The Effect of Freeze Drying and Determination of Heat Transfer on Various Maturity Levels of Robusta Coffee Fruits

Abstract

The quality of coffee beans is influenced by the level of maturity, which can be determined based on the skin color of the coffee fruit and post-harvest processing. The study was conducted to determine the effect of freeze-drying on various variations in the level of maturity of water content, caffeine, and heat transfer value. The freeze-drying method was chosen because it can maintain the chemical content of the food. Robusta coffee was obtained from Karawang Regency, West Java, Indonesia. Coffee fruit is sorted by skin color using a colorimeter. Fresh beans are obtained by stripping the fruit skin and epidermis and washing mucus. Fresh bean is reduced in size until it passes the 18-mesh sieve. Freeze-drying is operated at an initial temperature of -20 °C, sublimation temperature of 40 °C, and operating pressure of 1 to 6 mbar abs. Water content analysis using gravimetric methods, caffeine content analysis using UV-Vis spectrophotometry method, and fat content using the Soxhlet method. The total heat transfer value is determined from the cup to the material. The results showed that the freeze-drying process at semi-ripe to over-ripe maturity levels could reduce the water content to the permissible limit but cannot be used for unripe. The results of the statistical significance test show that the freeze-drying process at various maturity levels can significantly reduce the water content but can maintain the caffeine content in robusta coffee beans. The highest heat transfer value occurs at the un-ripe maturity level of 86.50 kJoule