Analysis and technical optimization of processing condition for better quality of robusta coffee production

Abstract

The wet processing of robusta coffee starts with harvesting coffee cherries, followed by sorting the cherries, pulping, fermentation, washing, drying, hard skin hulling, bean sorting, and packaging. Soaking fruit before pulping is an alternative for coffee farmers to delay the pulping process if time does not allow it. The fermentation process aims to remove mucus that is firmly attached to the hard skin. The addition of L. casei microbes can accelerate the process but affect the final taste. The study aimed to optimize the duration of soaking and fermentation processes for obtaining coffee beans with a minimum number of unpeeled beans, minimum partially black bean value, maximum taste quality, and to identify volatile components that play a role in forming the best steeping aroma after the coffee beans are roasted, ground and brewed. Experiments and data analysis were carried out using the Response Surface Method design. The optimization results showed that 24 hours of soaking and 24 hours of fermentation were the optimum treatment based on the criteria for unpeeled beans response, partially black bean value, and total taste score with a desirability value of 0.721. The identified volatile compounds (43) include 9 aldehyde group compounds, 3 alcohols, 4 furans, 5 heterocyclic N, 6 ketones, 1 organic acid, 3 phenols, 10 pyrazines, and 2 thiols. The spicy and chocolaty aroma produced was also the highest among treatments, namely 8.98% and 7.74%. The treatment without soaking and fermentation had the highest percentages of caramelly and nutty areas, namely 23.14% and 21.35%, respectively. Key words: Coffee beans; fermentation; soaking; technical optimization; volatile compound.