Chocolate

A general statement for a proper sieve ring is not possible. The composition of the chocolate is extremely influencing the possible grinding results. Usually, the higher content of fat is requiring an embrittlement of sample before a comminution to powder is possible. Without embrittlement, samples will just melt and smear into the trapezoidal openings of the used sieve ring.

With our first trial, we used dark chocolate which was made of 85 % cocoa beans. By hand, we broke the sheet of 25 into pieces of ~ 15 mm max. The pre crushed pieces have been placed into a basin which was filled with liquid nitrogen. Rapidly, the chocolate was brittle enough to be fed and ground.

We fed the complete sample with a sieve ring of 1,0 mm trapezoidal perforation. Feeding took about 35 seconds; grinding sound vanished instantly after the last piece got fed.

The rotor ribs are coated with chocolate; the openings of the sieve ring are mainly free. Even higher amounts of sample can be ground this way. Fine powder was sticking to the collecting pan. For an intensive cleaning, we recommend to was off residues with hot water.

Next to 1,0 mm sieve ring, also two further trials have been performed. Sieve rings of 0,75 mm trapezoidal perforation as well as 0,5 mm trapezoidal perforation has been used with smaller quantities of sample. With just 5 grams of embrittled sample, about 30-40 % of the perforations of the used 0,75 mm sieve ring have been already clogged with chocolate. With 0,5 mm sieve ring, a change in grinding sound indicated that all openings have been closed right after 2 grams of sample got fed.

Most tricky might be easy to melt milk chocolate with / or without hazelnuts. A first test with 1,0 mm trapezoidal perforated sieve ring has shown that those small openings are clogged rapidly.

With this test, we used a sieve ring of 2,0 mm trapezoidal perforation for comminution. Sample with up to 1,5 cm length got embrittled for about one minute and was fed spoon wise to the feeding funnel.

After ~ 50 seconds, all 25 grams have been fed and ground. After comminution, the rotor ribs are completely free of residues. Melted sample is sticking to the outside of the used 2,0 mm sieve ring.

We estimate that even higher amounts of sample can be ground this way.

Also the premium line model of Variable Speed Rotor Mill PULVERISETTE 14 has been used to testify grindability. With the rest of milk chocolate sample which included the hazelnuts has been used analogue result 2. This time, a 1,5 mm sieve ring has been test.

The pre crushed and embrittled sample was fed slowly. Within 45 seconds, the 20 grams of embrittled sample has been ground. Also this kind of chocolate was ground successfully. On the outside of the used sieve ring, again melted chocolate could be found.

To testify the difference in comminution with lower speed settings, we used the Variable Speed Rotor Mill PULVERISETTE 14 and reduced its rotor speed to 12.000 rpm instead of 20.000 rpm.

We fed 20 grams of milk chocolate to the machine for comminution with 2,0 mm sieve ring.

After 80 seconds, all sample has been fed. While rotor was completely free of residues at maximum speed, now the rotor is covered with sample dust. Instead of melted particles on the sieve ring, now the sieve ring is way cleaner compared to result 2. It needs to be figured out for each kind of chocolate which speed setting combined with which sieve ring perforation uses to be the optimum.

For finest results without sticking of particles, we recommend choosing a grinding method which has direct contact of liquid nitrogen with sample. Therefore, only Mortar Grinder PULVERISETTE 2 (with monolithical stainless steel mortar and pestle) or Vibratory Micro Mill PULVERISETTE 0 (for smaller sample amounts) will come into question.

We prepared 20 grams of sample; pre crushing is not required that fine; we used particles of 2 cm length and placed left and right to the 50 mm Ø grinding ball.

In the beginning of the grinding process, higher amounts of nitrogen are required to chill the grinding set and sample. After a few minutes of comminution, only small amounts of liquid nitrogen needs to be filled into the feeding funnel to replace evaporated nitrogen.

We interrupted the grinding process after 2 minutes of grinding. When nitrogen is evaporating, fine particles get lightly compressed by the grinding ball. After sample reached room temperature again, few particles stick lightly together.