Home

Corn Export Cargo Quality Report 2015/2016

Contents

  1. Export Cargo Quality Highlights
  2. Introduction
  3. Quality Test Results
  4. Moisture
  5. Chemical Composition
  6. Physical Factors
  7. Mycotoxins
  8. U.S. Corn Export System
  9. U.S. Corn Export Flow
  10. Impact of the Corn Market Channel on Quality
  11. U.S. Government Inspection and Grading
  12. Survey and Statistical Analysis Methods
  13. Survey Design and Sampling
  14. Statistical Analysis
  15. Testing Analysis Methods
  16. Corn Grading Factors
  17. Moisture
  18. Chemical Composition
  19. Physical Factors
  20. Mycotoxin Testing
  21. U.S. Corn Grades and Conversions
Download report

D. Physical Factors

Physical factors are other quality attributes that are neither grading factors nor chemical composition. Physical factors include stress cracks, kernel weight, volume and 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, as well as 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 above. 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 (6%) was lower than 2014/2015 (14%) and 4YA (12%). The low stress cracks percentage in 2015/2016 was likely a result of good field drying conditions and softer endosperm corn. The majority of the export samples (96.8%) had less than 15% stress cracks, and should have low rates of breakage during handling.
  • At export, only 20.3% had SCI of 20 or higher, indicating fewer kernels in 2015/2016 had double or multiple stress cracks than in 2014/2015.
  • Average U.S. Aggregate 100-kernel (100-k) weight was lower than 2014/2015 and 4YA, indicating smaller kernel sizes in 2015/2016 corn exports than in the previous year.
  • Average kernel volumes at export and at harvest were essentially the same (0.27 cm3) in 2015/2016 and 4YA.
  • Average 100-k weight and kernel volume were lower for the Pacific Northwest ECA than for the other ECAs for 2015/2016, 2014/2015, 2013/2014, and 4YA, indicating smaller kernel sizes over time for the Pacific Northwest ECA than for the other ECAs.
  • Average U.S. Aggregate true density (1.275 g/cm3) was lower than 2014/2015 (1.295 g/cm3) and 4YA (1.292 g/cm3).
  • Average U.S. Aggregate true densities, test weights, and kernel volume were lower for 2015/2016 than for 2014/2015.
  • The average percentage of whole kernels at export (89.5%) was higher than 2014/2015 (88.4%) and 4YA (88.6%).
  • Average U.S. Aggregate horneous endosperm (80%) was lower than 2014/2015 (82%) and 4YA (83%). The true density and horneous endosperm test results indicate the 2015/2016 corn will be softer than in previous years.
  • Horneous endosperm at export in 2015/2016 and the previous two years was within ±1% of the average horneous endosperm percentage at harvest.

1. Stress Cracks and Stress Crack Index (SCI)

Stress cracks are internal fissures in the horneous (hard) endosperm of a corn kernel. The pericarp (or outer covering) of a stress-cracked kernel is 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 differences 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 horneous endosperm; therefore, corn with higher percentages of horneous endosperm is more susceptible to stress cracking than softer grain. A kernel may vary in severity of stress cracking and can have one, two or multiple stress cracks. The impact of high levels of stress cracks on various uses include:

  • 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.

High-temperature drying is the most common cause of stress cracks. 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. Then, as corn moves through the market channel, some stress-cracked kernels break, which increases the proportion of broken corn. Concurrently, impacts of kernels on other kernels or on metal surfaces during handling may cause new cracks in kernels. As a result, the percentage of kernels with stress cracks may not remain constant throughout the merchandising channel.

Stress crack measurements include “stress cracks” (the percentage 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 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 half the kernels have multiple stress cracks (more than two cracks), indicating a higher potential for handling issues, “stress cracks” remain 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 is particularly relevant because high SCI values (perhaps 300 to 500) indicate the sample had a very high percentage of multiple stress cracks. Kernels with multiple stress cracks are more susceptible to breakage during subsequent handling.

