A good roast

A good roast

The best of a cocoa bean is hidden in its kernel. During the roasting process, the flavour of the cocoa is optimally developed. Traditionally beans were roasted whole, but now the alternatives of nib and mass (liquor) roasting are available.

The latest innovation by Bühler Barth is the two-in-one drum roaster Tornado RSX. This equipment works by roasting cocoa nibs. By removing the shell before roasting the problems of fat migration, off-flavours from burning impurities and extra energy use are overcome. In addition the particles being roasted are of a more uniform size. Some operators crush the nib to make it even more uniform in size before it is roasted. As with bean roasting the possibility of roasting under high humidity means that a high microbial standard can be achieved. An added advantage with nib roasting is that poorer cocoas can sometimes be upgraded by the use of reducing sugar solutions or other treatments during roasting.

The main disadvantage of nib roasting is that it is necessary to remove the shell from unroasted beans. Bühler Barth exposes the cleaned beans to infrared radiation to enable optimal shell detachment. The top priority in all process stages is given to the principle of a high yield of pure product, and thus also in winnowing.

The Tornado

The Tornado combines convective and conductive roasting technologies in a single roasting cycle that allows optimal recipe differentiation based on end product quality. Hot air streams through the cocoa nibs can be used for faster drying, saving process energy or for improving roasting notes. The conductive process enables the traditional roasting flavor to develop and can be combined with the new process possibility of convective roasting. Thanks to this new process design, the roasting time of cocoa nibs can be significantly reduced (+/-20 per cent) with no impact on flavour and with reduced energy consumption.

Batch operation allows an almost boundless variety of different process conditions, since any required roasting time and temperature combination is possible. The roasting process can be tailored to individual cocoa varieties of any origin – for optimal flavour development and intensity of taste.

Unlike conventional roasting processes, the Tornado additionally sterilises the cocoa nibs during the roasting process. The addition of water or saturated steam during roasting sterilises the batch in a highly effective manner and thus ensures a sterile end product with a total plate count below 1000 per gram.

A newly developed STP (short-time-peak-pressure) process allows shorter retention time in the reactor and significantly reduces the specific steam consumption. Furthermore, a process configuration in which the debacterisation step is situated after the roasting process enables additional savings in steam consumption. Overall savings of up to 50 per cent for the debacterising process step can be achieved.

Specialised heat recovery systems for the drum roaster provide savings of between 15–30 per cent of the primary energy demand.

The heat recovery system consists of two main components. Firstly the heat exchanger itself, which is specially designed to suit the air volume and temperature used. Secondly, a specialised gas burner application which enables the utilisation of preheated combustion air.

The heating system operates indirectly, directing the hot air around the enclosed roasting drum. About 85 per cent of the hot air is returned to the burner system, where it is reheated.

The utilisation of the exhaust air of the roasting system for preheating the burner air is another possibility of saving energy, as this reduces energy consumption to the absolute minimum.

The heat recovery system is designed with a payback period of approximately two to three years (at 7,000 h/a production time and €3.5/kWh).

Flavour improvement
The possibility of injecting water and liquid solutions such as alkali or sugar solutions allows extensive control of the taste development of the cocoa nibs.

Even taste deficiencies of the nibs such as a smoky or hamy taste can to a certain extent be neutralised and corrected.

 

Reference:

(1) Beckett ST (1994) Industrial Chocolate Manufacture and Use, 2nd edition, London: Chapman & Hall

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