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  • Karel Schmiedberger

Lyophilization of herbs

Updated: Sep 14, 2023


Freeze-dried herbs after unloading from AMARU freeze dryer

When we test our lyophilizer, we often repeat the same foods, unless we are testing a specific product for a prospective customer. However, on the blog you will always see an article from one freeze-dryer. It probably wouldn't make sense to write seven times about freeze-dried carrots. This time, however, we're going to have a reparation with herbs that won't be lacking in sharp data and new findings.


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

Still, none of us have planting beds of herbs that produce the kilograms of the necessary loading. However, we do have a wholesale Macro and with it, frozen herbs. In order to make the load a little more varied, I loaded a total of 1.8 kg of basil in small bags, as well as 2.7 kg of a mixture of 8 herbs, which specifically means:

  • 47% parsley

  • 12% dill

  • 12% watercress

  • 10% chervil

  • 9% chives

  • 5% sorrel

  • 4% rocket

  • 1% basil

With this odd coalition, no one has yet been able to tell me what the jumble of different herbs would be good for, but for the purposes of the test it will work perfectly.

Basil (left) and mix of 8 herbs (right) before loading into AMARU freeze dryer

The herbs were finely chopped in the package, which made the job very easy. A total of 4.5 kg of herbs came out to exactly five product trays, with the layer reaching a height of 2 cm. In other words, the trays were full to the brim and it would have been difficult to dry a larger quantity. At the same time, it is worth remembering that it is not a good idea to load much less than the stated capacity of 5-7 kg, as this could damage the product.

Freezing

As the herbs were frozen, AMARU did not have much trouble with freezing. When loaded, the sensors showed a temperature of around -1°C. The required temperature of around -30°C was reached after about 8 hours of freezing.

Drying

Although the very finely chopped herbs do not have thick stems like nettles, the greater weight and thus the higher amount of water in the product obviously had an impact on the length of the freeze-drying process itself. The graph indicated that the process was complete after 34 hours of drying.

Result

Traditionally, judge for yourself in the video below. All the herbs were completely dry. Probably the result was also aided by chopping them into fine pieces, which after drying can be ground into a fine powder.

There is probably no point in restating the chapters as recovery or rehydration... On the contrary, it should be noted, every 900 g of basil (1 product tray) turned into 75 g, which means 8.3% of the original weight. In the case of the mix of 8 herbs, about 115 g remained on each tray, which corresponds to almost 13% of the original weight.

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