Condiciones de operación de un biorreactor para la fermentación en café

Las fermentaciones con temperatura controlada se proponen como alternativa de procesamiento para obtener beneficios en la calidad del café. Las características físicas cambiantes en la masa de café, durante la fermentación, se convierten en un desafío para que el sistema de agitación logre condiciones homogéneas de temperatura. Con el objetivo de determinar las condiciones de operación de un biorreactor para fermentaciones en café, se realizó un proceso de puesta a punto, en el que se realizaron fermentaciones con variación en la velocidad de rotación, tiempo de agitación y periodo entre agitaciones. Posteriormente se determinó el comportamiento de las fermentaciones en un rango de temperatura entre 10 y 30 ºC, con intervalos de 5 ºC. Como testigo de cada proceso se realizó una fermentación espontánea. Se determinaron los tiempos de degradación de mucílago mayor a 95 % y de equilibrio de temperatura entre la masa y la chaqueta del equipo. Se observaron diferencias en el tiempo de fermentación y los valores finales de pH y temperatura de la masa, respecto al testigo y a la temperatura de control. Los procesos controlados tomaron entre 2 y 13 horas más de fermentación que el testigo correspondiente. Mediante un impulsor de paletas planas, se identificó el mejor punto de operación cuando el proceso se realizó a 3 r•m-1, por 2 min, cada 6 horas. Para lograr una temperatura de fermentación en la masa de café, de acuerdo con sus características, se requiere una agitación a baja velocidad para no generar remoción mecánica de mucílago.Fermentation at a controlled temperature is proposed as a processing alternative to obtain benefits in terms of coffee quality. The changing physical characteristics in the coffee mass during fermentation become a challenge for the stirring system to achieve homogeneous temperature conditions. A fine-tuning process was carried out to determine the operating conditions of a bioreactor for fermentation in coffee with variations in rotation speed, stirring time, and the period between stirrings. Subsequently, the behavior of the fermentations was determined in a temperature range between 10 and 30 °C, at intervals of 5 °C. As a comparison for each process, spontaneous fermentation was carried out. The time to reach mucilage degradation greater than 95 % and the time to reach equilibrium between the temperatures of the coffee mass and the equipment’s water jacket were determined. The final pH was also registered. Descriptive differences observed between the processes with controlled temperature, the spontaneous fermentation in the time to reach mucilage degradation, and the final pH and temperature values. The controlled processes required between 2 and 13 hours longer fermentations than the corresponding spontaneous process. Through a flat vane impeller, the best operating point was identified when the process was performed at 3 r•min-1 for 2 min every 6 hours. Low-speed agitation is required to reduce mechanical removal of mucilage

Characterization of Fermentations with Controlled Temperature with Three Varieties of Coffee (<i>Coffea arabica</i> L.)

Temperature control is the starting point for the development of controlled fermentation and improving coffee quality. The characteristics of coffee varieties can influence fermentation behavior. To evaluate the effect of the coffee variety on the behavior of controlled fermentation and on coffee quality, a completely randomized design was used with three varieties (Castillo, Cenicafé1 and Tabi) and two control temperatures (15 and 30 °C). Spontaneous fermentation was the control for each controlled process. The fermentation time, pH, glucose and lactic acid contents, as well as, the count of mesophiles, yeasts, lactic acid bacteria (LAB) and acetic acid bacteria (AAB), were assessed. The sensory quality of the coffee was classified as very good and excellent based on the variety, with averages above 82 Specialty Coffee Association (SCA) points. The highest values were for the Cenicafé1 variety. Fermentation behaviors were similar among varieties but not based on the given condition. Compared with spontaneous fermentation, the treatment at 15 °C prolonged the degradation of mucilage in more than 24 h; additionally, there were differences in the final pH values, less than 3.5 and close to 4.0, respectively. Quality was not significantly different between the controlled fermentation and the spontaneous fermentation (Wilcoxon test p > 0.05) or between fermentation temperatures (Kruskal–Wallis test p > 0.05)