Water adsorption isotherms of coffee blends

Abstract

This work aimed to evaluate the adsorption isotherms of roasted and grinded coffee, in different blends and storage temperatures. Crude grain coffee of two species were used: arabica (Coffea arabica) and robusta(Coffeacanephora), dehulled and dried. Grain were submitted to a selection to eliminate deteriorated grain, damaged and bored, to obtain a homogeneous raw material, without defects. Grain coffee from both species, after triage, were sent to roasting process at medium light level (Agtron SCAA#65).After roasting process, grain wasprocessed in a Mahlkönig mill, at average particle size (0.84 m). Blends were made in the following proportions of arabica and robusta: 80:20; 60:40 and 40:60.Samples were stored in BOD chambers for 6 months and kept at temperatures of 10 and 30 ºC, with initial moisture content of 2.0 ± 0.3 % (d.b.). At the beginning of storage (time zero) and at 30, 60, 120 and 180 days of storage, moisture content and water activity were determined. Several mathematical models, frequently used to represent the agricultural products hygroscopicity, were fitted to experimental data of sorption. Values of water activity and moisture content varied between 0.1912 and 0.5160; 2.20 and 5.51 % (d.b.), respectively. Modified Oswin model was the one that best represented the adsorption of coffee blends.