The key aims of this work were to 1) develop a numerical model that would be capable of predicting fluidised-bed dryer operating parameters (including bed temperature, air humidity, and solids moisture content), 2) find the key parameters affecting the viability of yeast, and 3) predict the viability of yeast throughout the drying process. The numerical model developed uses the reaction engineering approach to estimate the drying kinetics and has a strong physical basis with the only fitted parameters being those used for the GAB isotherm. Agreement between model predictions and experimental data was excellent, the maximum root-mean-square errors were 3.1 °C, 1.8 g of water per kg of dry air, and 2.3% in the bed temperature, air humidity and the final moisture content on a wet-basis, respectively. In the second portion of this study, the effect of drying conditions on the viability of yeast cells was studied to gain an improved understanding of the mechanisms affecting yeast viability during fluidised-bed drying. The results of this research showed the major viability losses (dead cells) only occurred when the moisture content on a wet-basis was below 15%. It was also found lower bed temperatures (30-40 °C) resulted in fewer compromised cells than higher bed temperatures (above 40 °C) for moisture contents below 15%. In the final chapter, a response surface model has been fitted using IBM SPSS® (V.24) to predict the viability as a function of both temperature and moisture content, wet-basis. The response surface model was combined with the numerical model to give predictions of the viability as a function of the operating conditions. The model predictions and experimental observations showed good agreement, with the root-mean-square error in the viability predictions being less than 3%.