4.1.5 Material of the drum: stainless steel
Stainless steel is chosen for being widely recommended in food processes. It does not interact
chemically with food. Under high radiation, stainless steel changes color: from reflective, it turns opaque
with a brownish-violet like color. This reduces its reflectivity and improves the thermal efficiency of the
roasting. Especially in the beginning when coffee is of clear green color.
4.1.6 Thermal insulation
Thermal insulation is an important way to reduce heat losses and improve the roaster efficiency.
A textile is chosen for its neutrality with f ood: recycled cotton textiles are used. Although the
temperatures the insulation faces are at the limits of the material resistance.
Cotton has a low thermal conductivity, cotton = 0.06W/m/K providing very good insulation.
A layer of about 5 cm keeps the outer surface of the insulated drum at around 50°C.