Freeze dried vs dehydrated foods
by WRETHAOFFGRID on FEBRUARY 21, 2011 - 19 Comments in FOOD, SELF-SUFFICIENCY, WRETHA

I have the opportunity to talk to people about storing foods from time to time, especially since we are off grid and do not use refrigeration very often, we have a couple of small dorm sized fridges but rarely plug them up, I also have access to my neighbor’s refrigerator. I have heard more than one conversation where people confuse dehydrated food with freeze dried foods. They are in fact, two different things.

dehydrated strawberries

freeze dried strawberries

What they do have in common is the food has had most of the moisture removed, where they differ is the methods that are used to dry the food, and the texture and weight of the finished product. Wikipedia says:

“Drying is a method of food preservation that works by removing water from the food, which inhibits the growth of microorganisms and hinders quality decay. Drying food using sun and wind to prevent spoilage has been practiced since ancient times. Water is usually removed by evaporation (air drying, sun drying, smoking or wind drying) but, in the case of freeze-drying, food is first frozen and then the water is removed by sublimation.”

Typically food that is dehydrated shrinks and becomes more dense, though lighter because of the water weight being removed. Foods that are freeze dried will look more like the original food, there is less shrinkage, the main difference is the texture, the freeze dried food will be lighter (in weight), less dense, and will have a light crunch if you eat it in its dehydrated state. It also returns to a more natural/original form when rehydrated.

Dehydrated food is simply food that has had its moisture reduced, period. This is something that anyone can do. Freeze dried food requires much more high end equipment. The food is frozen in the presence of a vacuum. This process causes the moisture in the food to go from a liquid state to a gaseous state, skipping the frozen state, this is called sublimation. I am simplifying this quite a bit, needless to say that most of us, the ordinary public, will not be able to freeze dry foods at home.



tumblr statistics

Tags: , , ,

19 comments

1 elnav { 02.21.11 at 6:30 pm }

Is the nutritional value the same for each kind of dehydration method?

2 Wretha { 02.21.11 at 7:16 pm }

elnav, as far as I know I would say that there would be just a little nutritional differences between the two, making an educated guess, I would suspect that the freeze dried might be slightly better because of the amount of heat applied to the dehydrated foods vs the amount of heat applied to the freeze dried foods.

Wretha

3 itwisnaeme { 02.22.11 at 5:09 am }

The temperatures used in dehydration are low enough for no “cooking” to take place, thus nutrients are preserved. Those on “raw” food diets use dehydrators all the time. What bothers me though, is the quality of the air which we pass through them – is it clean?

4 Wretha { 02.22.11 at 8:54 am }

itwisnaeme, you haven’t seen my el-cheapo food dehydrator with the melted plastic trays LOL… of course I realize that is not how it should really be done, you are right, properly done dehydrated foods shouldn’t be heated enough during processing to “cook” the food. I still believe that freeze dried foods retain a better texture and appearance, and rehydrate into a better (more original) state, but for most of us, this does not fall into a DIY category. As far as the air goes, that would depend on where you live, if you live where there is clean air, then no probs, if you live in a polluted area, then you might need to filter your air as much as possible, for your own health as well.

Wretha

5 Jean { 03.05.11 at 6:27 pm }

Hi Wretha,
First I would like to say I really enjoy your posts here and look forward to reading them.

“The food is frozen in the presence of a vacuum. This process causes the moisture in the food to go from a liquid state to a gaseous state, skipping the frozen state, this is called sublimation”

I know what I am going to write is very simplistic, but if you had a Foodsaver couldn’t you in reality vacuum pack, strawberries, then freeze them, and hopefully they would freeze dry? I haven’t got a foodsaver, or I would be in the kitchen experimenting at this very moment! Does anyone out there know why this would/wouldn’t work? Does anybody want to try to do this? Imagine the tricity you would save, not having to run the dehydrator for 14 hours at a time.
Jean

6 Wretha { 03.05.11 at 9:12 pm }

Thanks Jean, unfortunately using a vacuum pack then freezing wouldn’t work, I watched one of those “how everything is made” sort of show, it showed how foods are freeze dried, yes it is dried in a vacuum but this is done in a huge sealed room, it looked like something from NASA. They use specialized equipment that pulls the frozen moisture from the foods and collects it on these “plates”, I didn’t go into detail about that because it’s not something that most people will have the capability of doing. Believe it, I have tried thinking about how I could freeze something while I was dehydrating it and pulling a vacuum at the same time, it’s just not very likely to happen in a home situation. If you used the Foodsaver to vacuum pack something then freeze it, there is nowhere for the moisture to go inside the pack, you just end up with frozen, vacuum packed food.

