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  • Karel Schmiedberger

Lyophilization of blueberries


Freeze-dried blueberries

After a short break we have prepared something new for our AMARU freeze dryer. We have already tried raspberries, for example, but blueberries usually form a precise ball without a hole in the inside of the fruit where the water could escape.

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

Because we combined the freeze-drying of blueberries with the product of one of our AMARU candidates, not all of the capacity was used, but only 4 of the 5 product trays. Even so, the machine comfortably held 5 kg of frozen blueberries.

Choosing just frozen blueberries proved to be economically economical (the fresh version would have cost many times more), but with one disadvantage. A large part of the blueberries were squashed. This is why so much juice spilled out onto the produce trays and why the blueberries stick even after drying (see below). In the case of the fresh version, the characteristics are more like corn, which did not stick at all.


Freezing

As this was a frozen version, the time to reduce the temperature to about -25°C was shorter than usual. Even though we left the blueberries at room temperature for a few hours before loading. We went from -1°C when loading to the required -28°C in about 8 hours.

If we had harvested our own blueberries on trays in a countertop freezer (i.e. -18°C), the freezing phase in the freeze-drier would have taken only a few hours.

Drying

I was a little worried about the skin, which normally prevents a quick drying process and in other fruits can be removed or at least disturbed by cutting. However, water always finds a way and 5 kg of blueberries (+ 0.5 kg of test product) were dried in 29 hours.

Result

More or less corresponds to what is loaded into the freeze-drier. In this case, many blueberries were more or less dented, but there were still plenty of intact ones. However, we can dream about sprinkling a handful of berries.

The spilt juice from frozen blueberries has such a good binding effect that after packing we got a blueberry brick. When dry, it was easy to cut with a knife.

Rehydration

Just as well as the water left the blueberries it gets back. In our case, rehydration is almost necessary because it was impossible to get the individual berries back out of the glued blueberry mass when dry.

A dried blueberry brick
A dried blueberry brick can be sliced with a knife. Maybe we could use that, too.

Blueberries take about 10 minutes to rehydrate. They only take back as much water as they need, so there is no risk of getting soaked.

Uses

If fresh blueberries pass through freeze-drying without significant damage to the individual berries, they can be added to dishes and used for decorative purposes, e.g. cakes. Our frozen - sticky blueberries are still suitable for baking, preparing drinks or blending into a dark purple powder, which offers another range of uses.

Update (9.9.2018)

Purely for completeness, if you use fresh blueberries, or at least ones that are not half crushed, you can achieve excellent results, as the video below shows:


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