Grain Grading standards in feed manufacturing
April 01, 1999
by Teresa Acklin
Use of low-grade grain may increase profits but could affect processing performance and feeding value.
By Tim Herman and Gerry Kuhl
In 1916, a system of grain grading stan- dards was developed in the United States to enable grain merchants to trade grain using consistent, measurable quality criteria. In the years since, these grading standards have changed often to reflect changes in technology and customer demands.
The most current standards, the Grain Grading Standards established by the U.S. Department of Agriculture in 1995, serve as a general guideline for characterizing physical grain quality. But grain grades also provide valuable information to the end user regarding feed processing performance and feeding value of low-grade grain.
Each year some low-quality grain enters the market following a growing season characterized by drought, extreme heat during a sensitive stage in crop development, excessive moisture, an early frost, plant disease or other maladies.
During years when vast geographical areas are affected by unfavorable growing conditions, a large quantity of low-grade grain may be available at a substantial discount. Feed manufacturers must factor into their purchasing decision the cause of grain quality deterioration, increased cost of processing and potential health risks to the animal. A thorough understanding of the Grain Grading Standards will enable feed manufacturers to make wise choices regarding the purchase and use of low-grade grain.
Grain quality measurements are categorized as nongrade determining factors, grade determining factors and special grades. Each commodity has a set of grades and grade requirements that list the minimum and maximum criteria for each grading factor and the definition of each special grade (see table on Page 38). These characteristics provide some insight into the processing value, past or future problems related to storage and, to a lesser extent, the nutritional value of grain.
The Federal Grain Inspection Service and licensed inspection agencies and companies also offer informational services and tests to measure quality characteristics, including mycotoxins, protein and oil content and stress crack in corn.
NONGRADE DETERMINING FACTORS.
These factors, which include moisture and possibly dockage, are measured using approved testing equipment following official procedures. The results of these tests are included on the grade certificate but are not used to assign a grade.
For example, an individual purchasing U.S. No. 2 corn (maize) may receive grain with any moisture content (such as 10% to 20%).
Moisture content was dropped as a grade determining factor in 1988 as an outgrowth of the Grain Standards Act of 1986. Because moisture level in grain is extremely important, it is measured and reported on all grade certificates.
Moisture content is important for several reasons, primarily because it indicates how much dry matter (feeding value) is contained in the grain. A reduction in moisture content in grain results in a weight reduction is referred to as “shrink.” This moisture-to-weight relationship is expressed by the following equation:
% weight change (shrink) = Mo/ 100 - Mf / Mf x 100
Mo = original or initial moisture content (%)
Mf = final moisture content (%)
The percent weight change or moisture shrink when corn dries from 17% to 14% can be calculated as follows:
% weight change (shrink) = 17/100 - 14/14 x 100 = 3.49
A shrink factor can be derived by dividing moisture shrink by the percent change in moisture content: 3.49 ¸ 3 = 1.16. Many grain elevators use a fixed moisture shrink factor (in this case, 1.2) when discounting high-moisture grain to a predetermined moisture content.
Moisture content in grain also determines the length of time grain can be stored. High moisture grain is more prone to experience a deterioration in quality due to mold. The relationship between grain moisture content and quality deterioration due to mold is dependent on temperature (see table below). The presence of mold can result in reduced grain palatability, feed refusal and the occurrence of mycotoxins, which are toxic metabolites that can cause severe animal health problems and death.
Grain moisture content also has an inverse relationship with test weight. As moisture content increases, test weight decreases (see chart on Page 37).
Dockage in feed grain is measured for barley, rye, sorghum, triticale and wheat, and is removed prior to measuring test weight for all grains except sorghum.
Dockage is defined in the U.S. Wheat Standards as the nonwheat material removed by an approved cleaning device. The Carter Day dockage tester is the approved cleaning device for official inspection in the U.S., although other grain cleaners are available for measuring dockage. In the absence of a mechanized method for removing dockage, hand sieves may be used.
Dockage may posses limited feeding value and hinders airflow through stored grain, which results in uneven cooling and development of hot spots. Dockage slows the grain flow through the pit, reduces leg capacity and lowers the test weight measure of grain.
GRADE DETERMINING FACTORS.
