Analysis of temperature variability during the thermal processing of hazelnuts

The variability in temperature that occurs between hazelnuts during roasting is investigated. Two deterministic models of unsteady state heat transfer in a hazelnut are developed; one is based on the analytical solution for a spherical solid body and the other is a numerical model of heat flow in a hollow sphere. The mean and standard deviation in the thermal and physical properties of hazelnuts have been measured. Also the mean and standard deviation in hazelnut temperature vs. time during a roasting process has been quantified. Theoretical solutions based on functions of random variables are employed to characterise the output of such a thermal process where the rate constants are randomly distributed. In addition, the Monte Carlo method is applied to both the analytical solid sphere and numerical hollow sphere heat transfer models to estimate temperature variability. All three approaches gave satisfactory predictions of mean hazelnut temperature vs. time. However, only the Monte Carlo solution of the numerical hollow sphere model provided a good estimate of the standard deviation in hazelnut temperature vs. time. The prediction of variability in hazelnut temperature during roasting is important in the context of optimising the roasting process with respect to uniformity in product quality and safety.