With the summer holidays always comes the time of cherry harvest. And since there are more and more questions about the possibility of freeze-drying various stone fruits and berries in whole, I decided to enrich the usual test this time to see if it is possible to dry these foods in whole.
As we said in an earlier article, it is always better to cut up the load or ideally to blend it straight. The smaller the pieces, the greater the surface area for draining the product and thus the faster the drying. Cherries then are at that limit where it is a small fruit, but this one already has a stone that cannot be eaten (it has to go), as is the case with gooseberries. In other words, pitting is much more labour-intensive than for apricots, for example.
I loaded the freeze-drier with 1 kg of cherries with stone but without stem, 1 kg of cherries with stone and stem, where I made 3-4 holes with a 1 mm needle and the rest was filled with pitted cherries.
Note: This test was performed on an earlier model of the AMARU lyophilizer. We have made several improvements since then and today the capacity would be higher and the process faster.
Preparation
As already mentioned, pitting cherries in manual mode is not easy. Fortunately, there are technologies that can help a little. De-stemmers can be found today for as little as about €5. For the purpose of processing a few kilograms, we opted for the proven quality brand Tescoma, which came out to around EUR 20. If you plan to process larger quantities of cherries, I definitely recommend watching the video:
Of course, nothing is as rosy as advertising. Sometimes the cherry gets stuck in the cartridge and needs to be ejected. Other times, the cherries in the tray can't agree which one will go next and need to be helped again. However, compared to hand-picking, the ease is noticeable.
Freezing
When setting the freezing time, I slightly underestimated the tray, which didn't even weigh 5kg but contained two shelves of whole, uncut cherries. The temperature eventually managed to drop to the necessary -25°C thanks to the vacuum, but the ideal time for this kind of loading (larger, undisturbed pieces of fruit) would be about 15 hours of freezing.
Drying
The drying phase was set at 35 hours. However, after this time, we found that it was not yet done. The pressure was only at 380 mTorr and it only makes sense to pull the product out at around 200 mTorr.
A liner consisting of completely pitted cherries would have been ready by this time, but it was some of the whole cherries that were obviously preventing the water from draining and being trapped as ice on the chamber walls.
Result
Rather than go into a long discussion, the video will tell the whole story:
It is also worth adding that each kilogram of cherries yielded 850 g of pitted cherries, of which approximately 140 g remained after drying. That is, 16,4% of the original weight of the load.
Uses
The pitted and well-dried cherries can be ground into a powder. In addition, they can be rehydrated. This does not give you "just-picked" cherries, but is perfectly adequate for use in the kitchen.