Batch insert micro fermentations

This technique can be used to ferment samples of beans contained within a mesh bag (also referred to as a “net” bag) within a larger fermentation mass. The size of the mesh bag can be adapted according to the amount of beans available, and the technique has been used successfully for samples ranging from approximately 200g to 3000g, though samples of approximately 750g to 1000g are typical.

It is important to keep the surface area to volume ratio of the fermentation mass constant and this can be achieved with heaps, baskets or fermentation boxes of at least 50 kg capacity. 

Baskets made of woven rattan with dimensions of approximately 38-50 cm diameter by 48 cm deep, can be used for this purpose. 

Good results have also been obtained using inverted plastic laundry baskets of similar dimensions which have had their bases removed and been strengthened with rattan hoops. 

Fermentation boxes 60 x 60 x 60 cm (170 kg capacity) or 90 x 90 x 90 cm (600 – 800 kg capacity) can also be used.

These should be made of suitable non- resinous, hardwood with slats with gaps large enough to allow drainage of the fermentation exudates (known as “sweatings”) whilst small enough to prevent beans from passing through.

The bean sample for evaluation must be placed in labelled bags, made of an inert material such as nylon or polyethylene with no metal parts, and are of approximate size 20 x 35 cm to allow a layer 2-3 beans thick when spread flat in the fermentation box. 

A mesh size opening of 10 mm allows good contact between the sample and the fermentation mass and the thread diameter should be 0.7 mm or greater for strength. 

As a cautionary point, there could be a risk of flavour transfer from the fermenting mass to the micro fermentation in the mesh bag. 

This possible fermenting mass effect could be overcome by using similar varieties for the fermenting mass as the sample in the mesh bag and/or by using a finer (<10 mm) mesh size opening.

It is important that each mesh bag is not overfilled and that there is enough spare capacity to allow the bag to be held at each end to facilitate turning. The label on each mesh bag must contain information relevant to the sample such as (but not limited to) the clone name, the date of the start of fermentation etc.

Mesh bags should be buried in the top 15–30cm of the fermenting mass ensuring that each bag is at least 5 cm from the wall of the box and separated from other bags by at least 3 cm. 

A maximum of two layers of bags, with four bags per layer, can be included but there must be at least 3 cm of fermentation mass between the layers and the top layer must be covered by at least 5 cm of beans. The top of the fermentation must be covered by at least two layers of banana leaves and then two layers of food grade jute bags for insulation.

The first turning is done after 48 hours by removing the jute bags and leaves, then transferring the top of fermentation mass into a food grade plastic box or bucket. 

Each layer of fermentation mass and mesh bags as well as the bottom layer of the fermentation mass are placed into separate plastic boxes or buckets and are thoroughly mixed. 

The beans in the mesh bags are mixed by holding the ends of individual bags in each hand, shaking them from left to right a few times. 

The layers of beans and mesh bags are replaced in reverse order so that the top layer moves to the bottom and the bottom layer is at the top, whilst the central layer remains in its original place, and the mass is re-covered with the banana leaves and jute bags. 

The second turning is done after 96 hours by repeating the process and the optimal end point determined by visual assessment of the beans as described above.