Kinetics of almond skin separation as a function of blanching time and temperature

• Kinetics of almond blanching at all tested temperatures were logistic and sigmoidal.
• Blanching rates were not significantly different between 100 °C and 90 °C (212–194 °F).
• The rate of blanching decreased quickly below 90 °C (194 °F).
• Harvest at hull-split then forced hot air drying did not appear to reduce skin adherence.
• Blanching D and z values were more temperature-sensitive than Salmonella Enteritidis PT 30.

This study was undertaken to better characterize the process of almond seed coat (a.k.a. skin) separation via hot water submersion, a process often referred to as ‘blanching’. The degree of skin separation on individual almonds was measured after varying treatment times and temperatures, and modeled empirically. At all tested temperatures (100–70 °C), separation progressed along a sigmoidal logistic curve. Applying the concepts of microbial lethality kinetics to seed coat separation, Dseparation values were 24 s at 90 °C (194 °F), 118 s at 80 °C (176 °F), and 443 s at 70 °C (158 °F). From these, the zseparation value between 70 °C and 90 °C was 15.85 °C. The skin separation rate decreased quickly below 90 °C (194 °F). By comparing the rate of seed coat separation, almond varieties, as well as growing, harvesting, and processing conditions could be quantitatively evaluated for their impact on skin separation.