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Corn Harvest Quality Report 2015/2016

Contents

  1. Harvest Quality Highlights
  2. Introduction
  3. Quality Test Results
  4. Moisture
  5. Chemical Composition
  6. Physical Factors
  7. Mycotoxins
  8. Crop and Weather Conditions
  9. Planting and Early Growth Conditions - Spring (March - May)
  10. Pollination and Grain Fill Conditions - Summer (June - August)
  11. Harvest Conditions (September - October +)
  12. Comparison of the 2015 Average to the 2014, 2013, and 4YA
  13. Corn Production, Usage, and Outlook
  14. U.S. Corn Use and Ending Stocks
  15. Outlook
  16. Survey and Statistical Analysis Methods
  17. Survey Design and Sampling
  18. Statistical Analysis
  19. Testing Analysis Methods
  20. Corn Grading Factors
  21. Moisture
  22. Chemical Composition
  23. Physical Factors
  24. Mycotoxin Testing
  25. U.S. Corn Grades and Conversions
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D.Physical Factors

Physical factors are other quality attributes that are neither grading factors nor chemical composition. Physical factors include stress cracks, kernel weight, kernel volume and true density, percent whole kernels, and percent horneous (hard) endosperm. Tests for these physical factors provide additional information about the processing characteristics of corn for various uses, as well as corn’s storability and potential for breakage in handling. These quality attributes are influenced by the physical composition of the corn kernel, which is in turn affected by genetics and growing and handling conditions. Corn kernels are made up of four parts: the germ or embryo, the tip cap, the pericarp or outer covering, and the endosperm. The endosperm represents about 82% of the kernel, and consists of soft (also referred to as floury or opaque) endosperm and of horneous (also called hard or vitreous) endosperm, as shown to the right. The endosperm contains primarily starch and protein, the germ contains oil and some proteins, and the pericarp and tip cap are mostly fiber.

SUMMARY: PHYSICAL FACTORS

  • Average U.S. Aggregate stress cracks (3%) and stress crack index (SCI) (6.6) were lower than in 2014, 2013, and 4YA, indicating corn’s susceptibility to breakage should be less than previous years. Favorable crop growing and maturation conditions, along with good field drying and early harvest, led to less artificial drying and the very low stress cracks and SCI found in 2015.
  • Among the ECAs, the Southern Rail had the lowest SCI in 2015, 2014, 2013, and 4YA. Among all ECAs, the Southern Rail either had the lowest stress cracks or tied for lowest stress cracks in 2015, 2014, 2013, and 4YA.
  • Average U.S. Aggregate 100-k weight (34.34 g) in 2015 was higher than 2014, 2013, and 4YA.
  • Average kernel volume (0.27 cm3) for the U.S. Aggregate in 2015 was the same as 2014, 2013 and 4YA. However, the distribution indicates there was a higher percentage of large kernels in 2015 compared to the previous two years.
  • Of the ECAs, the Pacific Northwest had lowest kernel volume and 100-k weight in 2015, 2014, 2013, and 4YA.
  • Kernel true density averaged 1.254 g/cm3 for U.S. Aggregate corn in 2015, which was slightly lower than 2014, 2013, and lower than 4YA. Over the past five years, true densities have tended to be higher in years with higher protein.
  • Fewer kernels were distributed with true densities above 1.275 g/cm3, indicating slightly softer corn in 2015 than 2014 and 2013.
  • Of the ECAs, the Pacific Northwest had the lowest true density and lowest test weights in 2015, 2014, 2013, and 4YA.
  • Whole kernels averaged 94.9% for U.S. Aggregate corn in 2015, higher than 2014, 2013, and 4YA.
  • The distribution of whole kernels shows a higher percentage of whole kernels in 2015 than in 2014 and 2013. The high percentages of whole kernels and low stress crack percentages indicate the corn should handle well with minimal breakage.
  • Average U.S. Aggregate horneous endosperm (79%) was lower than 2014, 2013, and 4YA.
  • The distribution of horneous endosperm percentages indicates a lower percentage of hard endosperm samples in 2015 than in the previous two years.
  • Horneous endosperm and true density appear to change in the same direction, with higher values in a drought year such as 2012 and lower values in high-yielding years with low protein such as 2015.

1. Stress Cracks

Stress cracks are internal fissures in the horneous (hard) endosperm of a corn kernel. The pericarps (or outer covering) of stress-cracked kernels are typically not damaged, so the kernel may appear unaffected at first glance, even if stress cracks are present.

