Home

Corn Harvest Quality Report 2012/2013

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 (August-October +)
  12. U.S. Corn Production, Usage, Outlook
  13. U.S. Corn Use and Ending Stocks
  14. Outlook
  15. Survey and Statistical Analysis Methods
  16. Survey Design and Sampling
  17. Statistical Analysis
  18. Testing Analysis Methods
  19. Corn Grading Factors
  20. Moisture
  21. Chemical Composition
  22. Physical Factors
  23. Mycotoxin Testing
Download report

D.Physical Factors

Physical factors are other quality attributes that are neither grading factors nor chemical composition. Tests for physical factors provide additional information about the processing performance of corn for various uses, as well as its storability and potential for breakage in handling. The storability, the ability to withstand handling, and the processing performance of corn are influenced by corn’s morphology or parts. 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. The following tests reflect these intrinsic parts of the corn kernels, in addition to the growing and handling conditions that affect corn quality.

1. Stress Cracks

Stress cracks are internal fssures in the horneous (hard) endosperm of a corn kernel. The pericarp of a stress-cracked kernel is typically not damaged, so the outward appearance of the kernel may appear unaffected at first glance if stress cracks are present. The cause of stress cracks is pressure buildup due to large moisture gradients 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 cannot build up as much in the soft, floury endosperm as in the horneous endosperm; therefore, corn with a higher percent of horneous endosperm is more susceptible to stress cracking than softer grain with a lower percent of horneous endosperm. A kernel may have one, two, or multiple cracks. High-temperature drying 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 needing to be removed during cleaning operations for processors, and possible reduced grade/value.
  • Wet Milling: Lower starch yield because the starch and protein are 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 greatly affect the need for artificial drying and will influence the degree of stress cracking found from region to region. For example, late maturity or late harvest caused by weatherrelated 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 measure only the number of kernels with stress cracks whereas SCI shows the severity of cracking. For example, if half the kernels have only single stress cracks, stress cracks are 50% and the SCI is 50. However, if all the cracks are multiple stress cracks, indicating a higher potential for handling issues, stress cracks remain at 50% but the SCI becomes 250. Lower values for stress cracks and the SCI are always better. In years with high levels of stress cracks, the SCI is valuable because high SCI numbers (perhaps 300 to 500) indicate the sample had a very high percent of multiple stress cracks. Multiple stress cracks are somewhat more detrimental to quality changes than single stress cracks.

HIGHLIGHTS

  • Stress cracks of U.S Aggregate corn averaged 4% in 2012 (3% in 2011).
  • Stress cracks ranged from 0 to 63% with a standard deviation of 5% (3% in 2011).
  • Stress cracks distribution showed 90.8% (96.2% in 2011) of samples with less than 10% stress cracks.
  • The percent of stress cracks for all regions including the Gulf, Pacific Northwest and Southern Rail ECAs was extremely low averaging only 3 to 4%.
  • SCI had a low U.S. Aggregate average of 9.3 (4.6 in 2011) with a range of 0 to 217.
  • 95.8% of the samples had an SCI of less than 40, indicating very few kernels had double or multiple stress cracks. This is the normal expectation at the first point of delivery.
  • The low levels of stress cracks observed should result in reduced rates of breakage when corn is handled, improved wet milling starch recovery, improved dry milling yields of flaking grits, and good alkaline processing performance.

2. 100-Kernel Weight

100-kernel (100-k) weight indicates larger kernel size as 100-k weights increase. Large kernels affect drying rates and large uniform-sized kernels often enable higher flaking grit yields in dry milling. Kernel weights tend to be higher for varieties with high amounts of horneous (hard) endosperm.

HIGHLIGHTS

  • 100-k weights of U.S. Aggregate corn averaged 34.53 g in 2012, compared to 33.11 g in 2011.
  • 100-k weights ranged from 17.49 to 45.39 g. This shows a wide range of kernel sizes was found across all ECAs.
  • The 100-k weights were distributed so that 87.4% of the aggregate samples had 100-k weights of 30 g or greater.

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 loss for processors and higher yields of fiber.

HIGHLIGHTS

  • Kernel volume averaged 0.27 cm3 for U.S. Aggregate corn in 2012 which was higher than expected for drought-year corn and even higher than 2011 corn. Kernel volumes ranged from 0.14 to 0.35 cm3. The higher kernel volumes in 2012 are consistent with the higher 100-k weights which also indicate larger kernels sizes in 2012 than in 2011.
  • There was no difference in average kernel volume among ECAs.

