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Corn Export Cargo Quality Report 2014/2015

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
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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, 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 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 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 stress cracks (14%) was lower than 2013/2014 (16%) but above 3YA (12%); however, the majority of the export samples (79.1%) had less than 20% stress cracks, and should have low rates of breakage during handling.
  • At export, 67.1% of the 2014/2015 samples had a Stress Crack Index (SCI) of less than 40, compared to 43% in 2013/2014. This would indicate that fewer kernels had double or multiple stress cracks in 2014/2015 than in 2013/2014.
  • Whole kernels at export (88.4%) was similar to 2013/2014 (88.6%) and 3YA (88.7%).
  • Both true densities and test weights were higher for 2014/2015 than for 2013/2014.
  • Horneous endosperm (82%) was the same as 2013/2014 (82%) but lower than 3YA (84%).
  • The true density (1.295 g/cm3) is higher than 2013/2014 (1.287 g/cm3) and 3YA (1.291 g/ cm3). The true density and horneous endosperm tests indicate hardness will be unchanged or slightly higher than last year.
  • Kernel volume and 100-k weight were higher than 2013/2014 and 3YA, indicating larger kernel sizes in 2014/2015 corn exports than the previous year and 3YA.
  • Average 100-k weight, kernel volume and true density were lower for the Pacific Northwest ECA than for the other ECAs, indicating smaller kernel sizes and lower true densities for the Pacific Northwest ECA than for the Gulf and Southern Rail ECAs.

4. Stress Cracks and Stress Crack Index (SCI)

Stress cracks are internal fssures 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 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, increasing 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 through the merchandising channel.

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 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 of the kernels have multiple stress cracks (more than 2 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 valuable 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: STRESS CRACKS

  • Average U.S. Aggregate stress cracks were 14%, lower than 2013/2014 (16%), but higher than 3YA (12%).
  • Stress crack percentages (14%) were higher than found at the 2014 harvest (8%). Stress cracks ranged from 0 to 40% with a standard deviation of 7%, indicating more uniformity than 2014 harvest samples with a range of 0 to 100% and a standard deviation of 9%.
  • Of the export samples, 79.1% had less than 20% stress cracks, compared to 71% in 2013/2014. These samples (79.1%) with less than 20% stress cracks should have relatively low rates of breakage during handling.
  • Stress cracks averages were 15%, 12%, and 12% for the Gulf, Pacific Northwest, and Southern Rail ECAs, respectively. The Southern Rail ECA also had the lowest 3YA for stress cracks among all ECAs.
  • The variability of stress cracks (standard deviation) was nearly the same (6 to 7%) across all ECAs.
  • Stress cracks for contracts loaded as U.S. No. 2 o/b was 13%, lower than the 15% for contracts loaded as U.S. No. 3 o/b. The lower stress cracks for contracts loaded as U.S. No. 2 o/b is consistent with their lower BCFM levels (2.7%) compared to the higher BCFM levels (3.6%) for contracts loaded as U.S. No. 3 o/b.

RESULTS: STRESS CRACK INDEX (SCI)

    • Average U.S. Aggregate stress crack index (SCI) (33.3) is close to 3YA (34.3) but lower than 2013/2014 (46.1).
  • SCI ranged from 0 to 116 with a standard deviation of 20.4.
  • SCI at export was higher than the SCI found at harvest (20.2).
  • The Southern Rail ECA (23.0) had the lowest SCI compared to the Gulf (37.7) and Pacific Northwest (24.4) ECAs. The Southern Rail ECA also had the lowest SCI for 3YA and the 2014 harvest samples. The lower SCI and stress crack percentages found for the Southern Rail ECA may, in part, be due to all of the corn contracted for the Southern Rail ECA being U.S. No. 2 o/b.
  • SCI standard deviations across ECAs were 21.6, 16.2, and 20.2 for Gulf, Pacific Northwest, and Southern Rail ECAs, respectively.
  • At export, 67.1% had SCI of less than 40, compared to 2013/2014 (43%). This would indicate fewer kernels in 2014/2015 had double or multiple stress cracks than in 2013/2014.
  • SCI for contracts loaded as U.S. No. 2 o/b (31.4) was lower than for contracts loaded as U.S. No. 3 o/b (36.1).

5. 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 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

  • U.S. aggregate 100-k weight averaged 36.08 g with a range of 26.22 to 40.86 g. This 100-k weight was higher than 2013/2014 (34.95 g) and 3YA (35.31 g).
  • 100-k weight was higher than for the 2014 harvest corn (34.03 g). Higher average 100-k weight at export than at harvest has been seen in the past two years and for 3YA. Since the 100-k weights are based on 100 fully intact kernels, any breakage occurring in transit could have selfselected out smaller kernels that might have been soft or more prone to breakage.
  • The 2014/2015 export samples had greater uniformity than the 2014 harvest samples as indicated by a tighter range and lower standard deviation.
  • The average 100-k weight was lower for the Pacific Northwest ECA (31.95 g) than for the Gulf (37.05 g) or Southern Rail (37.20 g) ECAs. The Pacific Northwest had the lowest average 100-k weight of the three ECAs in the previous two years and 3YA.
  • Of the 2014/2015 export samples, 82.9% had 100-k weight of 34.0 g or greater, indicating larger kernels in 2014/2015 than in previous years (70% in 2013/2014 and 75.5% in 2012/2013).
  • There is a weak but positive relationship for the 2014/2015 export corn between 100-k weight and true density as shown in the graphic at the lower right (the correlation coefficient is 0.68).

