernels with only one crack
• % Double Stress Cracks (DSC) – Percentage of kernels with exactly two cracks
• % Multiple Stress Cracks (MSC) – Percentage of kernels with more than two cracks
• Stress Crack Index (SCI) – Weighted average, showing severity of cracking. SCI is calculated using the formula:

  SCI = [SSC x 1] + [DSC x 3] + [MSC x 5]

	Possible Values	Typical Results
% Stress Cracks	0-100%	0-60%
% Single Stress Cracks	0-100%	0-30%
% Double Stress Cracks	0-100%	0-20%
% Multiple Stress Cracks	0-100%	0-50%
Stress Crack Index	0-500	0-300

      On November 29, 1995, the Grain Inspection, Packers, and Stockyards Administration (GIPSA) published in the Federal Register (60 FR 61194) a final rule offering stress crack testing of corn effective January 1, 1996. The method developed at the Identity Preserved Grain Laboratory was selected as the official GIPSA method for stress crack analysis.

     The exterior integrity of the corn kernel is very important to alkaline cookers. Any nicks or cracks in the kernel will allow water to enter the kernel much faster than in an intact one. Too much water uptake during cooking can result in expensive process shutdown time or a product that does not meet specifications for quality and composition. No company can afford to have these occur at a high frequency. Some companies even pay extra premiums, over and above contracted premiums, for corn delivered above a specified level of whole kernels. While hard endosperm texture lends itself to preservation of more whole kernels than does soft corn, the primary factor in delivering whole kernels is handling during and after harvest. The type of conveyance (bucket elevators are better than screw augers), number and length of conveyances, and even combine configuration will have a profound effect on kernel integrity.
     In the Whole Kernels Test, 50 grams of cleaned (BCFM-free) corn is inspected kernel-by-kernel. Cracked, broken, or chipped grain, along with any kernels showing significant pericarp damage are removed, the whole kernels are weighed, and the result is reported as a percentage of the original 50 gram sample. Some companies perform the same test, but report the “Cracked & Broken” percentage. A Whole Kernels score of 97% equates to a Cracked & Broken rating of 3%.

Possible Values 0-100%; Typical Results 0-20%

     The Stenvert Hardness Test provides a measure of endosperm hardness to alkaline cookers and dry millers.
     The Stenvert Hardness Test measures the time-to-grind a corn sample to produce 17 ml of ground material using the Stenvert micro-hammer cutter mill fitted with a 2 mm screen. Harder corn will take longer to grind. The time required to grind the sample is reported.

Possible Values 4-25 seconds; Typical Results 5-15 seconds

     The Wisconsin Breakage Test (WBT) provides a measure of the likelihood that a sample of corn will be physically damaged, particularly by high-speed impact (such as falling from the top of a bin to the floor below) in handling. Pieces of broken corn will affect the process parameters for alkaline cookers. Dry millers will obtain more large grits and less lower-value flour from unbroken grain. Breakage susceptibility is largely influenced by endosperm hardness and Stress Cracks.
     A specialized piece of equipment is used for this test. The Wisconsin Breakage Tester uses a rapidly spinning horizontal disc to fling a sample of BCFM-free corn kernels against a vertical steel surface. The feed rate is specified at 200 grams in 20 seconds. The ensuing sample is collected from the tester and screen over a 12/64” Round Hole Screen, as is done for measuring BCFM. The percentage of material passing through the screen is reported.

Possible Values 0-30+%; Typical Results 0.5-15%

     Broken Corn & Foreign Material is part of the GIPSA Official United States Standards for Grain grading criteria. Higher levels of BCFM will indicate that a sample may have been through more, or rougher, handling than another sample with lower BCFM. Higher levels of BCFM lead to decreased storability and can be a dust explosion hazard.
     This test determines the amount of all matter that passed through a 12/64 inch round-hole sieve and all matter other than corn that remains on the top of the sieve. The IPG lab is not an officially designated grain inspection facility, and, therefore, can not issue official grades. The data from the IPG lab can be useful in making decisions, but cooperative arrangements can also be made with the local official inspection station in the case that official documentation is required. BCFM is reported as a percentage of the initial sample.

Possible Values 0-20+%; Typical Results 0-5%

     Total Damage is part of the GIPSA Official United States Standards for Grain grading criteria. This test determines the amount of damaged kernels from various reasons such as mold, insects, heat, ground, sprout, or cob rot. Most of these types of damage result in some sort of discoloration or change in kernel texture. It does not include broken pieces of grain that are otherwise normal in appearance. The IPG lab is not an officially designated grain inspection facility, and, therefore, can not issue official grades. The data from the IPG lab can be useful in making decisions, but cooperative arrangements can also be made with the local official inspection station in the case that official documentation is required.
     A representative working sample of corn is visually examined by a proper-trained individual for content of damaged kernels. Damage is reported as the weight percentage of the working sample that is damaged grain.

