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  • Karel Schmiedberger

How long does it take to freeze-dry food

09/2020 - Article updated with results from AMARU with new cooling unit.

Dotyková řídící jednotka lyofilizátoru AMARU

If AMARU were a kitchen device, it probably wouldn't be a major issue. But because we make equipment for small business, time means money and therefore the question of the duration of a process is spot on.

Right at the outset, it's good to state that there is no single time that will always apply to every type of food. Just as with a washing machine it makes a difference whether it washes one T-shirt or 7 kg of laundry, with a freeze dryer it depends on the quantity and type of food being dried.

In AMARU, the whole process is divided into 2 parts - freezing and drying. The first one can have more than one form. It depends if the freezing of the product is done by AMARU or if the user decides to save the machine time of the freeze dryer and freeze the product on trays, for example in a storage freezer.

Freezing phase (in AMARU)

When 5 - 7 kg of food is loaded into the AMARU, it usually takes 15 - 20 hours before the product is well frozen. Of course, it depends on whether it is, for example, milk at room temperature or ice cream, which is already at around -4°C.

Assuming that the user will frequently freeze the same products, it is best to check the correct freezing. Simply interrupt the program for the first few processes, open the chamber door and use a needle thermometer to measure the product at various points in the chamber. You can then be sure that you always set a verified freezing time.

Freezing phase (in the freezer)

Freezing the product in the freezer has the advantage of saving time - in AMARU, one batch can be drying while the other is already freezing. Again, it is a good idea to check the temperature of the product before loading it into the freeze dryer. Remember that even a short transfer of trays across one room will heat the product considerably and therefore it is necessary to set at least 5 - 7 hours of freezing time in the AMARU for stabilisation.

The above applies if you have a freezer up to -20°C or more. While a standard freezer (about -12°C to -18°C) will help speed up the freezing process, you will need to set a longer freezing time once you have put it in the freeze dryer. The product should be around -25°C when drying starts.

Drying phase

The average time for the freeze-drying process itself is about 30 hours. Thus, a product that takes up all the shelves but does not have a large weight (herbs, ice cream,...) will dry for 24 hours or less. By contrast, an 8 kg liquid product (yoghurt, eggs,...) will take 40 hours. The more product you put into the AMARU, the longer the drying time will be. When we dried 10 kg of yoghurt, it took less than 45 hours.

To summarise: freezing takes 15-18 hours, but can be reduced to about 5-7 hours by using a suitable storage freezer. Drying is then a matter of 30 hours on average, depending on the type and quantity of loading.


Therefore, if the freezing and storage schedule is well optimised before drying in the freezer, the process itself can be a matter of one and a quarter days.

 

Do you want to be sure? Contact us and together we will test the lyophilization of your product.


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