1. 1000-Kernel Weight (TKW), Kernel Volume, and Kernel True Density
The 1000-kernel weight (TKW) is determined from the average weight of 300 individual kernel replicates using the Perten Single Kernel Characterization System (SKCS 4100). The instrument weighs each seed to the nearest 0.01 mg and automatically calculates the TKW based on the average weight of the 300 individual seeds. The averaged TKW is reported in grams.
The kernel volume for an accurately weighed 80.00 ± 0.05 g kernel sample is calculated using a helium pycnometer and is expressed in mm3/kernel. The individual kernel volume is obtained by dividing the TKW (g) by the total seed weight (g) used in the pycnometer, and multiplying the recorded pycnometer volume (cm3) by this factor. The value obtained, cm3/1000-kernels, is equivalent to mm3/kernel. Kernel volumes usually range from 12 to 28 mm3 per kernel for small and large kernels, respectively.
True density of kernel samples is calculated by dividing the mass (or weight) of the 80.00 ± 0.05 g externally sound kernels by the pycnometer volume (displacement) of the same kernels, and is reported in grams per cubic centimeter (g/cm3). True densities typically range from 1.24 to 1.39 g/cm3 at “as is” moistures of about 12 to 15%.
2. Kernel Hardness Index
Grain hardness is measured using the SKCS 4100. The SKCS 4100 automatically selects individual kernels, weighs them, and then crushes them between a toothed rotor and a progressively narrowing crescent gap. As a kernel is crushed, the force between the rotor and crescent is measured. About 50 g of clean, externally intact seed is introduced into the instrument hopper. The instrument then automatically characterizes 300 individual seeds. The data are reported as average kernel hardness index, based on the 300 individual seeds. Samples are also classified as hard, mixed, or soft, depending on average hardness index value and hardness distribution among the 300 seeds. Kernel hardness index values can range from 20 to 120.
3. Kernel Diameter
Kernel diameter is measured using the SKCS 4100. The instrument records the individual diameter of 300 seeds, and calculates the average seed diameter in mm.