 

 

6. 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 kernel volume (0.28 cm3) was higher than 2013/2014 (0.27 cm3), 3YA (0.27 cm3), and the 2014 harvest samples (0.27 cm3).
  • Kernel volume ranged from 0.21 to 0.31 cm3, which is similar to the 2013/2014 range and to the 3YA range (0.20 to 0.32 cm3).
  • The standard deviation of 0.01 cm3 was lower and the range was less in the 2014/2015 export samples than in the 2014 harvest samples.
  • 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 for 2014/2015 export samples. The Pacific Northwest ECA also had the lowest kernel volume for the previous two years, 3YA, and the 2014 harvest samples. Of the 2014/2015 export samples, 55.7% had kernel volumes equal to or greater than 0.28 cm3, compared with 45% in 2013/2014.
  • It can be seen that kernel volume is positively correlated to 100-k weight (the correlation coefficient is 0.99).

7. 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 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

  • Average kernel true density (1.295 g/cm3) was higher than 2013/2014 (1.287 g/cm3) and 3YA (1.291 g/cm3).
  • Average kernel true density for the 2014/2015 export samples was higher than for the 2014 harvest samples (1.259 g/cm3). Average true density was also higher at export than at harvest in the previous two years. The 3YA true density (1.291 g/cm3) was also higher than the 3YA harvest true density (1.267 g/cm3). This higher true density at export is likely due, in part, to the higher 100-k weights that also occurred each year at export.
  • For the export samples, 88.6% had kernel true densities equal to or above 1.275 g/cm3, compared with 79% found in 2013/2014.
  • The Pacific Northwest had the lowest average true density (1.273 g/cm3) and 100-k weight (31.95 g) among ECAs in 2014/2015, in each of the past two years and for 3YA. The Pacific Northwest also consistently had the lowest test weight among all ECAs the past two years and 3YA. True density and test weight are also weakly but positively correlated with each other (the correlation coefficient is 0.69) as shown in the accompanying figure.

8. 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 (88.4%) was similar to 2013/2014 (88.6%) but somewhat lower than 3YA (88.7%).
  • The average percent of whole kernels at export was lower than at harvest (93.6%). Whole kernels for the 3YA export samples (88.7%) was also lower than for the 3YA 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 2014/2015 export samples had a range of 66.4 to 97.0% (with a standard deviation of 4.6%), while the 2014 harvest samples had a wider range (63.6 to 99.8%) but a lower standard deviation (3.5%). The higher standard deviation at export than at harvest also occurred in 2013/2014, but not in 2012/2013.
  • The Southern Rail ECA had a higher whole kernel average (91.2%) compared to the Gulf (88.0%) and Pacific Northwest (88.0%) ECAs. The 3YA places the Pacific Northwest ECA with the highest whole percentages even though 2014/2015 samples did not show this.
  • The percent of samples that had whole kernel percentages greater than or equal to 90% was 44.7%, compared to 44% for the 2013/2014 export samples, and to 85.7% for 2014 harvest samples. This comparison of export distribution to 2014 harvest distribution shows the large reduction of samples with over 95% whole kernels that occurs due to handling.
  • The whole kernel percentages for contracts loaded as U.S. No. 2 o/b were 88.8%, somewhat higher than the 88.3% found for contracts loaded as U.S. No. 3 o/b. This result was consistent with the fact that contracts loaded as U.S. No. 2 o/b also had lower BCFM and lower stress cracks than corn loaded as U.S. No. 3 o/b.

9. 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

  • U.S. Aggregate horneous endosperm averaged 82%, the same as 2013/2014 (82%), unchanged from 2014 harvest samples (82%), but lower than 3YA (84%).
  • The 2014/2015 export samples ranged from 72 to 89% and had a smaller range and standard deviation than the 2014 harvest samples. This same pattern of increased uniformity between export and harvest samples occurred in 2013/2014 and 2012/2013 export samples when compared to 2013 and 2012 harvest samples, respectively.
  • The horneous endosperm for the Pacific Northwest ECA (79%) was lower than for the Gulf and Southern Rail ECAs (82% and 82%, respectively). The Pacific Northwest also had the lowest horneous endosperm in 2013/2014 and 3YA.
  • Average horneous endosperm was slightly higher for contracts loaded as U.S. No. 2 o/b (82%) than for contracts loaded as U.S. No. 3 o/b (81%).
  • At export, 74.9% of the samples had greater than 80% horneous endosperm in contrast to 2013/2014 (79%) and 2012/2013 (99%), indicating many samples have a lower percentage of hard corn in 2014/2015 than in the two previous years.