III. QUALITY TEST RESULTS
A. Grade Factors
The U.S. Department of Agriculture’s Federal Grain Inspection Service (FGIS) has established numerical grades, definitions and standards for measurement of many quality attributes. The attributes which determine the numerical grades are test weight, broken corn and foreign material (BCFM), total damage, and heat damage. The corn grades and grade requirements are summarized in the “U.S. Corn Grades and Conversions” section on page 47.
1. Test Weight
Test weight (weight per volume) is a measure of bulk density and is often used as a general indicator of overall quality and as a gauge of endosperm hardness for alkaline cookers and dry millers. High test weight corn will take up less storage space than the same weight of corn with a lower test weight. Test weight is initially impacted by genetic differences in the structure of the kernel. However, it is also affected by moisture content, method of drying, physical damage to the kernel (broken kernels and scuffed surfaces), foreign material in the sample, kernel size, stress during the growing season, and microbiological damage. When sampled and measured at the point of delivery from the farm at a given moisture content, high test weight generally indicates high quality, high percent of horneous (or hard) endosperm and sound, clean corn. Test weight is highly correlated with true density and reflects kernel hardness and kernel maturity.
- The U.S. Aggregate average test weight in 2013 was 57.9 lb/bu (74.5 kg/hl), compared to 58.8 lb/bu (75.6 kg/hl) in 2012 and 58.1 lb/bu (74.8 kg/hl) in 2011.
- Average test weight for each ECA was also above the grade limit for U.S. No. 1. The Gulf and Southern Rail ECAs had the highest test weights, 58.1 lb/bu and 58.3 lb/bu, respectively.
- Sample values were less uniform in the 2013 crop relative to 2012, as indicated by the higher standard deviation. Standard deviations for 2013, 2012 and 2011 were 1.51 lb/bu, 1.21 lb/ bu and 1.49 lb/bu, respectively.
- Test weight values were distributed with 81.5% of the samples at or above the factor limit for U.S No. 1 (56 lb/bu) and 94.0% at or above the No. 2 grade limit of 54 lb/bu.
- Test weight was highest in the Southern Rail ECA (58.3 lb/bu) and the lowest in the Pacific Northwest ECA (56.5 lb/bu).
2. Broken Corn and Foreign Material (BCFM)
Broken corn and foreign material (BCFM) is an indicator of the amount of clean, sound corn available for feed and processing. The lower the percentage of BCFM, the less foreign material and/or fewer broken kernels are in a sample. Higher levels of BCFM in farm-originated samples generally stem from combine settings and/or weed seeds in the field. BCFM levels will normally increase during drying and handling, depending on the methods used and the soundness of the kernels. Increased stress cracks at harvest will also result in an increase in broken kernels and BCFM during subsequent handling.
Broken corn is defined as everything small enough to pass through a 12/64th inch round-hole sieve, but too large to pass through a 6/64th inch round-hole sieve.
Foreign material is defined as any non-corn material too large to pass through a 12/64th inch round-hole sieve, in addition to all fine material small enough to pass through a 6/64th inch round-hole sieve.
- Average BCFM for the U.S. Aggregate (0.9%) was slightly higher than in 2012 (0.8%) but lower than in 2011 (1.0%).
- The 2013 crop was more uniform in BCFM than the 2011 crop, but less uniform than the 2012 crop. The BCFM U.S. Aggregate values ranged from 0.1 to 5.8% with a standard deviation of 0.61% in 2013, compared to 0.53% in 2012 and 0.65% in 2011.
- BCFM in the Pacific Northwest ECA was slightly higher (1.1%) than the U.S. Aggregate and the other two ECAs.
- BCFM U.S. Aggregate values were distributed with 92.6% of the samples containing 2% or less.
