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 grams per cubic centimeter (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 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.
Average U.S. Aggregate kernel true density (1.258 g/cm3) in 2016 was higher than 2015 (1.254 g/cm3), and lower than 2014 (1.259 g/cm3) and 5YA (1.263 g/cm3).
Variability, based on the standard deviation, for true densities in 2016 (0.018 g/cm3) was higher than 2015 (0.017 g/cm3), but less than 2014 (0.020 g/cm3) and 5YA (0.019 g/cm3).
True densities ranged from 1.162 to 1.320 g/cm3 in 2016, 1.166 to 1.327 g/cm3 in 2015, and 1.160 to 1.340 g/cm3 in 2014.
About 23% of the 2016 samples had true densities at or above 1.275 g/cm3, compared to 18% of the samples in 2015 and 30% in 2014. Since corn with values above 1.275 g/cm3 is often considered to represent hard corn and corn with values below 1.275 g/cm3 is often considered to represent soft corn, this kernel distribution indicates slightly softer corn in 2016 and 2015 than in 2014.
In 2016, kernel true densities for the Gulf, Pacific Northwest, and Southern Rail ECAs averaged 1.259 g/cm3, 1.253 g/cm3, and 1.261 g/cm3, respectively. Pacific Northwest average true density and test weight were lower than the other ECAs’ values in 2016, 2015, 2014, and 5YA.
Test weight, also known as bulk density, is based on the amount of mass contained in a quart cup. While test weight is influenced by true density, as shown in the adjacent figure (resulting in a correlation coefficient of 0.75), it is also affected by moisture content, pericarp damage (whole kernels), breakage, and other factors. In 2016, test weight was 58.3 lb/bu, which was similar to 58.2 lb/bu found in 2015 and higher than 57.6 lb/bu found in 2014.