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. 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.

HIGHLIGHTS

  • Kernel true density averaged 1.276 g/cm3 for U.S. Aggregate corn in 2012 which is significantly higher than 1.267 g/cm3 found in 2011. In 2012, true densities ranged from 1.199 to 1.332 g/cm3.
  • Since moistures of samples when tested for true density in 2012 averaged 0.3% points lower than in 2011, a comparison was made for both years after kernel true densities were adjusted to 15.0% moisture. After adjustment to constant moisture, true densities in 2012 averaged 1.271 g/cm3 and they would have averaged 1.263 g/cm3 in 2011. Either way, with or without moisture adjustment, the 2012 U.S. Aggregate samples remained 0.009 g/cm3 higher in density than the samples in 2011.
  • Kernel true densities were distributed so that more than 52.3% of the samples were at or over 1.275 g/cm3 in 2012 compared to only 40.8% of the samples that high in 2011. This would indicate kernels in 2012 tend to have harder endosperm. The harder endosperm and higher true densities in 2012 were consistent with the higher test weights also found in 2012.
  • Kernel true density was relatively constant among ECAs (averages between 1.275 to 1.277 g/cm3).

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.

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

Second, an intact whole kernel is important for all corn that has to be stored or handled. Fully intact whole kernels are less susceptible to storage molds and breakage in handling. While hard endosperm texture lends itself to preservation of more whole kernels than soft corn, the primary factor in delivering whole kernels is handling during and after harvest. This begins with the combine configuration followed by the type, number and length of conveyance required to go from the farm to end user. All subsequent handling will generate additional breakage to some degree. Harvesting at higher moisture contents (e.g., greater that 25%) will usually lead to more damage to grain than harvesting at lower moisture levels (less than 18%).

HIGHLIGHTS

  • Percent of whole kernels averaged 94.4% for U.S. Aggregate corn compared to 93.8% in 2011. In 2012, whole kernels ranged from 68.0 to 100.0%.
  • 89.5% of the U.S. Aggregate samples had whole kernels equal to or greater than 90%.
  • Percent of whole kernel averages for Gulf, Pacific Northwest, and Southern Rail were 94.4%, 94.1%, and 94.7%, respectively.
  • Percent of whole kernels was high when farm corn was delivered to local elevators. The high initial percent of whole kernels should reduce storage risk and in combination with the low stress cracks should enable reduced breakage in handling.

6. Horneous Endosperm

The horneous endosperm test measures the percent of horneous or hard endosperm 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. Medium-high 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.

HIGHLIGHTS

  • Horneous endosperm averaged 85% for U.S. Aggregate corn in 2012 compared to 84% in 2011.
  • Horneous endosperm ranged from 74 to 97% in 2012 compared to 71 to 95% in 2011. Thus, the higher percentages of hard endosperm found in 2012 are consistent with the higher levels of true density, indicating harder corn in 2012.
  • Of the U.S. Aggregate samples, 86.7% resulted in equal to or greater than 80% horneous endosperm in 2012, compared to only 78.9% in 2011.
  • Horneous endosperm percentages did not vary substantially across ECAs (averages were 85 to 86%).

SUMMARY: PHYSICAL FACTORS

  • The low levels of stress cracks (4%) should result in a high probability of reduced rates of breakage when corn is handled, improved wet milling starch recovery, improved dry milling yields of flaking grits, and good alkaline processing characteristics. These, however, may be affected by further drying and handling in the marketing channel.
  • In spite of a drought year, average kernel volumes and 100-k weights were significantly higher in 2012 than in 2011.
  • Kernel true densities were significantly higher in 2012 than in 2011. Similarly, hard endosperm percentages were higher in 2012 than in 2011 indicating a greater prevalence of hard endosperm corn in 2012. The average true density of 1.276 g/cm3 and the higher kernel volumes should indicate good availability of corn for dry milling and alkaline processing uses, yet it should still be acceptable for wet milling and feeding.
  • The relatively high initial whole kernels (94.4%) in combination with the low stress cracks (4%) provide an indication of good storable corn that should also have reduced breakage in handling.