Wieland Hopfe, a certified chemist and application consultant at Fritsch, discusses the milling and sizing of cocoa beans.
Cocoa beans are grown in Indonesia, West Africa and South America and are exported worldwide.
The most important products for consumers are cocoa beverages and chocolate.
The most important characteristic trait for us is the taste.
However, before it becomes chocolate, the cocoa beans have to be roasted, peeled and cracked open.
The broken pieces of the cocoa cores evolve into 'nibs'.
These nibs are then ground to a semi-fluid cocoa mass.
For the production of cocoa powder, the mass is pressed and the pressed patty is ground.
The accrued cocoa butter is processed along with the cocoa mass into chocolate.
The comminution of the nibs has already been replicated several times in the laboratory.
For this, up until now the Mortar Mill Pulverisette 2 and the Planetary-Ball Mill Pulverisette 6 classic line have been utilised.
The cocoa butter discharges and joins the broken pieces, depending on the temperature and application of energy to a dark-brown mass.
For the production of chocolate, industrial roller plants are utilised.
The Mortar Mill Pulverisette 2 passes the energy with pressure and friction to the material to be milled.
The applied energy per time unit is much less than with a planetary ball mill, which is optimised to the maximum impact energy.
Therefore, the mortar mill no longer corresponds with the large-scale technical process.
The sample remains in the mortar mill with the surrounding temperature.
The fat is only partially squeezed from the grain and a clod-shaped mass evolves.
The consistency of the sample has to be imitated.
Here, the user must work with higher temperatures; for this, Fritsch recommends a zirconium-oxide mortar bowl and pestle.
The mortar bowl and the pestle are to be warmed inside the heating cabinet to 50C.
The retained energy is sufficient to produce a homogenous mass capable of flowing in the 10-minute process period.
With the Planetary-Ball Mill Pulverisette 6, an absolute homogenous mass can be obtained in an extremely short amount of time.
In the example, the 250ml zirconium-oxide grinding set equipped with 20mm balls was used.
A 50g weighed-in quantity produced good chocolate after two minutes.
The high application of energy influenced the sensory testing, however.
The next task was to process amounts of 2kg maximum in a manner so that it could be further processed in the experimental laboratory to a chocolate mass.
The request was to grind the nibs down to a preferably fine pourable powder.
The two first-mentioned mills can be eliminated based on the desired final product.
Therefore, the Variable-Speed-Rotor Mill Pulverisette 14 was the most suitable instrument for this task.
According to the company, 100g nibs were comminuted in less than a minute.
A 2mm sieve was used.
Looking into the open grinding chamber showed that there was still enough room for additional material.
In order to obtain the required amount of 2kg, the user either has to work batch wise or the instrument has to be equipped with the conversion kit for the comminution of large quantities.
The obtained fineness is, however, sufficient enough.
The material becomes even finer when sieved through a 2mm sieve.
A comminution by using the 1mm sieve is unsuccessful.
Tests to additionally increase the fineness by mixing with dry ice were not carried out.
This would be a promising approach, however, to obtain an even finer, pourable powder in this manner.