Factors such as test weight, damaged kernels, foreign materials, broken kernels, odor, heating and other materials found in grain are used to assign a numerical grade. Grades are assigned based on the lowest factor.
If a corn sample has a test weight of 56 lbs per bu (the mimimum criteria for U.S. No. 1 corn) and heat damage of 1% (maximum criteria for U.S. No. 4), the grade assigned to the grain would be U.S. No. 4. The presence of musty, sour or commercially objectionable foreign odor or the presence of heating causes the grain to be assigned a sample grade, which is the lowest possible category in the grading system.
Test weight is a bulk density measure (weight per given volume) and is reported as pounds per Winchester bushel (bu). While low test weight may not translate into reduced feeding value, processing costs may increase dramatically.
Data generated at Kansas State University from 1991 to 1994 for swine indicated that the feeding value of sorghum with a test weight as low as 35 lbs per bu was only 10% to 12% lower than that of 57 lbs per bu. This reduction in feeding value of light sorghum is in sharp contrast with the 30% to 50% discount in price received by farmers.
However, when comparing processing performance of high and low test weight sorghum, K.S.U. researchers report that as test weight dropped from 58 lbs to 39 lbs per bu, grinding rate was reduced by 45% and grinding cost increased fivefold from U.S. 41c per ton to U.S.$2.33 per ton.
Many other studies evaluating the feeding value of low test weight grains on different animal species indicate that there is little or no correlation between test weight and animal performance. Perhaps the only contradiction was reported for barley in Idaho when researchers discovered in a cattle finishing study that average daily gain and feed efficiency fell about 1% for each pound decrease in test weight.
Foreign material is the nongrain material that remains in a sample after the dockage is removed.
Dockage is not measured in grains and oilseeds such as corn and soybeans, so foreign material takes on a slightly different meaning. In corn, the foreign material is measured with broken corn and is defined as all matter that passes readily through a 12/64-inch round hole sieve and all matter other than corn that remains in the sieved sample.
Broken corn and foreign material (BCFM) generally elevates the fiber content while protein and nitrogen free extract content is usually comparable to clean grain. Although BCFM provides limited information pertaining to the nutritional value of corn, this grading factor does indicate possible handling, storage and processing problems. Broken kernels are more susceptible to mold invasion and insect infestation during storage. BCFM limits air flow in storage and contributes to feedbunk fines.
Damaged kernels can include evidence of heat damage, germ damage, sprouting, mold and insect damage.
Heat damage is designated separately in all grading charts and represents the tightest standard for kernel damage. Kernels experiencing heat damage tend to possess limited nutritional value.
Heat damage results from storing grain that possessed too high of a field moisture content, from moisture migration due to convective air currents in the bin or from localized infestations of stored grain insects that produce heat. Any of these conditions creates an environment that favors mold growth and heating from respiration. As a consequence, the endosperm turns dark brown or black.
Drier damage may result in kernels that are puffed or swollen and materially discolored by the drier heat. This form of damage, if of similar intensity as heat damage, may be designated as such. Grain damage caused by a drier that appears less severe than heat damage is designated as damaged by heat.
Germ damage is caused by heat of respiration, although only the embryo (germ) is damaged. This form of damage in corn would result in off-color oil. Since the severity of damage is less than heat damage, there is little or no effect on the nutritional value or feed processing characteristics.
Sprout damage occurs in the field when physiologically mature grain is exposed to rain and high humidity and may occur in storage in response to conditions described under heat damage.
Sprouting is caused by an activation of enzymes that convert the long-chain starch molecules in the endosperm into smaller carbohydrates and simple sugars, which serve as food to the young plant. Storage proteins also are split into smaller compounds during sprouting. The feeding value of sprout-damaged grain is not affected.
The occurrence of sprout-damaged grain may indicate other problems, such as the presence of molds and my-cotoxins.
Mold damage may occur during the growing season or in storage. Grain stored under high moisture or temperature conditions is more prone to mold problems and the development of my-cotoxins.
Scab damage in wheat results from field infection by Fusarium species during flowering and kernel development. Kernels that are scab damaged have a dull, lifeless, chalky appearance and usually contain mold in the germ or in the crease.
Scabby wheat may contain deoxy-nivalenol (DON), also called vomitoxin. Symptoms of DON-contaminated wheat include feed refusal, digestive disorders, diarrhea and possibly death.
