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Dry Freezing. Answered

 Can you dry freeze something when its a liquid?  
 could you take a liquid solution and submerse it in dry ice to dry freeze it?



7 years ago

i have a question. There are a ton of eHow instructions on "freeze drying" that are just plain wrong. they leave no avenue for water to escape. They suggest putting food in freezer bags and then putting those bags in dry ice. Well won't that just freeze them but not dry them.

Anyway, this is my queries.
Freeze dry happens because you first freeze the water. Then Displace the water by sublimation. But this sublimation can only happen while the water is frozen and in negative pressure. If I wanted to do this to say,blackberries, if I freeze them normally they will crystalize and become mushy. So wouldn't I just flash freeze them with the dry ice to start?

Second. If I have dry ice flash frozen blackberries, could I then put them into a canning jar, (i suppose I'd have to keep the canning jar in the dry ice to keep the contents cold) and could I use my Foodsaver jar attachment to draw the vacuum? I use this attachment on canning jars and it draws out the air in the jar enough to make the rubber lid stay tightly because of the vacuum. But there would me only a vacuum no CO2 gas in the jar.

Do you think that would work?
Your chitosan bandage instructable step 5 doesn't use a vacuum. just the container with a small hole. would that work for letting water vapor out? I wanna try this to make cat treats and freeze dry herbs, berries and other weird fun stuff.

Hmmm... Have you tried sublimating any type of food before? I havn't tried fruit but I did throw a slab of ice cream on the side of my projects. With chitosan bandages the vinegar solution is frozen and then later displaced into a gas leaving only the wanted ingredients. The process of sublimation is a transition from a solid DIRECTLY to a gas. In order to sublimate properly, you must first freeze your blackberries (or other choice of fruit) to make the water inside into a solid. When you freeze them the first time, place them in an airtight container or bag to reduce condensation and crystallization of the contents. An important thing to remember is that with cold temperature comes low pressures. The dry freezing container must be airtight to ensure both of these important factors. The pressure should be low enough that you wouldn't have to use a vaccuum. The best idea I have to freeze dry blackberries would be to first freeze them, and then place them into my dry ice bin. (be sure to open the bag in the dry ice bin to allow gas to escape.

Oh, I see. So the first time i freeze them they should be in an air tight bag, but during the sublimation, they should be exposed so the gas can push out the frozen water.

You make things make so much sense!!

I forgot about low temperature making it's own low pressure area! I'm so glad you clarified that for me.

I've never purposely sublimated anything, but my cat sure loved the chewy tilapia filets that got freeze dried in my friends frost free fridge cause she left the bag open. I hope to duplicate that on purpose. Thanks again for the response. I'll go reread your instructable for the details!

Good luck and let me know how it goes! You could even post an instructable on freeze dried tilapia filets!

 I think you might have a different understanding of what dry freezing is.  It is a process usually done to food to "dehydrate" it, removing the water liquid quickly so you end up with some powder or dry block of something.  There are dehydrated soup mixes.

You might want to look up cryogenic techniques to cool liquids rapidly.  Besides, dry ice is in block or powder form so you are mixing it with the liquid to be cooled. You get that cool bubbling fog effect when they come in contact.

 Thats what I want to do..I want to "powderize" a solution from liquid. I have heard that you have to freeze the solution first but I want to know if it can be done while its still a liquid.

 Depending on what the liquid is, it still seems you need some heavy duty industrial equipment to do it.  But that never stopped anyone from trying.  Good luck.

I figured it out.. It can be done with enough dry ice. If you want to check out my instructable just type in how to make chitosan bandages. Thanks for you help!

You could do tiny bits at a time like a spoonful, with a bucket of dry ice and some clever shaping...  

Freeze-drying involves freezing (the water content), then evaporating it by sublimationunder reduced pressure, such that the ice doesn't melt while it's evaporating. For large volumes you need repeat-cycles.
The advantage is not heating the material too much.

What do you want drying?