Coffee Science, Lavras, v. 13, n. 4, p. 498 - 509, oct./dec. 2018 Cardoso, D. B et al. 498 DETERMINATION OF THERMAL PROPERTIES OF COFFEE BEANS AT DIFFERENT DEGREES OF ROASTING Danilo Barbosa Cardoso 1 , Ednilton Tavares de Andrade 2 , Renso Alfredo Aragón Calderón 3 , Mariane Helena Sanches Rabelo 4 , Camila de Almeida Dias 5 , Isabela Ávila Lemos 6 (Received: June 25, 2018; accepted: September 26, 2018) ABSTRACT: The aim in this study was to determine the main thermal properties of the granular mass of coffee (specifc heat, thermal conductivity, and thermal diffusivity) for different degrees of roasting, as well as to model and simulate thermal conductivity at different degrees of roasting. For determination of specifc heat, the mixing method was used, and for thermal conductivity, the theoretically infnite cylinder method with a central heating source. Thermal diffusivity was simulated algebraically using the results of the properties cited above and of the apparent specifc mass of the product. Thermal conductivity was also simulated and optimized through fnite element analysis software. As results, at darker roasting there was an increase in specifc heat and a reduction in thermal conductivity and thermal diffusivity. Comparing thermal conductivity determined in relation to simulated and optimized conductivity, the mean relative error was 1.02%, on average. Index terms: Specifc heat, thermal conductivity, thermal diffusivity. DETERMINAÇÃO DAS PROPRIEDADES TÉRMICAS DE GRÃOS DE CAFÉ EM DIFERENTES PONTOS DE TORRA RESUMO: Este trabalho teve como objetivo determinar as principais propriedades térmicas da massa granular de café (calor específco, condutividade e difusividade térmica), para diferentes pontos de torra bem como modelar e simular a condutividade térmica em diferentes graus de torração. Para a determinação do calor específco utilizou-se o método das misturas e para a condutividade térmica o método do cilindro teoricamente infnito com fonte de aquecimento central. A difusividade térmica foi simulada algebricamente utilizando-se os resultados das propriedades citadas anteriormente e da massa específca aparente do produto. Condutividade térmica foi, também, simulada e otimizada através do software de análise por elementos fnitos. Como resultado foi observado que em torras mais escuras houve um aumento do calor específco e uma diminuição de condutividade e difusividade térmica. Através da comparação entre a condutividade térmica determinada e a condutividade simulada e otimizada verifcou-se que o erro médio relativo, em média, foi de 1,02%. Termos para indexação: Calor específco, difusividade térmica, condutividade térmica. 1 INTRODUCTION Brazil is leader in the world market for production and export of green coffee beans. In postharvest, these green coffee beans pass through some steps until reaching at a very important phase of processing, the roasting. According to the International Coffee Organization – ICO (2017), the world consumption of coffee was 9368 million of Kg in 2017. The roasting is a highly important step in coffee processing because it is responsible for expressive modifcation of the raw material. During roasting, the coffee bean dehydrates and goes through physical-chemical transformations that provide the fnal product with the characteristics offered for its consumption (color, aroma, and favor) through the formation of various volatile compounds (BOTTAZZI et al., 2012; HERNÁNDEZ; HEYD; TRYSTRAM, 2008). 1,2,3,4,5,6 Universidade Federal de Lavras/UFLA - Departamento de Engenharia/DEG - Cx. P. 3037 - 37.200-000 - Lavras - MG cardosodb@gmail.com, edniltontavares@gmail.com, rensoa.aragonc@gmail.com, marianerabelo1@hotmail.com, camila.almeidadias@gmail.com, isa_lemosti@hotmail.com Throughout production process, coffee beans are subjected to changes in temperature and moisture, and to ensure a quality product in the end of process, it is necessary to know how these changes occur. In this sense, the knowing properties such as specifc heat, thermal conductivity, and thermal diffusivity are relevant for studies of heat and mass transfer in agricultural seed grains (BORÉM et al., 2002). The specifc heat, by defnition, is the amount of heat necessary to raise the temperature of a body by 1°C per unit of mass without change in state. It is essential to know this for determination of the amount of energy required for heating or cooling a food product. The thermal conductivity of a material is the measure of its conduct heat capacity (MOHSENIN, 1980). According to Mohsenin (1980), numerical values of thermal conductivity of solid, granular, and porous materials can to vary according to chemical composition, fuid material content,