The presence of odor or heating causes grain to be designated as sample grade, which is the lowest designation in the grain grading system. Odors are indicative of a grain storage or transportation problem.
Musty odor indicates the presence of certain grain boring insects or mold. Commercially objectionable foreign odor may result from petroleum products or excessive fumigant use. Sour odor may be an indication of insect infestation or fermenting or moldy grain.
Rodent excrement also may cause an off odor. Rodents, cats and birds can potentially spread disease through feces, urine and body parts such as feathers or hair. Grain should be thoroughly inspected for the cause of odor.
Special grades include infested, ergoty, garlicky and smutty grains. These words are added to the grain designation but do not determine the numerical grade.
Sorghum that meets or exceeds grading factors for U.S. No. 1 and contains 20 or more smut balls in a 100-gram portion would be assigned the following grade: U.S. No. 1 Sorghum, Smutty.
Infested grain, while possibly possessing satisfactory feeding value and processing performance, can lead to economic losses. Many grain elevator managers discount grain by U.S.5c per bu to cover the cost of fumigating infested grain.
Feed manufacturers should not knowingly receive infested grain without a discount and fumigation strategy in place. The use of fumigants requires personnel with a special applicators permit and proper equipment.
Ergot may occur in cultivated grasses, including wheat, triticale, barley, oats and rye. A purple-black fungal mass (sclerotium) contains alkaloids that can cause gangrene or convulsions.
Smutty grain may produce an off odor but is potentially not a threat to the nutritional value of grain or to animal health. Most smut problems can be controlled during production through the use of a fungicide seed treatment.
Tim Hermann is Extension State Leader in the Department of Grain Science and Industry and Industry at Kansas State University, Manhattan; Gerry Kuhl is Extension Feedlot Specialist in the Department of Animal Sciences and Industry at K-State.
Maximum time (days) for storage of shelledWheat grades and grade requirements
corn at various moisture contents and air
temperatures to experience one grade reduction
temperature Corn moisture content
(°F) 15% 20% 25% 30%
75 116 12 4 3
70 155 16 5 4
65 207 21 8 5
60 259 27 10 6
55 337 35 13 8
50 466 48 17 10
45 725 75 27 16
40 906 94 34 20
35 1140 118 42 25
Source: David Sauer, “Stored Grain Management,”
Kansas State University, Manhattan, 1988.
|Minimum limits of:|| ||Maximum limits of:|
|Wheat of |
|Test weight||Defects||other classes1 ||Other material|
|(lbs/bu) ||(percent)||(percent) ||(count)|
| ||or white||sub-||kernals||aged||mat-||bro-||classes||fifth||seeds||foreign|
| ||club||classes||kernals ||erial||ken||material|
|U.S. No.1 ||58.0||60.0||2.0||0.2||0.4||3.0||3.0||1.0||3.0||1||1||2||0||3||3||4|
|U.S. Sample||(a) Does not meet the requirements for U.S. Nos. 1, 2, 3, 4 or 5;|
|(b) Has a musty, sour or commercially objectionable foreign odor (except for smut or garlic odor); or|
|(c) Is heating or of distinctly low quality.|
| Special grades ||(a) Ergoty wheat: Wheat that contains more than 0.05% of ergot;|
|(b) Garlicky wheat: Wheat that contains in a 1,000-gram portion more than two green garlic bulblets or an|
| equivalent quantity of dry or partly dry bulblets;|
|(c) Infested wheat: Wheat that is infested with two or more live insects injurious to stored grain;|
|(d) Light smutty wheat: Wheat that has an unmistakable odor of smut or which contains, in a 250-gram|
|portion, smut balls, portions of smut balls or spores of smut in excess of a quantity equal to five smut balls, |
|but not in excess of a quantity equal to 30 smut balls of average size;|
|(e) Smutty wheat: Wheat that contains in a 250-gram portion, smut balls, portions of smut balls or spores of|
| smut in excess of a quantity equal to 30 smut balls of average size;|
|(f) Treated wheat: Wheat that has been scoured, limed, washed, sulfured or treated in such a manner that|
| the true quality is not reflected by either the numerical grades or the U.S. Sample grade designation alone.|
|1Unclassed wheat of any grade may contain not more than 10% of wheat of other classes.|