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  • Karel Schmiedberger

Lyophilization of strawberries


Veselé české jahody firmy Hortim-International, spol. s r.o.

This year we all had to wait to self pick strawberries. Thanks to the recent frost, the season has been delayed a bit. I originally wanted to go to Kolín (city near strawberry plantations), but when the self-picking started on Friday, after half a day it was all taken out and waiting for the next, still ripening pieces. And maybe that's a good thing for AMARU, because it allows us to preserve the food we want for a time when it's not widely available.


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

So I set off in the direction of the local wholesale market and bought 6.5 kg of Czech strawberries. Maybe they are from a greenhouse, maybe from a Spanish greenhouse, but for the purpose of the test they will be enough. AMARU makes no distinction in the origin of the food.


I deliberately took an extra half-kilogram tray so that we would have about 6 kg load even after cutting off the stems and selecting the bruised or bad strawberries.


Jahody naskládané v potravinářském lyofilizátoru AMARU

I often hear the claim that people are asking for freeze-dried strawberries in their whole form, but this is economic nonsense. As we have written several times, the smaller the pieces, the better the heat transfer and faster the freeze-drying. If we left the strawberries whole, we might well have to dry them for a week before they were completely dry. That's why I cut each strawberry in half right away, and it has to be said that some of the giants were good quarters.


Freezing

6 kg of strawberries is already a considerable amount of material that needs to freeze well. That's why we set a straight 12 hours for the freezing phase on the AMARU, which later on the chart proved to be borderline. Another hour or two would have been fine.


We assume that most users will freeze separately in the freezer anyway and so AMARU will be used only for drying. Still, it is a good idea to set at least 5 hours for the freezing phase, which will stabilize the temperature of the strawberries after transport from the freezer.


Drying

We gave the strawberries a total of 35 hours in this phase. When finished, I took the largest piece off the bottom shelf to verify that it was dry in the middle as well. Still, I then found one, not even very large, piece with about 1 mm of frozen core. Maybe just an aberration, but still, it would be safer next time to set the drying time to about 37 - 40 hours at this loading weight.


Result

Apart from the one piece mentioned above, the strawberries are dry perfectly. They can be crushed to a powder, as the video below shows. Of course, we didn't let them breathe too long and they went straight into the vacuum packer.



Rehydration

Rehydrating freeze-dried strawberries is easy. Just leave in water for about 5 minutes. They can get soggy if left for a very long time. You have to take into account that the strawberries will keep their colour, but they will lose their seeds, which still fall off and remain in the bag or on the tray.


Uses

Strawberries are a perfectly versatile food for freeze-drying. They can be crisped on their own in their dried state, as well as rehydrated and used in yogurt or in a roll/cake. They are also great blended into a smooth powder.


Prášek z rozmixovaných lyofilizovaných jahod

The last mentioned method has a wide range of applications. It makes a great strawberry shake or ice cream, it can be used again in yoghurt, which is nicely coloured and strongly flavoured. It is a very interesting product for pastry chefs and cooks, because strawberry powder is a kind of coloring itself and can also be used in the production of confectionery products as a decorating or sprinkling with a simple composition: 0% E-regulators, 0% colorants, 0% preservatives, 100% strawberries with clear origin.



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