The analysis of Si/Al ratio on CGA decomposition in Indonesian traditional Kreweng pottery coffee roaster to maximize coffee acidity

Abstract

The use of pottery pans lowers the roasting temperature and gives the product a more favorable taste. This study uncovers the role of pottery particle on chlorogenic acid (CGA) decomposition during roasting process. This study aims to design pottery pans and the roasting process that optimize the CGA content and quality of the coffee using Indonesian traditional ceramics from Banyuwangi, East java named Kreweng. The pottery was ground to between 74–1000 µm before activation. The elemental, phase, and morphology characterization performs on the coffee bean. The morphology characteristic of the pottery observed further using digital imaging technique to unravel the pores and boundaries. The impact of the pottery usage for coffee roasting also tested through coffee product pH measurement. The pottery morphology determines coffee product acidity. The smaller the pottery catalyst particle size results in more acid coffee. The pore and grain boundary concentration increases as the particle size decreases. At the same time, the Si/Al ratio was higher at the smaller catalyst particle size with higher porosity, grain boundaries, and absorption. The porosity and defects reveal the negatively charged faces of the pottery crystal edges. The charged faces revealed due to the pottery crystal vibration in response to heat during roasting process. The effectiveness of surface contact is greater due to the distribution of negative charges around the pores that attract OH- side of CGA. This interaction traps hydrogen proton on catalyst conductive surface. As a result, the CGA decomposes into several groups of atoms and molecules including H2 and CO2. The interaction with the catalyst transforms the macronutrient into aliphatic acid. Therefore, roasting media with a higher Si/Al ratio at smaller particle sizes with high micropores will increase the rate of decomposition and the acidity of coffee products.