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Corn Export Cargo Quality Report 2013/2014

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. Export Corn 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 (16%) was higher than the previous two years, which was likely due to additional drying needed with the 2013 crop; however, the majority of the export samples (70.9%) still had less than 20% stress cracks, and should have reduced rates of breakage during handling.
  • At export, 42.5% of the 2013/14 samples had SCI of less than 40, compared to 82% in 2012/13. This would indicate that more kernels in 2013/14 have double or multiple stress cracks than in 2012/13.
  • Whole kernels (88.6%) was lower than in 2012/13 (89.9%).
  • Both true densities and test weights were significantly lower for 2013/14 than for 2012/13.
  • Horneous endosperm (82%) was lower than 2012/13 (85%) and 2011/12 (84%). This indicates corn endosperm will be less hard than the previous two years.
  • Kernel volume and 100-k weight were significantly lower than in 2012/13 and 2011/12, indicating smaller kernel sizes in early 2013/14 corn exports than in the previous two years.
  • Average 100-k weight 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 samples.

1. Stress Cracks and Stress Cracks 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 outward appearance of the kernel may appear unaffected at frst 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. Stress cracks affect corn in various ways:

  • 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 affect the need for artificial drying and influence the degree of stress cracking found from region to region. Then, as corn moves through the market channel, some stresscracked 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 percent of multiple stress cracks. Multiple stress cracks are generally more detrimental to quality changes than single stress cracks.

RESULTS

  • U.S. Aggregate stress cracks was 16%, significantly higher than in 2012/13 (9%).
  • Stress crack percentages were higher than found at harvest for the 2013 crop corn (16% vs 9%). Increases in stress cracks also occurred with the 2012 and 2011 corn crops, and these increases may be attributed, in part, to conditioning and additional handling from the harvest elevator to the export terminal.
  • Stress cracks ranged from 0 to 49% with a standard deviation of 7%.
  • Almost 29.1% of the samples had greater than 20% stress cracks, compared to 9% and 7% in the previous two years. About 54.6% of the samples had greater than 15% stress cracks, compared to 2012/13 (16%) and 2011/12 (19%). This indicates a portion of the corn is experiencing higher stress cracks than in the previous two years. However, the majority of the samples (70.9%) still had less than 20% stress cracks, and should have reduced rates of breakage during handling.
  • Stress cracks averaged 16%, 18% and 16% for the Gulf, Pacific Northwest and Southern Rail ECAs, respectively.
  • The variability of stress cracks (standard deviation) was the same (7.0%) across all ECAs.
  • Stress cracks for Gulf ECA contracts loaded as U.S. No. 2 o/b was 15%, significantly lower than the 18% in Gulf ECA contracts loaded as U.S. No. 3 o/b. The higher stress cracks found in U.S. No. 3 o/b is consistent with the higher BCFM (3.0%) compared to the lower BCFM level (2.8%) found in U.S. No. 2 o/b contracts.

RESULTS

  • U.S. Aggregate stress crack index (SCI) average of 46.1 was significantly higher than in 2012/13 (25.9).
  • SCI ranged from 0 to 176 with a standard deviation of 24.9.
  • SCI at export was higher than the SCI found at harvest (22.8).
  • The SCI for the Southern Rail ECA (41.3) was lower than for the Gulf (47.2) and Pacific Northwest (45.3) ECAs.
  • SCI standard deviations were nearly the same across all ECAs (26.4, 21.7 and 21.3 for Gulf, Pacific Northwest and Southern Rail, respectively).
  • At export, 42.5% had SCI of less than 40, compared to 2012/13 (82%). This would indicate more kernels in 2013/14 had double or multiple stress cracks than in 2012/13.
  • SCI for Gulf ECA contracts loaded as U.S. No. 2 o/b was 41.9, which was significantly lower than the 54.9 found for Gulf ECA contracts loaded as U.S. No. 3 o/b. Thus, both stress crack percentages and SCI were lower for the Gulf contracts loaded as U.S. No. 2 o/b than for Gulf contracts loaded as U.S. No. 3 o/b.