The cause of stress cracks is pressure buildup due to moisture and temperature gradients within the kernel’s horneous endosperm. This can be likened to the internal cracks that appear when an ice cube is dropped into a lukewarm beverage. The internal stresses do not build up as much in the soft, floury endosperm as in the hard, horneous endosperm; therefore, corn with a higher percentage of horneous endosperm is more susceptible to stress cracking than softer grain. A kernel may have one, two, or multiple stress cracks. High-temperature drying causing rapid moisture removal is the most common cause of stress cracks. The impact of high levels of stress cracks on various uses includes:

  • General: Increased susceptibility to breakage during handling, leading to increased broken corn which will likely need to be removed during cleaning operations for processors, and possible reduced grade/value.
  • Wet Milling: Lower starch yields because the starch and protein become more difficult to separate. Stress cracks may also alter steeping requirements.
  • Dry Milling: Lower yield of large flaking grits (the prime product of many dry milling operations).
  • Alkaline Cooking: Non-uniform water absorption leading to overcooking or undercooking, which affects the process balance.

Growing conditions will affect crop maturity, timeliness of harvest, and the need for artificial drying, which will influence the degree of stress cracking found from region to region. For example, late maturity or late harvest caused by weather-related factors such as rain-delayed planting or cool temperatures may increase the need for artificial drying, thus potentially increasing the occurrence of stress cracks.

Stress crack measurements include “stress cracks” (the percent of kernels with at least one crack) and stress crack index (SCI), which is the weighted average of single, double, and multiple stress cracks. “Stress cracks” measures only the number of kernels with stress cracks, whereas SCI shows the severity of stress cracking. For example, if half the kernels have only single stress cracks, “stress cracks” is 50% and the SCI is 50 (50 X 1). However, if all the cracks are multiple stress cracks (more than 2 cracks), indicating a higher potential for handling breakage, “stress cracks” remains at 50% but the SCI becomes 250 (50 X 5). Lower values for “stress cracks” and the SCI are always more desirable. In years with high levels of stress cracks, the SCI provides valuable information because high SCI numbers (perhaps 300 to 500) indicate the sample had a very high percentage of multiple stress cracks. Multiple stress cracks are generally more detrimental to quality changes than single stress cracks.

RESULTS

  • U.S. Aggregate stress cracks in 2015 averaged 3%, below 2014 (8%), 2013 (9%), and 4YA (6%).
  • U.S. Aggregate stress cracks standard deviation (5%) in 2015 was lower than 2014 (9%), 2013 (10%), and 4YA (7%).
  • Stress cracks ranged from 0 to 75% in 2015, whereas the ranges were from 0 to 100% in 2014 and 0 to 86% in 2013.
  • In 2015, there was a much greater percentage of samples with less than 10% stress cracks (93.2%) compared to 2014 (79%) and 2013 (80%). Also in 2015, 3.1% of the samples had stress cracks above 20%, which is fewer than in 2014 (9%) and 2013 (11%).
  • Stress crack distributions indicate the 2015 corn should have lower susceptibility to breakage than that found in 2014 and 2013.
  • Stress crack averages in 2015 were 3% for all ECAs. Among all ECAs, the Southern Rail either had the lowest stress cracks or tied for lowest stress cracks in 2015, 2014, 2013, and 4YA.
  • SCI for U.S. Aggregate corn in 2015 averaged 6.6, below 2014 (20.2), 2013 (22.8), and 4YA (14.2).
  • U.S. Aggregate SCI was less variable in 2015 (standard deviation of 11.7) compared to 2014 (27.7), 2013 (35.1), and 4YA (20.7). The 2015 SCI had a narrower range than the SCI range in 2014 and 2013.
  • Of the 2015 samples, 95.8% had SCI of less than 40, which is higher than the 89% of the 2014 samples and 86% of the 2013 samples. Only 1.8% of the 2015 samples had SCI higher than 80, compared to 7% of the 2014 samples and 9% of the 2013 samples. This distribution appears to result from 2015 having lower moisture contents at harvest and less need for artificial drying compared to 2014 and 2013.
  • SCI averages for the Gulf, Pacific Northwest, and Southern Rail ECAs were 7.0, 6.6 and 4.7, respectively.
  • The Southern Rail ECA had the lowest SCI of the ECAs in 2015, 2014, 2013, and 4YA. The lower SCI found for the Southern Rail ECA is likely related to greater field drying potential that is typically found in the states that constitute the Southern Rail ECA.
  • The high percentage of the crop having near 75% good-to-excellent crop growing conditions, along with good maturation and grain filling, early harvest conditions and favorable field drying conditions, led to less artificial drying and the very low stress cracks and SCI found in 2015.

2. 100-Kernel Weight

100-kernel (100-k) weight (reported in grams) indicates larger kernel size as 100-k weight increases. Kernel size affects drying rates. As kernel size increases, the volume-to-surface-area-ratio becomes higher, and as the ratio gets higher, drying becomes slower. In addition, large uniform-sized kernels often enable higher flaking grit yields in dry milling. Kernel weights tend to be higher for specialty varieties of corn that have high amounts of horneous (hard) endosperm.

