Does Drying Method really matter?

Aveena Ramroop, 2015.

Edited by Dr. Marissa Moses and Dr. Lambert Motilal (Cocoa Research Centre, The UWI St. Augustine Campus) of a Paper presented at the International Fine Cocoa Innovation Centre Conference & Symposium, Trinidad and Tobago, March 23-24, 2015.

While roasting cocoa beans in the hot tropical sun may seem exotic to some, it is a time and labour limiting step which makes the entire process inefficient.

As part of the cocoa processing method, cocoa beans are dried before packaging. Drying reduces moisture content to a safe level (6-8% w.b.) so the bean can be stored, sold and transported. Additionally, drying is a continuation of the oxidative stage of fermentation and helps reduce astringency, bitterness and acidity. Drying cannot be too slow as this leads to the mouldy beans. However, beans that are dried too quickly may result in acidic beans where shells become brittle or the bean case hardens. In the Caribbean, cocoa is dried using special drying houses with a movable roof (Figure 1). While roasting cocoa beans in the hot tropical sun may seem exotic to some, it is a time and labour limiting step which makes the entire process inefficient. Currently, there are 24-hour mechanised drying methods which are available for other foods, and perhaps these methods could be adapted for use in cocoa processing.

In this series of experiments, three methods of cocoa drying were investigated ie. sun, greenhouse and a mechanical oven. Both constant drying and intermittent drying were also evaluated during the mechanical oven treatment. The time taken to achieve a moisture content of 8% was evaluated at 40°C, 50°C and 60°C for the different drying methods. The effect of bean depth (single layer, 1” and 1.75”) during the mechanical oven drying treatment was also evaluated. To ensure that the drying method did not reduce quality, pH was recorded, and liquor assessments were conducted.

As could be expected the rate of decrease of moisture content increased with increasing temperature during the mechanical oven trial. At 50°C for instance, it took 23 hours for the beans to achieve moisture content (MC) of 8%, as opposed to the 47 hours needed at 40°C temperature. Beans dried intermittently took triple the time to reach 8% MC, and produced more acidic beans when compared to the beans dried continuously at the same temperature. In contrast, sun dried samples took 3.5 days to reach the recommended MC while greenhouse samples took just over 6 days. The latter two methods however generated less acidic beans than the oven dried, which is preferred, except at 50°C, which is in congruence with earlier work. In terms of liquor scores (Table 1) the greenhouse samples produced poor scores when compared to the other drying treatments.

Beans dried continuously at 50˚C in a single layer were the least acidic, had a moderate cocoa flavour and took less than a day to reach the recommended MC. This indicates that continuous drying in a single layer is a favourable option for a mechanized drying procedure in cocoa processing. However, drying in a single layer would only be able to accommodate small quantities of beans and may not be a feasible option for large cocoa farms. Increasing the bean depth to 1” or 1.75”, while increasing time to recommended MC by almost three additional days, however produced liquors of high cocoa flavour and low acidity, astringency and bitterness (Table 1) as compared to the other two drying methods.

Figure 1. In the Caribbean, cocoa is dried using special drying houses with a movable roof

Figure 1. In the Caribbean, cocoa is dried using special drying houses with a movable roof

Effects of drying

Cocoa Liquor Attributes Drying method
Oven, single layer at 50°C Oven, 1″ layer at 50°C Oven 1.75″ layer at 50°C Sun Green house
Cocoa Flavour 5.5 5.9 5.9 5.0 4.3
Total Acidity 2.4 2.3 2.4 2.9 2.9
Bitterness 5.1 4.9 4.9 5.3 5.6
Astringency 6.9 6.5 6.9 7.4 7.7

To read more on these studies we recommend:

  1. de Brito, Edy S., Nelson H. Pezoa García, M. I. Gallão, Angelo L. Cortelazzo, Pedro S. Fevereiro, and Marcia R. Braga. (2001) “Structural and chemical changes in cocoa (Theobroma cacao L) during fermentation, drying and roasting.” Journal of the Science of Food and Agriculture 81, no. 2: 281-288.
  2. Hii, C. L., C. L. Law, and M. Cloke. (1990) “Modeling using a new thin layer drying model and product quality of cocoa.” Journal of Food Engineering 90, no. 2: 191-198.