Secagem de cafés descascados submetidos a diferentes umidades relativas do ar de secagem após meia seca

Abstract

Drying is one of the main influencing factors on the final quality of the drink coffee and although to be an operation of routine, factors as the exposition of the product the high temperatures can cause damages in the quality. Thus, the use of low relative humidity of the drying air if became a good alternative, by combining minors temperatures with bigger speeds of drying. The objective of this work was to study the influence that different relative humidity of the drying air after partial drying it has on drying of kinetic and quality of the peeled coffees. The selective harvest of the fruits of Arabica coffee (Coffea Arabica L.) was accomplished in Nepomuceno-MG, being later directed the Federal University of Lavras, where was accomplished the separation for density, the processing by wet, resulting in the portion of peeled coffee and the drying of the grains. Eleven treatments of drying were accomplished, being nine results of the combination of three dry bulb temperatures (40 °C-40 °C; 40 °C-35 °C and 35 °C-35 °C) and three dew point temperatures (2,6 °C; 10,8 °C and 16,2 °C), more two treatments without the control of the dew point temperatures, dried to 40 °C-40 °C and 35 °C-35 °C each. The control of the relative humidity by means of the dew point temperature was made after the grains reach the moisture contents of 0,428 b.s.. The models of Approach of Difusão and Modified Midilli were the most adequate for describing the drying process of the first one and second part of drying respectively. The effective diffusivity coefficient of water in coffee grains varied of 0,81 x 10 -11 the 1,84 x 10 -11 m² .s -1 during the first part of the drying and varied of 1,49 x 10 -11 the 3,29 x 10 -11 m² .s -1 during the second part of the drying, increasing significantly with the reduction of the dew point temperature and increase of the dry bulb temperature. For same one dry bulb temperature, the reduction of the dew point temperature and consequently the relative humidity, increases the drying rate and reduced drying time of the coffee grains. Submitted coffees the drying with dry bulb temperature of 40 °C and dew point temperature of 16,2 °C (RH of 25%) are indicated for production of coffees of bigger quality in smaller times. According the climatic characteristics of each region and aiming at bigger quality, indicates drying temperatures of 35 °C for the “Cerrado Mineiro” and 40 °C-35 °C for “Sul de Minas”. For region of “Matas de Minas”, the combination of drying temperature of 40 °C-35 °C is not indicated for production of coffees from better quality. Dew point temperature of 16,2 °C (UR of 25%), results in coffees with bigger cellular integrity when exposed the temperatures of to 40 °C. For region “Sul de Minas”, the drying temperature agreed of 40 °C-35 °C, keeps the preserved cellular structure.