Experimental Study of Superheated Steam Roasting of Coffee-Guinea Pepper Blend Powered by a Biogas Furnace

Abstract

Roasting is a crucial step in determining the quality of coffee, particularly for the coffee-Guinea pepper blend widely consumed in Senegal. Guinea pepper (botanical name Aframomum melegueta ) belongs to the Zingiberaceae family and is a spice. However, coffee-Guinea pepper blends on the market often have defects in taste and aroma, mainly due to inefficient, energy-intensive and environmentally harmful conventional roasting techniques (wood, gas or hot air). This study proposes a sustainable, innovative approach that uses superheated steam generated from biogas produced by fermenting cow dung in a 4 m 3 geomembrane biodigester. This Open Access biogas is used to fuel a burner that superheats the steam used for roasting Arabica coffee (11.06% moisture content) and Guinea pepper (8.75% moisture content). The efficiency of the system was assessed through biomethane production, thermal performance, moisture loss, color changes and Fourier transform infrared spectroscopy (FTIR). Results showed that biomethane production reached 59.1% by the 13th day, which was sufficient to generate steam at 250˚C. The coffee reached this temperature in 450 seconds (compared to 600 seconds for hot air), with the moisture content reduced to 1.5%, achieving excellent thermal homogeneity (with a maximum deviation of 5˚C). The guinea pepper was roasted using the residual heat from the coffee beans, reducing its moisture content from 8.75% to 3.23% without the need for any additional energy input. FTIR analysis confirmed the preservation of more aromatic compounds (intact C-H, C=O and C-O bands) than was observed with traditional methods. This approach also significantly reduces energy consumption and CO 2 emissions and eliminates the impact of deforestation.