Estudo de diferentes processos de torração de café por metodo convencional e microondas

AUTOR(ES)

Marta Weber do Canto

DATA DE PUBLICAÇÃO

2001

RESUMO

The objective of this study was to contribute a greater knowledge about different coffee roasting processes by both conventional and microwave methods, comparing the effects on different qualities of arabica coffee (hard to better, soft and very soft). Thus experimental coffee roasting conditions were developed [domestic and rapid (industrial) at 210°C and 220°C] using a laboratory scale roaster, and by microwaves at 3500W, 3700Wand 3850W at a frequency of 2450 MHz, in a pilot rotary dryer combined with hot air. The heating system using microwaves resulted in an increase in quality in the lowest quality coffee sample studied (hard to better), when roasted at 3500W and at 3700W, improving from a classification of hard to better with strong acidity to soft with considerable acidity. However, with the soft coffee sample, the use of microwaves at 3500W only maintained this classification, and at 3700W, resulted in a decrease in quality. Under the conditions studied, it was not possible to roast the very soft coffee sample using microwaves. Thus a technology with potential for development, especially for application in lower quality coffees, was demonstrated. The physical parameters [apparent density, bean diameter, bean swelling, increase in volume and size, water activity, pH, ionic concentration, CIELAB colour and loss of weight] of the rawand roasted coffees, were evaluated for the different heating conditions by both conventional and microwave systems. The dielectric properties (attenuation coefficient, depth of penetration, dielectric coefficient, dielectric loss factor, dielectric loss tangent, phase coefficient and velocity, dielectric conductivity, electric field intensity, energy dissipated per volume, factor and tangent of the effective dielectric loss) of the coffees were also determined, in order to evaluate the behaviour under the action of microwaves, and relate this to the microwave roasting process. Caffeine, 5-caffeoylquinic acid and caffeic acid were determined in both the raw and roasted coffees by HPLC, so as to relate them to the different roasting processes and to the different qualities of arabica coffee. Sensory tests were carried out by qualified coffee tasters and classifiers. The use of the dielectric properties to evaluate the microwave process allowed for a greater understanding of the phenomena occurring during the roasting of coffee, and thus forecast and evaluate the behaviour of the coffee when submitted to a determined electromagnetic field. In the raw coffee bean of the hard to better sample, a greater mean apparent density in a bean with a greater diameter, that is, a more compact green bean structure in relation to the other coffee qualities, resulted in the following effects on the dielectric properties: a greater attenuation constant, greater depth of penetration, lower intrinsic impedance (greater reflection and lower transmission), greater dielectric coefficient, greater dielectric loss, greater dielectric conductivity, greater phase coefficient and velocity, in a smaller tangent of dielectric loss. These effects, at the different microwave powers, resulted in roasted coffees with a lower rate of temperature increase, a lower intensityo f electric field (Erms)at 3500Wand 3700W and a smaller weight loss (but with lower values for luminosity L*), as compared to the soft coffee. The sensory classification of these coffees, roasted at 3500W and at 3700W, was soft coffees with considerable aeidity. The hard to better eoffee roasted at 3500W, exhibited a greater L* and greater "f factor, a greater degree of thermal destruction on the bean surface as compared to that in the internal part of the grain, a greater degree of thermal lack of uniformity. When roasted at 3700W, it showed a lower positive ~L* and lower positive "f factor, and, together with this, less thermal destruction on the bean surface and a greater degree of lack of uniformity with the thermal treatment

ASSUNTO(S)

microondas cafe - torrefação

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