RESULTS: STRESS CRACKS

  • Average U.S. Aggregate stress cracks (6%) were lower than 2014/2015 (14%) and 4YA (12%). The low stress cracks in 2015/2016 may be due to less heated-air drying and a greater prevalence of soft endosperm corn.
  • Average U.S. Aggregate stress cracks (6%) was higher than for the 2015 harvest samples (3%).
  • Stress cracks in the export samples (with a range of 0 to 26% and a standard deviation of 4%) were more uniform than the 2015 harvest samples (with a range of 0 to 75% and a standard deviation of 5%).
  • Of the 2015/2016 export samples, 96.8% had less than 15% stress cracks, compared to 60% in 2014/2015. Samples with less than 15% stress cracks should have relatively low rates of breakage during handling.
  • Stress cracks averages were 5%, 7%, and 5% for the Gulf, Pacific Northwest, and Southern Rail ECAs, respectively. The variability of stress cracks (standard deviation) was nearly the same (4 to 6%) across all ECAs.
  • Stress cracks for contracts loaded as U.S. No. 2 o/b (6%) were the same as those for contracts loaded as U.S. No. 3 o/b (6%).

RESULTS: STRESS CRACK INDEX (SCI)

  • Average U.S. Aggregate stress crack index (SCI) (12.1) was lower than 2014/2015 (33.3) and 4YA (34.0).
  • SCI ranged from 0 to 64, with a standard deviation of 10.7.
  • SCI at export was higher than the SCI found at harvest (6.6).
  • Average SCI for the Gulf ECA (11.3) was lower than the average SCI for the Pacific Northwest (14.7) and Southern Rail (12.0) ECAs.
  • SCI standard deviations across ECAs were 9.7, 10.9, and 14.9 for the Gulf, Pacific Northwest, and Southern Rail ECAs, respectively.
  • At export, 20.3% of the samples had SCI of 20 or higher, compared to 72% of the 2014/2015 samples having a SCI of 20 or higher. This would indicate fewer kernels had double or multiple stress cracks in 2015/2016 than in 2014/2015.
  • SCI for contracts loaded as U.S. No. 2 o/b (12.6) was lower than contracts loaded as U.S. No. 3 o/b (14.1).

2. 100-Kernel Weight

100-kernel (100-k) weight (reported in grams) indicates larger kernel size as 100-k weights increase. Kernel size affects drying rates. As kernel size increases, the volume-to-surface area ratio becomes higher, and as this 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

  • Average U.S. Aggregate 100-k weight (34.73 g) was lower than 2014/2015 (36.08 g) and 4YA (35.51 g).
  • The 100-k weight values for the 2015/2016 samples ranged from 28.95 to 40.55 g.
  • 100-k weight was higher at export than for the 2015 harvest corn (34.34 g). Higher average 100-k weight at export than at harvest has occurred for the past two years and 4YA. Since the 100-k weights are based on 100 fully intact kernels, any breakage occurring in transit could have self-selected out smaller kernels that might have been soft or more prone to breakage.
  • The 2015/2016 export samples had a lower standard deviation (1.62 g) than the 2015 harvest samples (2.43 g), indicating greater uniformity at export.
  • The average 100-k weight was lowest for the Pacific Northwest ECA (32.02 g) in comparison to the Gulf (35.24 g) and Southern Rail (36.39 g) ECAs. The Pacific Northwest ECA had the lowest average 100-k weight of the three ECAs in the previous two years and for 4YA.
  • Of the 2015/2016 export samples, 78.4% had 100-k weight of less than 36.5 g, compared to 48% of the 2014/2015 and 57% of the 2013/2014 samples, indicating smaller kernels in 2015/2016 than in the previous two years.

3. Kernel Volume

Kernel volume in cubic centimeters (cm3) is often indicative of growing conditions. 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

  • Average U.S. Aggregate kernel volume (0.27 cm3) was the same as 4YA (0.27 cm3), but slightly lower than 2014/2015 (0.28 cm3).
  • Kernel volume range (0.23 to 0.31 cm3) was similar to the 2014/2015 range (0.21 to 0.31 cm3) and the 4YA range (0.20 to 0.32 cm3).
  • The kernel volume standard deviation (0.01 cm3) was the same as 2014/2015 and 4YA.
  • Average U.S. Aggregate kernel volumes at export and at harvest were essentially the same (0.27 cm3) in 2015/2016 as for 2014/2015, 2013/2014, and 4YAs.
  • Average kernel volume was smaller for the Pacific Northwest ECA (0.25 cm3) than for the Gulf (0.28 cm3) and Southern Rail (0.29 cm3) ECAs. The Pacific Northwest ECA also had the lowest kernel volume for the previous two years, 4YA, and the 2015 harvest samples.
  • Of the 2015/2016 export samples, 34.4% had kernel volumes equal to or greater than 0.28 cm3, compared with 56.0% in 2014/2015, which indicates a lower percentage of large kernels in 2015/2016 than in the previous year.
  • There is a positive relationship for the 2015/2016 export corn between kernel volume and 100-kernel weight, as shown in the adjacent figure (the correlation coefficient is 0.99).

