The very last of the output tests of each AMARU freeze dryer is so-called "24/24 test". We test all components, some of them repeatedly, but this test is to verify that the AMARU is working as it should in the activity it was designed for. It is named after the process settings, i.e. 24 hours of freezing and 24 hours of drying.
While 24 hours of pure water freezing is an oversized value that is only meant to completely eliminate the possibility of insufficient freezing of the product, 24 hours of drying is the limiting value for drying a given amount of water. The amount varies whether the AMARU is equipped with 5 or 7 shelves, but this always verifies that the promised drying rate is guaranteed to the customer.
However, in one of our last tests we did not dry everything. After the freeze drying process was complete, we pulled some trays containing a few pieces of ice out of the chamber, always at the back of the product tray.
At first I was taken aback and wondered what could be wrong with this AMARU. However, Pavel repeated the test and everything was now completely dry and the test was therefore successfully completed. What was the crucial difference?
I had made a mistake. When I moved the AMARU into the test room, I used a spirit level to ensure that the product trays were level in both the X and Y axis. However, I settled for the bubble of the spirit level being between the lines, not noticing that it was almost on one line and not exactly in the middle.
Certainly, if a customer were freeze-drying herbs, meat, fruit or vegetables, it would not have much effect. However, even such a small difference in balance will make a difference with liquid products. The liquid simply moves to one edge of the product tray and creates a thicker layer that takes that much longer to dry. The difference can end up being several hours longer drying process.
The same is true, of course, if you are freezing food on trays in a freezer. There, on the other hand, the freeze-dryer itself does not need to be in an exact level, because the product is loaded frozen and there is no possibility of it moving around on the tray. Nevertheless, it is advisable to keep the AMARU in a plane, which is why it is also equipped with adjustable feet.