Introduction: Freeze Dry at Home

Picture of Freeze Dry at Home

In response to an Instructables thread from 2009 that I ran across, I decided to test if any idea for an at home lyophilizer (freeze dryer) could work? I didn't have a vacuum pump or any sophisticated condensing or cooling equipment. I've worked with desiccators in the lab and I thought that if I could get a vacuum chamber at the vapor point of water, I might be able to keep it under that point with anhydrous salts.

The Post:

Step 1: The Science Behind the Suck

Picture of The Science Behind the Suck

Through my research I learned two interesting facts that led me toward my final project design:

1. Freeze drying is the result of both negative pressure and temperature.The rate of drying depends on both.
2. Freezer burn, and that annoying build up of ice in the back of your freezer, are the result of the same process--namely water vapor leaving or forming solid ice. This freezer-burn vaporization is called sublimation and its opposite freezer ice buildup is called deposition.

Now this led me to think that if I could lower the pressure in a sealed container to the vapor pressure point and keep it there, I could achieve freeze dried fruit goodness in the back of my freezer.

Scientifically, the problem is vapor pressure. Vapor pressure relies on temperature and pressure. The vapor pressure of our berries will tend to equalize with the pressure and temperature inside the chamber. This means roughly that a food being passively dried will only get as dry as its environment.This makes it more difficult to dry something further. (The water keeps coming out of the fruit and raises the pressure.)

This can be solved at home by putting a desiccant in the low-pressure container to absorb the vapor and to actively pull it from the food you want to dry.

However, this means that the rate at which the vapor leaves the food and enters the desiccant is much slower than an active vacuum system (traditional vacuum lyophilzer).

After testing how much vacuum it could pull, I chose to use a wine saver hand pump for my first experiments (see picture below). There are many other similar systems on the market--usually labeled as instant marination containers or vacuum bag systems.

Step 2: Merging Materials

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(1) Vacuum chamber: VacuVin instant marinator was used. It's expensive. One can easily make their own using a ball valve and sealable container.
(1) Vacuum source: hand pumps are easily available but lower pressures can be reached using other methods.
(1) Calcium Chloride powder: use roughly double the weight of sample you wish to dry, but more can't hurt.
(1) Separation dish: this keeps the desiccant and your sample from mixing and messing up your final product.
(1) Sample you wish to freeze dry.

*When combining make sure that no desiccant gets into your food, calcium chloride is a food safe additive, but it tastes gross.
Silica gel can also be used but I haven't tried it, its more expensive and it isn't as powerful of a desiccant.

1. Prepare your sample by slicing in to thin strips or small pieces. This will make the process go faster.
2. Flash freeze the slices if possible to prevent ice nucleation and to preserve cell walls.
3. Prepare container by pouring double weight of desiccant in the bottom.
4. Place separation dish and position sample so that it is removed from the desiccant. Leave room for the desiccant to expand as it will when absorbing water.
5. Seal lid and remove air from container. The more air you remove the faster the process will go.
6. Place in a deep freezer or the coldest part of the your freezer. Lower temperature will prevent nucleation, also high sucrose solutions (ice cream) will tend to deform at temperatures over -30 C for very complicated reasons having to do with residual water acting as a plasticizer.
7. Leave in the freezer for a day and re-vacuum, then leave for around a week, or until your sample is dry. This will vary depending on the sample, the temperature, the pressure, and the desiccant.

Step 3: Making My Masion Magnificant

Picture of Making My Masion Magnificant

This is an intermediary step where a different container was prepped to accept a wine saver vacuum valve. A standard ball valve could have been used but this method was easier with the wine pump and wine saver valve.

Step 4: Delicatessen and Desiccant Decisions

Picture of Delicatessen and Desiccant Decisions

Considerations should be made when determining what you want to freeze dry. The speed and quality of drying can be hastened by making sure you follow a few guidelines:

1. Fewer samples or thinner slices work best. Cutting your samples into thin slices increases the rate at which the vapor can sublimate. Having a few samples reduces the amount of pressure lost due to water vapor sublimating.

2. Freeze fast or use a lower temperature deep freezer. The faster you can get your samples to freeze, the smaller the ice crystals will be. A good example of this is old ice cream. If given a warm freezer to recrystallize, it tends to get icy and gritty. Freezing fast will help in both sublimation and texture retention. This was my major limitation at home and why my final results looked shrived and dried around the edges.

Step 5: Water Weight

Picture of Water Weight

I wanted to include a few pictures of before and after calcium chloride. Note this is the same amount, just swollen after absorbing the water vapor from my strawberries.
Unfortunately for science I didn't weigh before and after, as I didn't have an accurate enough scale. If anyone wants to continue this experiment on their own with pressure gauges and a scale, accurate sublimation rate measurements could be determined.

Step 6: Fruits of Fruition

Picture of Fruits of Fruition

I'd like to thank you dear visitor for perusing my instructable, and I hope as a community we can continue to make food science awesome!


lperkins (author)2015-09-05

Seems simple enough... Would you need the dessicant if you just kept the vacuum source connected to draw all the water vapour out?

nathb1028 (author)lperkins2016-01-20

Yeah you can totally use a strong vacuum to pull all of the water out! the two problems with that are:

you need to have it on for a while while it removes the water actively from the food.

And two that most vacuum pumps that can do this don't take kindly to water vapor in their pistons, hence condensers are often used to bring the water back to liquid or ice before it gets in and ruins the pump.