RESULTS

  • 100-k weight for U.S. Aggregate corn in 2015 averaged 34.34 g, higher than 2014 (34.03 g), 2013 (33.41 g), and 4YA (33.77 g).
  • There was less variability in the 2015 U.S. Aggregate 100-k weights (standard deviation of 2.43 g) compared to 2014 (2.83 g), 2013 (2.88 g), and 4YA (2.78 g).
  • 100-k weight range in 2015 was 24.90 to 45.64 g and was narrower than 2014 (19.70 to 46.30 g), 2013 (18.07 to 45.09 g), and 4YA (16.59 to 46.30 g).
  • The 100-k weights in 2015 were distributed with 43.1% of the samples having 100-k weight of 35 g or greater, compared to 41% in 2014 and 39% in 2013. This distribution indicates a higher percentage of large kernels was found in 2015 than in the previous two years.
  • Average 100-k weight was lowest for the Pacific Northwest ECA (33.08 g), compared to the Gulf (34.64 g) and Southern Rail (35.09 g) ECAs. The Pacific Northwest ECA also had the lowest 100-k weight in 2014, 2013, and 4YA.

3. Kernel Volume

Kernel volume in cm3 is often indicative of growing conditions. If conditions are dry, kernels may be smaller than average. If drought hits later in the season, kernels may have lower fill. Small or round kernels are more difficult to degerm. Additionally, small kernels may lead to increased cleanout losses for processors and higher yields of fiber.

RESULTS

  • U.S. Aggregate kernel volume averaged 0.27 cm3 in 2015, which was same as 2014, 2013, and 4YA.
  • Variability was constant across the years. The standard deviation for U.S. Aggregate kernel volume was 0.02 cm3 for 2015, 2014, 2013, and 4YA.
  • Kernel volume range from maximum to minimum was less in 2015 (0.15 cm3) than in 2014 and 2013.
  • The kernel volumes in 2015 were distributed so that 85.7% of the samples had kernel volumes of 0.25 cm3 or greater, compared to 75% in 2014 and 66% in 2013. This distribution indicates there was a higher percentage of large kernels in 2015 compared to the previous two years.
  • Kernel volume for the Gulf, Pacific Northwest and Southern Rail ECAs averaged 0.28 cm3, 0.26 cm3, and 0.28 cm3, respectively. The Pacific Northwest ECA had lower average kernel volume than the other two ECAs in 2015, 2014, 2013, and 4YA.

4. Kernel True Density

Kernel true density is calculated as the weight of a 100-k sample divided by the volume, or displacement, of those 100 kernels and is reported as g/cm3. True density is a relative indicator of kernel hardness, which is useful for alkaline processors and dry millers. True density, as a relative indicator of hardness, may be affected by the genetics of the corn hybrid and the growing environment. Corn with higher density is typically less susceptible to breakage in handling than lower density corn, but it is also more at risk for the development of stress cracks if high-temperature drying is employed. True densities above 1.30 g/cm3 would indicate very hard corn desirable for dry milling and alkaline processing. True densities near the 1.275 g/cm3 level and below tend to be softer, but will process well for wet milling and feed use.

RESULTS

  • Kernel true density averaged 1.254 g/cm3 for U.S. Aggregate corn in 2015, which was lower than 2014 (1.259 g/cm3), 2013 (1.258 g/cm3), and 4YA (1.265 g/cm3).
  • There was less variability in the 2015 U.S. Aggregate of corn’s true densities (0.017 g/cm3) than in 2014 (0.020 g/cm3), 2013 (0.021 g/cm3), and 4YA (0.019 g/cm3).
  • True densities ranged from 1.166 to 1.327 g/cm3 in 2015, 1.160 to 1.340 g/cm3 in 2014, and 1.157 to 1.326 g/cm3 in 2013.
  • Only 18.7% of the 2015 samples had true densities at or above 1.275 g/cm3, compared to 30% of the samples in 2014 and 34% in 2013. Since corn with values above 1.275 g/cm3 are often considered to represent hard corn and corn with values below 1.275 g/cm3 are often considered to represent soft corn, this kernel distribution indicates softer corn in 2015 than in previous years.
  • In 2015, kernel true densities for the Gulf, Pacific Northwest and Southern Rail ECAs averaged 1.255 g/cm3, 1.249 g/cm3, and 1.255 g/cm3, respectively. Pacific Northwest average true density and test weight were lower than the other ECAs’ values in 2015, 2014, 2013 and 4YA.
  • Test weight, also known as bulk density, is based on the amount of mass that can be packed into a quart cup. While test weight is influenced by true density as shown in the adjacent figure (a correlation coefficient of 0.78), it is also affected by moisture content, pericarp damage (whole kernels), breakage and other factors. In 2015, test weight was 58.2 lb/bu, which was higher than 57.6 lb/bu and 57.9 lb/bu found in 2014 and 2013, respectively. The 2015 test weight likely remained high, in spite of low true density, due to lower moistures, high percentages of whole kernels and low breakage.

