Shell hardness in almond: Cracking load and kernel percentage

Shell-cracking load was measured in a sample of 54 almond cultivars, most of them from the autochthonous germplasm of Majorca (Spain), through a compression test. The shell-cracking load ranged from 58 N in 'Nonpareil' to 1415 N in 'Alzina', showing the large variability of shell hardness in almond nuts, distributed in 21 mean groups. The results confirmed the suitability of this method for estimating shell hardness due to its reproducibility and small variance within cultivars. Although shell hardness has been traditionally correlated with shelling percentage, our results show that shell hardness may be an independent variable due to its weak correlation with shelling percentage, nut weight and kernel weight. Additionally, our results show that the hardness scores in almond need to be revised.