3. Broken Corn
Broken corn in U.S. grades is based on particle size and usually includes a small percent of non-corn material. Broken corn is more subject to mold and insect damage than whole kernels, and it can cause problems in handling and processing. When not spread or stirred in a storage bin, broken corn tends to stay in the center of the bin while whole kernels are likely to gravitate outward to the edges. The center area in which broken corn tends to accumulate is known as a spoutline. If desired, the spoutline can be reduced by drawing grain out of the center of the bin.
- Broken corn in the U.S. Aggregate samples averaged 0.7% in the 2013 crop, very close to the levels in 2012 and 2011 crops.
- Broken corn average value in the Pacific Northwest ECA was slightly higher than those in the other two ECAs (0.8% compared to 0.7% in the other two ECAs).
- The 2013 crop was more uniform than the 2011 crop, but less uniform than the 2012 crop. The standard deviation in the 2013 crop was 0.46% compared to 0.42% in 2012 and 0.52% in 2011. However, the range in values in 2013 was smaller than in 2012 and 2011, ranging from 0.1 to 3.9%, 0 to 4.8%, and 0 to 10.1%, respectively.
- U. S. Aggregate values for the 2013 samples were distributed with 39.0% of the samples less than 0.5% and 80.1% less than 1.0% broken corn.
- The distribution chart to the right, displaying broken corn as a percent of BCFM, shows that in nearly all samples, BCFM consisted primarily of broken corn, as was found in previous years.
4. Foreign Material
Foreign material is of importance because it has little feed or processing value, is generally higher in moisture content than the corn and therefore creates a potential for deterioration of corn quality during storage. Foreign material also contributes to the spoutline and has the potential for creating more quality problems than broken corn because of the higher moisture level as mentioned above.
- Foreign material in the U.S. Aggregate samples averaged 0.2% in 2013, the same as in 2012 and 2011.
- In the 2013 crop, 91.5% of the samples contained less than 0.5% foreign material.
- Variability among the U.S. Aggregate samples in 2013 was slightly higher than in 2012 with a standard deviation of 0.23% compared to 0.18% in 2012 and 0.20% in 2011.
- All ECAs had average foreign material values equal to or less than 0.3%, differing little from the 2011 crop.
5. Total Damage
Total damage is the percentage of kernels and pieces of kernels that are visually damaged in some way, including damage from heat, frost, insects, sprouting, disease, weather, ground, germ, and mold. Most of these types of damage result in some sort of discoloration or change in kernel texture. Damage does not include broken pieces of grain that are otherwise normal in appearance.
Mold damage is usually associated with higher moisture content and high temperature in growing and/or storage. Mold damage and the associated potential for mycotoxins is the damage factor of greatest concern. Mold damage can occur prior to harvest as well as during temporary storage at high moisture and high temperature levels before delivery.
- Total damage in the U.S. Aggregate samples averaged 0.9% in 2013, compared to 0.8% in 2012 and 1.1% in 2011.
- Total damage in the U.S. Aggregate samples ranged from 0.0% to 13.6%, a higher range than in either of the two previous years.
- The few samples with high damage levels in 2013 (13.6% for example) were associated with a high moisture content when delivered to the elevator.
- Total damage in the U.S. Aggregate samples was distributed with 95.7% of the samples having 3% or less damaged kernels, and 99.0% having 5% or less.
- Total damage average values were lowest in the Pacific Northwest ECA (0.6%) compared to the Gulf and Southern Rail ECAs (0.9% and 1.0%, respectively).
- Average total damage values in all ECAs were well below the limit for U.S. No. 1 corn (3.0%) indicating that total damage was not a problem in farm deliveries.
6. Heat Damage
Heat damage is a subset of total damage and has separate allowances in the U.S. Grade standards. Heat damage can be caused by microbiological activity in warm, moist grain or by high heat applied during drying. Heat damage is seldom present in corn delivered at harvest directly from farms.
- There was no heat damage reported in any of the samples, the same results as in 2012 and 2011.
- The absence of heat damage likely was due in part to fresh samples coming directly from farm to elevator with minimal prior drying.