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 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 indicate very hard corn, which is typically desirable for dry milling and alkaline processing. True densities near the 1.275 g/cm3 level and below tend to be softer, but process well for wet milling and feed use.

RESULTS

  • Average U.S. Aggregate kernel true density (1.275 g/cm3) was lower than 2014/2015 (1.295 g/cm3) and 4YA (1.292 g/cm3).
  • Average kernel true density for the 2015/2016 export samples was higher than for the 2015 harvest samples (1.254 g/cm3), and also in 2014/2015 and 2013/2014. The 4YA export true density (1.292 g/cm3) was also higher than the 4YA harvest true density (1.265 g/cm3). The higher true density found at export is likely due, in part, to the higher 100-k weights that were also found each year at export.
  • For the 2015/2016 export samples, only 51.9% had kernel true densities equal to or above 1.275 g/cm3, compared with 89% found in 2014/2015. This indicates a higher percentage of kernels with soft endosperm in 2015/2016 than in the previous year.
  • Average kernel true densities were essentially the same for the Gulf (1.276 g/cm3), Pacific Northwest (1.275 g/cm3) and Southern Rail (1.273 g/cm3) ECAs.

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 weight percentage of material passing through a screen. 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 for fully 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. Secondly, intact whole kernels are less susceptible to mold invasion during storage and to breakage during handling. Some companies pay contracted premiums for corn delivered above a specified level of whole kernels.

RESULTS

  • Average U.S. Aggregate whole kernels (89.5%) was higher than 2014/2015 (88.4%) and 4YA (88.6%).
  • The average percentage of whole kernels at export was lower than at harvest (94.9%). Whole kernels for the 4YA export samples (88.6%) was also lower than for the 4YA harvest samples (93.5%). The reduction in whole kernels from harvest to export is likely caused by the added handling in transport to export loading locations.
  • The 2015/2016 export samples had a range of 73.6 to 98.4% (with a standard deviation of 3.7%), while the 2015 harvest samples had a narrower range (78.4 to 99.8%) and a lower standard deviation (2.7%). The percentage of whole kernels declined and the standard deviation of whole kernels increased from harvest to export, which occurred not only in 2015/2016, but also in 2014/2015, 2013/2014, and 4YA.
  • The Gulf ECA (90.2%) had a higher whole kernel average compared to the Southern Rail (89.9%) and Pacific Northwest (87.1%) ECAs.
  • The percentage of 2015/2016 export samples with whole kernel percentages greater than or equal to 90% was 49.8%, compared to 45% for the 2014/2015 export samples, and 93.6% for the 2015 harvest samples. The reduction in percentages of whole kernels from harvest to export is most likely due to handling.
  • The whole kernel percentages for contracts loaded as U.S. No. 2 o/b were 89.6%, which was very close to the 90.0% found for contracts loaded as U.S. No. 3 o/b.

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 prefer values between 70 and 85%. However, there are certainly exceptions in user preference.

RESULTS

  • Average U.S. Aggregate horneous endosperm (80%) was lower than 2014/2015 (82%) and 4YA (83%).
  • Average horneous endosperm for the 2015/2016, 2014/2015, and 2013/2014 export samples were within ±1% of the average horneous endosperm for the 2015, 2014 and 2013 harvest samples, respectively.
  • The 2015/2016 export samples for horneous endosperm had a smaller range (74 to 88%) and standard deviation (2%) than the 2015 harvest samples. This same pattern of increased uniformity between export and harvest samples occurred in the previous two years of export samples when compared to the 2014 and 2013 harvest samples, respectively.
  • Average horneous endosperm for the Pacific Northwest ECA (80%) was same as for the Gulf and Southern Rail ECAs (both 80%).
  • Average horneous endosperm for contracts loaded as U.S. No. 2 o/b (80%) was similar to contracts loaded as U.S. No. 3 o/b (81%).
  • Only 54.4% of the 2015/2016 export samples had at least 80% horneous endosperm in contrast to 75% of the 2014/2015 and 79% of the 2013/2014 export samples, indicating many of the 2015/2016 samples had a lower percentage of hard corn than in the two previous years.