An Experimental Design on Coffee Extraction Factors Impacting the Measurable Percent of Total Dissolved Solids in Solution

Abstract

There are numerous techniques and technologies used in the brewing of coffee today. This study is aimed to design an umbrella experiment to examine the impacting key factors consistent across all methods of extraction. These factors were identified as: grind size, roast type, steep time, grind to water as a mass-to-mass ratio and temperature. Samples were prepared by grinding the beans, weighing the beans and adding the appropriate amount to a rectangular glass vessel. Distilled water was used. French press was selected as the brewing technique. No agitation after the addition of grind was allowed. Water was heated to initial temperature and added to the vessel and a timer was started. Upon time completion aliquots were taken and analysed using a prism-based automatic temperature compensation (ATC) refractometer. Minitab 19.2020.1 (64-bit) was used for analysis of variance and optimisation. In the initial design of experiments, the five factors were considered at different levels. Three factors found significant in impacting %TDS (total dissolved solids) were: total steep time, grind-to-water ratio and roast type. To further refine the experiments, 2³ full-factorial design was conducted for these three factors. Finally, optimisation was done to determine the factor levels to produce a cup of coffee for the target %TDS of 1.26. This research found that it is best to use medium roast coffee that is ground fine with a 0.08 grind-to-water ratio, with an initial temperature of 195 Fahrenheit in a French press, and the ideal steep time is 7 min. Previous studies have focused on the extraction methods. In this study, the method of extraction has been removed as a variable. Hence, the findings are very useful for food industry.