Convective Drying Behavior of Tarhana Dough

In this study, convective air drying was applied to tarhana dough using an electric pilot oven. A three‐stage drying process was recommended as a means of shortening the overall drying period. This consisted of the drying of one‐side of a thin layer of tarhana dough, a subsequent drying of the reverse‐side thin layer of tarhana dough, followed by that of flake drying, which is obtained after the flaking of the semi‐dried thin layers. The moisture transfer behavior of the thin layers of tarhana dough and flakes was determined by observing the moisture content and drying rate (kg moisture/m²/s) profiles at air temperatures of 60, 80 and 100C, until the equilibrium of the final moisture content. The moisture diffusivities for each stage were predicted by the analytical solution of Fick's second law of diffusion. At each drying temperature, considerably higher effective diffusivity values were obtained for flake drying (16.3–36.4 × 10⁻⁸ m²/s) as compared with thin layer dough drying (0.7–2.6 × 10⁻⁸ m²/s; p < 0.05). The convective drying of tarhana in three stages was then simulated by an implicit finite difference numerical solution using the predicted effective moisture diffusivity values as input. A suitable agreement between the numerical and experimental moisture profiles was achieved. The volatile compounds of tarhana powders and their concentrations were determined by headspace solid‐phase micro‐extraction. A sharp reduction in the concentration of specific volatile compounds with applied air temperatures, which are equal to and higher than 80C, was observed. PRACTICAL APPLICATIONS: Tarhana is a traditional Turkish fermented food and generally consumed as a dry soup mix. Tarhana soup is one of the selected traditional recipes from Turkey, a partner country for inclusion in the work package on “Traditional Foods” of a EuroFIR pilot study, funded under the EU 6th Framework Food Quality and Safety Programme. The drying of tarhana dough is one of the critical steps. In the traditional sun drying method for tarhana dough, a large amount of manual labor is required for homogenous drying. This study recommends mechanical stage‐by‐stage convective oven drying, which can be applied industrially instead of either sun drying or a continual static process. Also presented is the simulation of convective drying of tarhana dough by the implicit finite difference numerical solution, which is a numerical tool to predict the time‐moisture content of the tarhana dough during an industrial convective drying.