Ecclesias (author)nathb10282017-09-21

I'm considering building this into a small freezer(craigs list or other) and using shop air and Venturi valve to overcome the power and water vapor in a pumps pistons... Viable?

kirkallie (author)2016-11-21

Great read....Would it be beneficial to dehydrate the fruit first to remove most of the moisture? Do you think this is strong enough to freeze dry coffee make instant coffee?

TonyD133 (author)2016-07-29

Hi there, thank you for sharing. I just want to make sure that I understand correctly. All I need to do is: place the fruits in a vacuum-able jar (e.g. FoodSaver) with a desiccant, vacuum all of the air out of it, and then freeze it, then vacuum again. Is it really this simple?

Also, two questions: Is the second vacuuming meant to suck the moisture out of the desiccant to allow for more thorough drying? Was the second jar you used just an extra freeze-drying medium (so you can freeze dry two different things separately)?

nathb1028 (author)TonyD1332016-08-01

So through out the process the vapor escapes the food and fills the desiccant enriched jar, the second vacuuming is meant to make sure the vapor goes away and that the water in the vapor inside does not erode your seal on your jar. As for your other question, yeah I just tried two different ways of doing it.

reauxbeauxcop (author)2016-05-03

Nice! I'm really excited to try this. Would you mind explaining how you modified the canister in the one that didn't require the marinator? What size hole, how did you drill it?


szanand (author)2016-02-03

Could I use vacuum bags instead, or it wouldn't let vapor to leave?

szanand (author)szanand2016-02-03

Sorry, just understood the process. :)
No need for answer

goldamazon (author)2016-01-17

Awesome idea since that sort of stuff is so expensive and one can't be sure what sort of quality of produce was used. I am seriously wondering if this idea could be upscaled to a huge box inside a maxed out freezer. Or multiple vacuum tubes inside of a maxed out freezer. Has anyone ever tried anything like this. Thanks for the post I really apreciate it.

nathb1028 (author)goldamazon2016-01-20

I am unsure about upscale, but I would be interested to see if anyone attempts it! To prefect the method you'd have dial in the food, pressure and desiccant that you'd use every time for consistency, something that I think would be quite difficult to do without a fair bit of experimentation and QC.

mkaddict (author)2015-10-24

Is it ok to sit the fruit on a plastic colander instead? I mean, would a plastic colander cause a chemical reaction with the calcium chloride and the fruit? I just want to be sure I'm not eating toxic fruit. Thank you!

nathb1028 (author)mkaddict2016-01-20

I had plastic containers both times for my freeze dryer chamber, a colander shouldn't be much different, I washed them out and they were spotless after a nice bout in the dishwasher. The good thing about most desiccants is that water can clean them up really easily! Calcium chloride is often added in the place of salt in some foods. However do not ingest anything that is not food grade or that you are unsure about. Do not inhale calcium chloride as it can irritate your respiratory system, and lastly don't put it on your skin as it is a mild skin irritant. Most issues with calcium chloride are due to its extreme moisture sucking and solubility capabilities.

maria.gonzalezherr (author)2014-12-06

could I use a food saver as a vacuum? would that build up enough pressure?

Yes, but you want to plumb in a check valve between the pump and the jar, you don't want to try and pump the jar for a week straight, get it to pressure and shut the machine down, let the check valve ensure you don't leak air back in when the pump is off. Not sure how big of jars they make for them, but you need 4x the size of what your drying (1 unit for the food, 2 units for the calcium chloride, and 1 unit of space for "room")

I do this by running my chamber at -60C, I spread the food thin on a tray and put it in the chamber, wait 20 minutes, then I bring in my drying pot with the calcium chloride in the bottom, drop the food from the tray into a screen colander and set that in the pot, I lock the top on and draw it down with a harbor freight pump set to 20inHg and leave it for a week. It seems to work good. I've been told I need to intermittently warm my chamber slightly so I bought some pelter devices to put in the pot and try and warm the air slightly every few hours to see if I can dry things even further

nathb1028 (author)nydiver2015-03-20

Thanks so much for this reply!

RS14 (author)2014-11-29

Good work! Just wanted to correct one thing. A phase change of a vapor to a solid is depositon. Sublimation is a phase change of a solid turning straight into a vapor.

nathb1028 (author)RS142014-11-30

Good stuff! Thanks! My first usage of sublimation was flawed I edited it.

roubadg (author)2014-06-04

this was awesome... thanks for sharing...

iamaqtpoo (author)2013-09-24

Awesome, super, excellent!!! Wow that was a great read, thank you so much!

oldmicah (author)2013-09-13

Nicely done, and thank you for the explanation. Alton Bown (of good eats) flash froze berries by rolling them around in a small cooler with chunks of dry ice to flash freeze them. And our local grocery store actually carries dry ice..... (Bwa ha ha ha ) Anyway, cool idea. Thanks for sharing!

HelmutHound (author)2013-09-12

They look like preserved rose petals! A beautiful (and tasty) ible!

nathb1028 (author)2013-09-11

Yes you can! It cakes with water and this reduces the surface area of the crystal reducing its efficiency. (Why it's sold in pellets) Simply break it up after drying it to remedy this.

As a side note: There's a pretty cool saturated calcium chlorine water fountain that reduces humidity in your house somewhere online as well.

Lectric Wizard (author)2013-09-11

Thanks for this. Just a question,I know with silica gel you can gently heat it to drive out the moisture & reuse it. Can you do the same with calcium chloride?

cathypurplegirl (author)2013-09-10

Yay for fruit and science! Good job!

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