Possible Values 0-15+%; Typical Results 0-5%

     The Floaters, or flotation, test provides an estimate of average density of a sample, as well as the range of individual kernel densities within the sample. As with True Density, the Floaters test is a measure of endosperm hardness to alkaline cookers and dry millers.
     In the Floaters test, a solution with specific gravity (density) of exactly 1.275 grams per cubic centimeter is prepared. Externally intact kernels are placed in the solution. Harder kernels, with a density higher than 1.275, will sink. Softer kernels, with a density lower than or equal to 1.275, will float. The percentage of kernels that float is reported. The test is performed using two replicates of 100 kernels.
     This test has, to a large degree, been replaced by the True Density test due to the accuracy of the True Density test, as well as the complexity and potential hazards of preparing the Floaters test solution.

Possible Values 0-100%; Typical Results 0-100%

      NIR Proximate Analysis is also offered as a component of the Basic Food Grade Test Bundle, NIR Extractable Starch, and NIR Complete Analysis — Corn.
    Proximates are the major components of the grain. For corn, the NIR Proximate Analysis includes Oil Content, Protein Content, Starch Content (or Total Starch), and Moisture Content. The test does not include Fiber Content or Ash Content. This procedure is nondestructive to the corn. Proximate Analysis is also available using wet chemistry methods for protein content, oil content, and moisture content but the sample must be ground.
     Various end users have different demands for grain composition. A hog feeder may want increased oil and protein levels to increase feeding efficiency. A dry-grind ethanol manufacturer may want more starch, since that should increase his product yields.
     Results (other than Moisture Content) are reported on a dry basis percentage (percent of non-water material). Moisture Content is reported “as is” (percent of total sample weight).

NIR Extractable Starch provides a prediction of the yield of starch in a corn sample from the wet milling process. This procedure is nondestructive to the corn. The calibration was developed at the Agricultural and Biological Engineering Department at the University of Illinois at Urbana-Champaign using the 100 Gram Wet Milling test as the reference method.
     The primary purpose of wet milling is to efficiently separate kernel components to obtain starch. Some hybrids contain more starch than others. Differences in the grain can affect the amount of Total Starch in the corn sample that is recovered in the wet milling process as starch product. The remaining unrecovered starch goes into lower-value feed products. So, even in samples containing the same amount of Total Starch, one sample may yield considerably more starch product after milling than another.
     The starch recovery is the amount of starch product (predicted starch yield or extractable starch content) divided by the total starch present in the sample. This number can serve as a guideline to the millability, or efficiency of separation, of the sample.
     The NIR Extractable Starch test report includes the Extractable Starch Content (predicted starch yield), NIR Proximate Analysis — Corn, and the Predicted Starch Recovery. Extractable Starch is reported on a dry basis percentage.

     NIR Amino Acid Profile is also offered as a component of the NIR Complete Analysis Corn test.
     The NIR Amino Acid Profile provides an analysis of the amino acid content of a corn sample. Amino acids are the “building blocks” of protein. The proper blend of amino acids (a measure of protein quality) is necessary for a proper feed ration. Amino acids must be supplemented if the diet is insufficient or negative productivity or health consequences will develop.
     In this test, a ground sample of corn is analyzed using a NIR spectrophotometer. The instrument uses a calibration to evaluate the level of 15 individual amino acids:

     Of these, the first five — cystine, methionine, lysine, threonine, and tryptophan — are usually considered the most critical in balancing a feed ration. Amino acids are reported on a dry basis percentage. Desired levels are dependent on the end user.
     The Amino Acid Profile is also available using wet chemistry (HPLC) methods.

     NIR Fatty Acid Profile is also offered as a component of the NIR Complete Analysis Corn test.
     The NIR Fatty Acid Profile provides an analysis of the fatty acid content of a corn sample. Fatty acids are components of lipids (fats and oils). Levels of various fatty acids in livestock rations have been shown to affect animal nutrition and meat quality.
     In this test, a ground sample of corn is analyzed using a NIR spectrophotometer. The instrument uses a calibration to evaluate the level of 5 individual fatty acids:

     Fatty acids are reported on a dry basis percentage. Desired levels are dependent on the end user.
     The Fatty Acid Profile is also available using wet chemistry (Gas Chromatography) methods.