Fermentation is a necessary step in the processing of cacao for chocolate (Sukha and Seguine, 2015). Fermentation of the mucilage-covered beans is initiated by naturally present microorganisms such as yeasts, acetic and lactic acid forming bacteria on the pods and in the environment (Moreira et al., 2013). Typically microbial isolates are not used. During fermentation, beans begin the process of germination resulting in the conversion of storage compounds in the beans to fuel and structural components for growth. Heat and acids produced by microorganisms kill the embryo before the radical emerges. When the fermented beans are roasted, the flavor compounds associated with chocolate are produced (Schwan and Wheals, 2004).
Breeding and variety evaluation programs should ferment beans for sensory analysis of the qualitative attributes (Clapperton et al., 1994). Frequently, only small quantities of beans are available from such plots. Rohan (1963) developed the standard method for microfermentation of cacao. It involves removing fresh beans from 1 to 15 pods, which are placed in mesh bags. The mesh bags are then embedded into 100–1000 kg of beans in wooden commercial fermentation boxes. The fermenting beans are mixed (turned) aiding homogenization and aeration that encourage aerobic microorganisms. The embedded bags of beans are removed and manipulated to mix the beans inside, then re-embedded into the fermenting beans. Fermentation takes 6–7 d. The beans in the mesh bags are then dried for further processing and evaluation (Sukha et al., 2008).
Nonembedded microfermentation methods were developed when embedding the beans of interest into a commercial-sized, fermenting batch was not feasible or appropriate (Kuman and Hollywood, 2010; MacLean, 1950; Quesnel and Lopez, 1975; Seguine et al., 2013). These nonembedded methods are particularly useful for investigations of fermentation variables, such as degree of pod maturity, different locations, temperature, and microorganisms; embedding beans into a large fermentation batch confounds or prevents this.
Our initial microfermentation efforts were not satisfactory. Microfermentation was first attempted with a bread yeast inoculum and an incubator set at 35 °C for 3 d, followed by 45 °C for 3 d then stopped by removing the samples from the incubator (Bittenbender and Kling, 2009). The bread yeast produced an unacceptable bready aroma in the dried beans and resulting chocolate. Later, modular fermenters (10-cm-diameter × 23-cm-long acrylic tubes and disks) were made and used. These could ferment bean batch weights from 60 to 900 g (Gautz, 2009). Unfortunately, the fermenting vessels leaked, it was time consuming to prevent leakage, and they could not hold more than 900 g.
Neither the standard nor nonembedded microfermentation methods were suitable for our needs. The standard method required a minimum fermenting batch weight of 100 kg, which is much greater than what was available. Alternatively, the nonimbedded microfermentation methods were constrained by fermenter size, the need for prepared inoculum, sun drying, and manual temperature control, which added additional labor and material cost.
The objective of the current project was to develop a microfermentation system that did not require embedding samples in a commercial size fermenting batch, was flexible with regards to weight and number of samples, did not require prepared inoculum, did not require sun drying, and was repeatable with regard to the degree of fermentation and cocoa liquor quality. Those efforts evolved into the CTAHR CBS.
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