Solubilisation (alkalising)

Objective

Solubilisation (or alkalising) is the neutralisation of cocoa nibs or cocoa liquor with an alkaline solution, resulting in a darker colour and a milder taste. The milder taste is mainly the result of the neutralisation of the light acidity of fermented beans. Considerable experience and skill is required to obtain end-products with a constant colour and hue.

Field of application

Solubilisation is used primarily in cocoa processing.

Description of techniques, methods and equipment

The process is carried out by adding an alkali solution, usually potassium carbonate (K₂CO₃), to the cocoa. Two different methods can be applied:

a) Liquid process

Processing the liquid cocoa liquor allows the opportunity to modify the flavour. Potash solution is added to the liquor until a pH value of 7 to 8 is achieved. The desired solubility is obtained by increasing the temperature from 45°C up to 130°C. Water vapour and undesirable volatile components are released to the atmosphere during the heating phase.

b) Nibs alkalising

Processing green or pre-dried nibs has the advantage of combining the drying with the nibs roasting. A disadvantage though is the presence of the cocoa butter in the nibs, which may result in slight damage to the fat. Batch and continuous processes are available. Batch processes consist of a solubilisation tank at atmospheric pressure with a high shear impeller. Continuous processes take place in a reactor followed by a mixing tank, usually under vacuum. A typical batch alkalising process involves two steps. Firstly, the nibs are neutralised by adding the alkaline solution in a reactive vessel at atmospheric pressure. The reaction takes place within a temperature range of 80°C to 105°C. In the second step, water evaporation and nibs roasting are carried out in a fluidised bed dryer.

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