Mathematical modeling of survival and weight loss of Baker's yeast during drying

Drying and death rates of Baker's yeast were studied in a computer-controlled laboratory scale tunnel drier with varying air velocity between 2.0–3.0 ms −1 and temperatures within the range of 40–60°C. Two falling rate periods were observed during the drying process. A single first-order expression described the death rate of the microorganisms during both drying phases. Arrhenius-type expressions described the effects of the temperature on the first falling rate period drying and death rate constants. Compensation relations were also found between the parameters of these Arrhenius expressions. A single linear relation was observed between the first falling rate period drying constant and the death rate constant at 2.5 with 3.0 m s −1 for air velocity. A similar relation was also observed with the data obtained at 2.0 m s −1 of air velocity. It was concluded that the death rate of yeast was lower with a slower air velocity. The second falling rate period is a diffusion-controlled process. It was confirmed by the experimental results that the velocity of air flow does not affect the drying rate constants in the second falling rate period. Within the range of the experiments, no temperature effects were observed on the second falling rate period drying constant.