We've already freeze-dried yogurt once. At that time it was a load test in a prototype, where we loaded a whole 10 kg of white yoghurt and started the process. It ended up taking about 3 days, not counting the time needed to get such a load of liquid product to freeze well.
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
This time I was looking to replenish my own supplies, so I headed to Okrouhlice to the BioVavrinec farm, whose products I have grown to like immensely. In addition to a portable fridge full of dairy products, I also took five buckets of white yoghurt, each 1 kg.
Loading was therefore very easy - each product tray came with exactly one kilo of yoghurt. Of course, the key is to create a continuous layer covering the entire bottom of the tray, trying not to make some areas thicker than others.
Freezing
I set the freezing time to 12 hours. The chart then showed that maybe an hour less was enough. The yoghurt was about 17°C when I loaded it, because it no longer fit in my auto fridge. So that made the freezing process a bit longer.
In practice, of course, it would have made more sense to have a second set of trays and freeze the yogurt in the box while the previous batch was drying in the freeze dryer.
Drying
I set the drying time to the now almost usual 35 hours. I'd eventually describe this as too much and another, identical load would be worth trying with a shorter time, e.g. 2 hours. If the product is not fully dried (it is cold to the touch), it can be safely returned to AMARU and run the drying function.
Result
After freeze-drying, the yoghurt forms a texture somewhat similar to milk. Due to the length of the drying process, the entire layer of dry yoghurt peeled off the product trays. As the video shows, it can simply be ground into a powder.
Rehydration
Yoghurt is one of the foods that we are unlikely to eat dry, but it can easily be returned to its original form before freeze-drying. All you need is a little water or milk. The advantage here is that you can add the water gradually and thus de facto choose the density of the yoghurt you want.
Uses
Interesting is the weight loss - the original 1 kg of yoghurt after drying was exactly 150 g. I store the freeze-dried yoghurt myself at home so that I do not have to buy it all the time. As long as the vacuum in the bag is not broken, yoghurt can last for many years and still be the same as the yoghurt you just bought after rehydration.
However, the curious person will also come up with other possibilities. A sprinkling of white yoghurt on cakes or desserts could be interesting - a thin layer would make the yoghurt melt on the tongue. It can also be combined with freeze-dried fruit (strawberries, banana, etc.) and packaged as an instant yet healthy snack.