5. Whole Kernels

Though the name suggests some inverse relationship between whole kernels and BCFM, the whole kernels test conveys different information than the broken corn portion of the BCFM test. Broken corn is defined solely by the size of the material. Whole kernels, as the name implies, is the percent of fully intact kernels in the sample with no pericarp damage or kernel pieces chipped away.

The exterior integrity of the corn kernel is very important for two key reasons. First, it affects water absorption for alkaline cooking and steeping operations. Kernel nicks or pericarp cracks allow water to enter the kernel faster than intact or whole kernels. Too much water uptake during cooking can result in loss of solubles, non-uniform cooking, expensive shutdown time and/or products that do not meet specifications. Some companies pay contracted premiums for corn delivered above a specified level of whole kernels.

Second, fully intact whole kernels are less susceptible to storage molds and breakage in handling. While hard endosperm lends itself to preservation of more whole kernels than soft corn, the primary factor in delivering whole kernels is harvesting and handling. This begins with proper combine adjustment followed by the severity of kernel impacts due to conveyors and number of handlings required from the farm field to the end user. Each subsequent handling will generate additional breakage. Harvesting at higher moisture contents (e.g., greater than 25%) will usually lead to more pericarp damage to corn than harvesting at lower moisture levels.

RESULTS

  • Whole kernels averaged 94.9% for U.S. Aggregate corn in 2015, higher than 2014 (93.6%), 2013 (92.4%), and 4YA (93.5%).
  • The whole kernel standard deviation for the U.S. Aggregate corn was 2.7%, which was lower than 2014 (3.5%), 2013 (3.7%), and 4YA (3.6%).
  • Whole kernel range in 2015 (78.4 to 99.8%) was lower than 2014 (63.6 to 99.8%) and 2013 (73.6 to 99.6%).
  • Of the 2015 samples, 93.6% had 90% or higher whole kernels, compared to 86% in 2014 and 77% in 2013. This distribution indicates a higher percentage of whole kernel samples than in the previous two years.
  • Whole kernel averages for Gulf, Pacific Northwest, and Southern Rail ECAs were 95.0%, 94.8%, and 94.9%, respectively. Whole kernels were lowest for Pacific Northwest in 2015 (94.8%), 2014 (92.5%), and 4YA (93.2%).

6. Horneous (Hard) Endosperm

The horneous (hard) endosperm test measures the percent of horneous or hard endosperm out of the total endosperm in a kernel, with a potential value from 70 to 100%. The greater the amount of horneous endosperm relative to soft endosperm, the harder the corn kernel is said to be. The degree of hardness is important depending on the type of processing. Hard corn is needed to produce high yields of large flaking grits in dry milling. Mediumhigh to medium hardness is desired for alkaline cooking. Moderate to soft hardness is used for wet milling and livestock feeding.

Hardness has been correlated to breakage susceptibility, feed utilization/efficiency and starch digestibility. As a test of overall hardness, there is no good or bad value for horneous endosperm; there is only a preference by different end users for particular ranges. Many dry millers and alkaline cookers would like greater than 90% horneous endosperm, while wet millers and feeders would typically like values between 70 and 85%. However, there are certainly exceptions in user preference.

 

RESULTS

 

  • Average U.S. Aggregate horneous endosperm (79%) in 2015 was lower than 2014 and 2013 (both 82%), and 4YA (83%).
  • U.S. Aggregate standard deviation for horneous endosperm was 3%, lower than 2014, 2013, and 4YA (all 4%). The 2015 horneous endosperm range was similar to that in 2014 and 2013.
  • Of the 2015 samples, 61.4% contained less than 80% horneous endosperm, which was much higher than 38% in 2014 and 32% in 2013. This distribution indicates a lower percentage of corn samples with high proportions of hard endosperm in 2015 than in the previous two years.
  • Average horneous endosperm was uniform across the Gulf, Pacific Northwest, and Southern Rail ECAs with an average of 79% for all three ECAs.
  • The adjacent figure shows a weak but positive relationship (a correlation coefficient of 0.72) between horneous endosperm and true density for the 2015 samples.
  • The second figure shows the average U.S. Aggregate horneous endosperm and true density values over the past five years. This illustrates that average U.S. Aggregate horneous endosperm is higher in years when average U.S. Aggregate true density is higher.