Plums (fresh with stone)

A grinding of soft, fresh fruit fibers and stones basically requires two different technics. The best way to comminute the fibers would be a cutting principle. For harder and more brittle samples like the kernels, impact forces are best to achieve fine grinding results. When both types of samples are mixed, it is tricky to comminute to a sample homogenous paste. Usually those types of samples with different properties would be separated and ground differently.

We ordered a kilogram of fresh plums which ware accessible for our Fritsch Application Laboratory right now. With our first trial, we used about 400 grams of plums which filled the 1,4 liters Tritan vessel (also useful for oily olives) by 2/3 of the available volume. We would guess that the volume of sample will collapse during the grinding process (so surely > 500 g of plums could be fed).

We started our trail with an SOP which was programmed to comminute for 5 seconds with 2000 rpm first; then running in intervals of 5x 1 second at maximum speed (10.000 RPM) for fine grinding.

The grinding sound was a little harsher in the beginning, because the kernels (with up to ~ 1 cm thickness) were partly ground and noisier. At the end of the trial, the grinding sound was typical and the majority of kernel fragments was comminuted < 3-4 mm length.

We proceeded grinding without SOP mode and just set max. speed for 20 seconds. After a total grinding time of 30 seconds, the trial was ended and we separated coarser particles from fine ground sample fragments by sieving with a 1 mm mesh test sieve. Photo 3 is showing an intact kernel as example, next to many of kernel fragments which were still > 1 mm large.

Surely other stone fruits with smaller kernels could be ground this way, too. When lower volumes could be ground, we recommend using the optional vario-lid.

Too big kernels should not be fed, in worst case, a very long kernel might be clamped between an indentation of the grinding vessel and block the spinning knife; or a kernel fragment would be clamped between bottom and a knife (damages on the knife are plausible). Big kernels should be pre-crushed before they would be fed. Also, hard kernels can shorten the durability of a knife.