Is it possible to freeze dry at home?

I want to make freeze dried yogurt bites. Am I spinning my wheels?

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Dry ice with a chamber vacuum sealer should be capable... but I'm not sure if chamber vacuum sealers are rated for this sort of thing. The general requirement, though, is a VERY cold medium (dry ice, liquid nitrogen, etc.) to freeze the food and then a strong vacuum to sublimate the water out. If you don't have the strong vacuum, my assumption is that you're out of luck.

lfmichaud

The cheapest solution that I found for something new is

http://harvestright.com/store/freeze-dryer-black.html

You can also look around on ebay to try to find something really cheap if you're good with mechanical stuff. I've seen some peoples suggesting putting stuff in an open tray in a an empty freezer but I'm not convinced. But keep us informed if you work something out. Because for now on my side I'm stopping at the centrifuge... ;-)

Pepijn_31744

I'm not convinced the freezer thing would work either. However, it might be an interesting to experimenting with. If you have some extra freezer space, which -sadly- I have none, you could always give it a shot. For science. Definitely the cheapest option. As long as you don't expect any results I see no reason, beyond wasting your time, not to do it.

Brendan_Lee_56950

Isn't the point of rapidly freezing it to force it to sublimate? Otherwise you aren't really freeze drying I don't think

Pepijn_31744

I thought the sublimation happened due to the low pressure causing the water to change from solid to gaseous state at the low temperature.

Brendan_Lee_56950

right, but i think that being freezer frozen isn't sufficient for that, which is why something like LN is needed

Pepijn_31744

If I understand this graph correctly keeping the product at LN temperatures or even dry ice temperatures would require a much higher level of vacuum to get the ice to sublime. Sublimation seems to happen at temperatures as high as -1 C

Brendan_Lee_56950

How i was explained freeze drying is that you want the product to be as cold as you can get it for preserving the flavor and thus a big powerful vacuum to make it happen, which is also why I think it's pretty limited for the home user without commercial equipment. I think Heston explained it in one of the ISOP shows actually.

DiggingDogFarm_65362

https://www.youtube.com/watch?v=1qckdVa_UF4

Tim_Roth_78505

Freezing with dry ice or LN2 will accelerate the freezing process (faster rate of cooling), thus preventing the formation of larger ice crystals that can adversely affect the texture of a lot of foods (such as fruit or other plant material). Higher vacuums should allow for faster sublimation rates given that a lower temperature will lead to vaporization of the ice. A low-temp treatment with high-vacuum is basically the ideal scenario for most food applications. Foods like yogurt probably won't require the low temp step as much, but note that the freezer method will occur at atmospheric pressure, which is 101,325 Pa (See this page for a more detailed version of Pepijn's graph). Given that a standard freezer will be in the vicinity of ~253K (-20 degrees C). This will put you well above the triple point below which sublimation will occur. So in this case, you won't actually freeze-dry through any significant amount of sublimation (or at least, it will happen very very slowly - though I'll admit that I don't know enough to say that it won't occur at all).

To summarize the chart: sublimation will occur starting at temperatures below 273.16K (0.16 degrees C) ONLY below pressures of 611.657 Pa (which is much lower than atmospheric pressure). Rapid freezing prevents damaging the product and isn't a strict requirement, but you'll definitely need the vacuum.

EDIT: turns out I'm mistaken about the freezer not allowing freeze-drying. Freezer burn is cited as being the result of sublimation - although I think it's still a bit different from what you actually want to achieve given that it's a slower process. See here for more info: http://onlinelibrary.wiley.com/doi/10.1111/j.1541-4329.2009.00072.x/pdf

Mike_Minh_Truong_54120

Cool experiment.

My brother, Cang Truong, owns a Tutti Frutti franchise in Florida. It's a frozen yogurt shop and they sell freeze dried products on the side. It is cool stuff and definitely worth the effort!