Study On Dielectric Properties Of Arabica Coffee Bean

The word "coffee" comes from the Greek word 'Kaweh',meaning 'strength and passion'.China's main areas of coffee cultivation in Yunnan,Taiwan,Guangxi,Guizhou.Coffee is one of the main economic objects in Yunnan.Yunnan is the country's largest planting base.Coffee production and processing of intermediate products include:parchment coffee beans,green coffee beans and roasting coffee beans.At present,the domestic arabica coffee bean moisture content can not be real-time online,fast and accurate detection.Based on the dielectric properties of small grains of coffee moisture content detection can be real-time continuous detection online.This paper mainly studies the relationship between the dielectric properties of arabica coffee bean and the influencing factors.Based on the dielectric properties of arabica coffee bean moisture detector and arabica coffee bean different roasting degree of the development of the detector to provide basic data.In this paper,the frequency(1?1000 kHz),temperature(25?45 ?),water content(11.18?43.69%),(9.76?19.69%)were studied with parchment coffee beans,green coffee beans and roasting coffee beans.The roasting degree(light,medium,dark)on the dielectric properties of the test material.And the reasons for the influence of the above factors on the dielectric properties.The prediction model of the moisture content of parchment coffee beans and green coffee beans was established,and the influence of frequency on the relative permittivity was studied.The accuracy and feasibility of the model were verified.The results are as follows:The reason of the change of the dielectric parameters was analyzed,and the relative permittivity and water content prediction models of the parchment coffee beans and Green coffee beans were established.The relationship between the roasted coffee beans and the relative dielectric constant was established.Accuracy and feasibility of verification.The results are as follows:(1)In the measurement frequency of 1?1000 kHz,the relative dielectric constant of the parchment coffee beans decreases with increasing frequency,increases with the increase of water content,with the temperature increases basically unchanged.The dielectric loss factor decreases first then increases with increasing frequency,and increases with the increase of temperature and water content.The relative permittivity of the parchment coffee beans was established at the frequency of 500 kHz.The determination coefficient of mathematical model is 0.9875.The absolute error between the calculated moisture content and the measured moisture content is-3.07?2.47%,and the average absolute error is 1.7%.Indicating that the detection of water content of parchment coffee beans can be obtained by measuring the relative permittivity at 500 kHz.(2)In the measurement frequency of 1?1000 kHz,the relative dielectric constant of coffee beans decreased with increasing frequency.The dielectric loss factor decreases first and then increases with increasing frequency.The relative permittivity and dielectric loss factor increase with increasing moisture content and temperature.The bulk density of coffee beans has no effect on the dielectric parameters.The prediction equation of the water content of coffee beans was established at the test'frequency of 500 kHz.The determination coefficient of mathematical model is 0.9897.The absolute error between the calculated moisture content and the measured moisture content is-0.88?0.75%,the average error is 0.395%.Description the detection of the moisture content of coffee beans can be obtained by measuring the relative permittivity and temperature at 500 kHz.(3)In the measurement frequency of 1?1000 kHz,the relative dielectric constant of the light roasting coffee beans decreases at a certain frequency with increasing frequency.The relative permittivity of medium and dark roasting coffee beans fluctuates within a certain range with increasing frequency.The dielectric loss factor of coffee beans with different baking degree increases with increasing frequency.The relative permittivity and dielectric loss factor of roasting coffee beans increased with the increase of temperature.The relative permittivity gradually decreases with the degree of roasting.The bulk density decreases with the roasting degree.The bulk density has no regular effect on the dielectric parameters.At the measurement frequency of 2 kHz to 800 kHz.The relative permittivity of roasted coffee beans:light roasting>medium roasting>dark roasting.The roasting degree can be reflected by measuring the relative permittivity of the roasted coffee beans.The above test results show that the microcrystalline coffee dielectric properties are an effective way to quickly detect the moisture content and baking degree of coffee beans.