The influence of roasting temperature on the physical properties of Arabica and Robusta coffee

The influence of different roasting temperatures on the physical properties of Arabica and Robusta coffee was investigated. Arabica (Rio Minas) of two quality classes and Robusta coffee samples, roasted at 167, 171 and 175°C, were used for this research. Bulk density, total weight loss, water activity, texture and colour of coffee were determined. Total weight loss increased, and bulk density of coffee beans decreased with increasing of roasting temperature. Arabica 1st class with the highest weight and volume also had the highest total weight loss and Robusta had the highest bulk density. Coffee samples roasted at 175°C had significantly lower (P<0.05) water activity values than samples roasted at 167°C and those changes mostly affected mechanical properties of beans. The highest breaking force values had Arabica 1st class, with lower share of black beans, roasted at 167°C and Arabica 2nd class roasted at 171 and 175°C, compared to other samples roasted at the same temperatures. Robusta beans had the most brittle and fragile texture. It can be concluded that texture of coffee depends on the roasting temperature, type and class of coffee as well. L*, a*, and b* colour parameters decreased as the roasting temperature increased, which affected on coffee beverage colour defined as brown (167°C) and dark brown (171°C and 175°C) with different share of yellowish, orange, reddish and grey shades. Sensory analysis can be used as a good tool for a detailed description of coffee colour, as an important indicator of quality, especially in industrial conditions of coffee production.