Performance Evaluation of a Conductive Rotary Dryer for Peanut Roasting

Roasting is a critical step in the preparation of peanuts for use as snacks and in processing of the nuts into oil, butter and flour. A rotary dryer developed at Sandel Engineering, Ile-Ife, Osun State Nigeria, for roasting peanuts, was evaluated. Using the Taguchi experimental design method, nine experiments were conducted to evaluate the effects of four operational parameters: quantity of peanuts, drum speed, airflow rate and drum temperature on the quality of roasted peanuts. The moisture content of the roasted samples ranged from 1.13% to 3.22%. The Taguchi method revealed signal to noise ratios of 4.05, 2.26, 0.37, and 5.41 for the four parameters respectively, their contributions were 30.34%, 7.87%, 1.85%, and 59.95%. Drum temperature emerged as the most critical parameter, followed by peanut quantity, drum speed, and airflow rate. The optimal roasting conditions were identified as a peanut quantity of 5 kg, drum speed of 60 rpm, airflow rate of 0.9 m³/hr, and drum temperature of 150°C. The machine’s roasting efficiency ranged between 68.55% and 88.46% across the nine experimental runs. The sensory evaluation revealed a preference for the sample which had a final moisture content of 1.78%, scoring the highest in colour, taste and overall acceptability.

⓿ Drum temperature is the most critical factor affecting roasting of peanuts in the assessed rotary dryer.

⓿ Acceptable roasted samples have 1.13% to 3.22% moisture content.