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 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 averaged 34.95 g with a range of 25.13 to 41.86 g. This 100-k weight was significantly lower than in 2012/13 (35.86 g).
  • 100-k weight was significantly higher than for the 2013 harvest corn (33.41 g). Higher average 100-k weight at export than at harvest has been seen in each of the past three years. 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 2013/14 export samples had greater uniformity than the 2013 harvest samples as indicated by a tighter range and lower standard deviation.
  • The average 100-k weight was significantly lower for the Pacific Northwest ECA (28.94 g) than for the Gulf (36.26 g) or Southern Rail (36.91) ECAs. The same pattern was observed in the previous two years.
  • About 70% of the 2013/14 export samples (76% in 2012/13) had 100-k weight of 34.0 g or greater.

3. Kernel Volume

Kernel volume in cubic centimeter (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 (0.27 cm3), lower than found in 2012/13 (0.28 cm3), was the same as for the 2013 harvest samples.
  • Kernel volume ranged from 0.20 to 0.32 cm3.
  • The standard deviation of 0.02 cm3 was the same but the range was less in the 2013/14 export samples than in the 2013 harvest samples.
  • As in the previous two years, the average export kernel volume was significantly smaller (0.23 cm3) for the Pacific Northwest than for the Gulf (0.28 cm3) and Southern Rail (0.29 cm3) ECAs. Average kernel volume was also smaller for the harvest samples in the Pacific Northwest ECA than in the other two ECAs in 2013 and 2011.
  • Approximately 72.6% of the 2013/14 export samples had kernel volumes equal to or greater than 0.26 cm3, compared with 77% in 2012/13.

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 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 1.287 g/cm3 and was significantly lower than found in 2012/13 (1.297 g/ cm3).
  • Average kernel true density for the 2013/14 export samples was significantly higher than for the 2013 harvest samples (1.258 g/cm3). Average true density was also higher at export than at harvest in the previous two years. 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, 78.4% had kernel true densities equal to or above 1.275 g/cm3, compared with 95% found in 2012/13.
  • There is a weak but positive relationship for the 2013/14 export corn between 100-k weight and true density as shown in the graphic show at the lower right. (The correlation coefficient is 0.76.)
  • The Pacific Northwest had the lowest average true density and 100-k weight among ECAs for each of the past three years.

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.

The exterior integrity of the corn kernel is very important for two key reasons. First, it affects water absorption for alkaline cooking operations. Kernel nicks or cracks allow water to enter the kernel faster than for fully intact or whole kernels. Too much water uptake during cooking can result in 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 extra premiums for contracted corn delivered above a specifed level of whole kernels.

RESULTS

  • U.S. Aggregate whole kernels averaged 88.6% and was significantly lower than in 2012/13 (89.9%).
  • The average percent of whole kernels at export was significantly lower than found at harvest (92.4%).
  • The 2013/14 export samples had more variability (range of 70.4 to 97.6% with a standard deviation of 4.6%) than the 2013 harvest samples (range of 73.6 to 99.6% and standard deviation of 3.7%).
  • Whole kernel averages for the Gulf (88.5%), Pacific Northwest (89.3%) and Southern Rail (87.8%) ECAs were not significantly different from one another.
  • The percent of samples that had whole kernel percentages greater than or equal to 90% was 43.7%, compared to 52% of the 2012/13 export samples.
  • The whole kernel percentages for contracts loaded as U.S. No. 2 o/b were 88.0%, somewhat lower than the 89.6% 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. 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%, significantly lower than in 2012/13 (85%).
  • The 2013/14 export samples ranged from 75 to 94% and had a smaller range and standard deviation than the 2013 harvest samples.
  • The horneous endosperm for the Pacific Northwest ECA was significantly lower (79%) than that for the other two ECAs (both 83%).
  • Average horneous endosperm was lower (82%) for contracts loaded as U.S. No. 2 o/b than for contracts loaded as U.S. No. 3 o/b (84%).
  • At export, 79.1% of the samples had greater than 80% horneous endosperm in contrast to 2012/13 (99%).