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  • Karel Schmiedberger

Rehydration of freeze-dried foods


Mandarinky před nakládáním do lyofilizátoru AMARU

While AMARU will make sure that the food is perfectly dried, the question arises as to how to return it to its original state. This time we will look at the exact opposite of freeze-drying and describe in detail how to rehydrate food.

First of all, we have to divide the food into three groups according to how it can be rehydrated:


Necessary rehydration - these are foods where the freeze-drying itself performs more of a preservation role, but the food needs to be soaked into water before it can be eaten, as it is not edible without it. Examples are lemons (you really can't eat them even if you normally eat the fresh version), eggs (without heat treatment you risk contracting salmonella) or potatoes and of course meat.

Rehydration possible - these are foods that can be eaten in a freeze-dried state and just as easily rehydrated, and they always have some use. These include most fruits, such as banana (can be eaten dry or rehydrated and used for cake, for example), mangoes and various melons.

Rehydration impossible - there are some foods that simply can't even be brought close to their original state and are meant to be eaten dry. This certainly includes any ice cream that works well as a sweet snack, but cannot be watered down and still frozen.


Rehydration is not difficult. In some cases it takes a little patience and, of course, trial and error. Probably the easiest is to restore the meat to its original state. Simply place the slices in a plate of water and each piece of meat will take back exactly as much water as needed. The effect is almost instantaneous, you can watch the ham or steak soak up the water.


The same process, only slightly longer, is the case with most vegetables and fruits. How much water each piece takes depends on its size. Here, it's also a good idea to check the rehydration status continuously, as a banana, for example, might get soggy after a long time in the water.


It's a bit more work to rehydrate yoghurt or eggs. Some people recommend using room temperature milk instead of water. There will always be lumps forming initially, especially with eggs, so you need to stir the mixture occasionally. This is also where trial and error comes in, as it is perfectly possible to rehydrate 10 eggs with water for 3 eggs. The resulting mixture will then be very concentrated in flavour, which some may find a disadvantage and some may find an advantage. Of course, it's better to start with less water and gradually add more so that you don't turn your yogurt into yogurt milk right away :)


Rehydrating ready-made and whole foods is a chapter in itself. You simply can't slap salmon with vegetables and sauce into a bowl of water. Sauces can be rehydrated separately, like yoghurt, and the finished dish should be reheated straight away when rehydrating, and a steamer is perfect for this.


In some cases, care should be taken with the brittleness of the food. For example, it probably doesn't make much sense to rehydrate potatoes in their entirety, because just running water breaks them into small pieces, and they won't retain their original firmness anyway thanks to the freeze-drying process, as the video shows:

When rehydrating food, warm water (milk) always works better than cold water. It doesn't have to be hot water directly, a temperature of around 25°C to 35°C is sufficient.


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