Studies on roasting of wheat using fluidized bed roaster

Abstract

Roasting is normally done to enhance the flavour and to improve organoleptic properties of the food grains. Roasting is a high temperature short time (HTST) heat treatment process and the temperatures used are normally in the range of 280–350 °C. In the present study a continuous fluidized bed roaster (FBR) using flue has been designed and used to roast wheat grain. The product obtained thus has been compared to that obtained by using a traditional method, i.e., roasting in a bed of hot sand. Parameters such as moisture content, bulk density, product colour, crispness, microstructure, and total and acid insoluble ash, are considered in the study. Sand contamination in traditionally roasted wheat has been shown by the presence of acid insoluble ash (0.12%). The bulk density decreased from 833 kg/m³ for raw wheat to 526 and 555 kg/m³ for sand and fluidized bed roasted wheat, respectively. The moisture content decreased from 10% to 3% for sand as well as fluidized bed roasted wheat. Colour (expressed as Chroma) of the sand roasted wheat was in the range of 18–32 and that of the fluidized bed roasted wheat 23–32. Textural measurements in terms of compressive strength was between 222–331 N and 129–299 N for sand and fluidized bed roasted wheat, respectively. It is noted that the optimally roasted wheat using FBR has peak force of 30 N with colour (Chroma) value of about 31, total ash of 1.2% and acid insoluble ash of 0.04%. SEM images of the microstructure have indicated FB roasted wheat to have greater porosity which will result in this wheat requiring lower energy for size reduction.