Wretha

7 Mary { 03.13.11 at 1:34 pm }

Which is less expensive to buy of the two types?
Is shipping a huge cost when buying a large supply of these type foods?

8 Rohini { 04.06.11 at 5:46 am }

Which is better: dehydrated or freeze dried foods in terms of nutritional value, taste and price? Are chemicals added to freeze dried foods?

9 Wretha { 04.06.11 at 11:36 am }

Rohini, personally I prefer freeze dried, only because the process leaves the food item in a more original state when re-hydrated, it does tend to be the more expensive of the two processes, mainly because of the extra equipment required. That is not to say that dehydrated is not good, it is fine as well.

Wretha

10 Lynn { 04.09.11 at 12:53 pm }

Scientists are saying freeze dried strawberries can prevent esophogeal cancer, do you know if this is true for dehydrated strawberries as well, or is it just freeze dried? Thanks for the help

11 Max { 03.04.12 at 6:02 am }

I know this article is a year old and unlikely to garner a comment response. But I’ll ask this anyway.

You say that freeze-dried foods don’t shrink as much as dehydrated foods. But if one is concerned about the practicality of storage volume, isn’t that a bad thing? I guess what I’m asking is, is it impractical to purchase emergency supplies of freeze-dried foods (vs. dehydrated) because it takes up too much room? Or have you found the freeze-dried to still shrink enough from its original state that it’s not too bad.

12 DocV { 09.24.12 at 12:08 am }

Hey Max, freeze dried food takes more space because it retains its original shape and size, rather than shriveling up. But if space is your concern, you could always crush it. It would then still retain all the flavor and nutrition, just be a healthy tasty pile of mush.

13 Aaron { 02.01.13 at 11:23 am }

I know this has already been asked but I think it’s worth revisiting. My understanding of this process is that the food is first frozen, typically rapidly, then placed in a vacuum and the temperature is allowed to rise slightly. This allows the sublimation process to work. Couldn’t we freeze something, perhaps with the aid of dry ice in the freezer in attempt to do it faster, then use one of those vacuum containers (not a bag) with a pack of silica to absorb the moisture as its released? I know we could never get down to the temperatures that they do in the actual industry but I wonder if this would work for some things.

14 Aaron { 02.01.13 at 11:45 am }

In fact apparently you can make a flash freezing liquid solution or if du I’ve and alcohol. Then you drop in your item and vuala flash frozen. Of course use extreme caution as your fingers can freeze just as easily.

15 Aaron { 02.01.13 at 11:46 am }

*With dry ice and alcohol*

16 Peter { 05.03.13 at 2:43 pm }

@Aaron,
Freeze drying or lyophilisation, is a very time consuming process and you have to control the increase in temp so you do not exceed the rate in which you can remove the moisture. I have looked into doing this on my own and the cost quickly grows. basically you will need some liquid nitrogen, a heating pad, an air conditioner, a pressure vessel that can hold a vacuum and a pump to create and maintain said vacuum. Put it all together and presto a freeze dryer. Silica packets are a good idea but i think you would find that you need a lot to absorb the amount of moisture you are creating and the cost would quickly be more than just buying it from mountain house. you can find units for sale online for about $3000.00

17 christine paris { 02.16.14 at 3:35 am }

Here is a website that says you can freeze dry with a freezer – anyone tried it? I think I will.

18 christine paris { 02.16.14 at 3:36 am }

oops forgot the website http://www.wikihow.com/Freeze-Dry

19 Wretha { 02.16.14 at 4:23 am }

christine paris
I have my doubts, it will FREEZE the food, and it will probably get freezer burn leaving the food uncovered in the freezer for a week, the fact that they say you must store your “freeze dried” food in the freezer is a hint that this is not the same thing as commercial freeze drying, that being said, give it a try and let us know how it works for you, I’d love to hear that it worked great. :)

Wretha

Leave a Comment


Creative Commons license, which allows you to utilise all the information on this site for non-commercial purposes, providing you credit the information with the word 'off-grid.net', which should be written as one word and accompanied by a link to our web site.
View our creative commons license. View our Privacy Policy.

Vivum Intelligent Media Ltd. 2009
17 Scawfell Street
London E2 8NG

email nick (at) off-grid.net,
call US office:
toll-free 1-877-706-7423
OR
UK +44 207 729 2749