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The dehydrator can dry many foods, but there are certain ones that don't work well. A freeze dryer can dry those foods, but it is a more complex process. These foods include strawberries, blackberries and raspberries, and a few others which simply do better freeze dried instead of dehydrated.
A dehydrator shrinks the foods when drying them. The freeze dryer retains them at close to the normal size. So dehydration is a more compact storage method, freeze drying is just lighter in weight but does not save space.
A dehydrator is a simple piece of equipment. It has a fan and a heater. The more complex ones have a timer and temperature control. You can get one that will work really well for about $40. Some people spend more - but I have not been able to find a reason to do so, other than wanting one in stainless, or needing white plastic instead of transparent plastic (which off-gasses less and irritates my lungs less), because the cheap ones worked just as well as the expensive ones (I have used many kinds). A decent sized one (with 5-7 trays) will do 5-10 lbs of food, depending on how it is cut and how it is organized. I can do 10 lbs of apples easily in a 6 tray model.
A freeze dryer is a complicated piece of equipment. A small one is about the size of a washing machine (Ok, so they have smaller models now, but not a lot smaller, and they all have an external pump that is pretty good sized that you have to have room for also), but the drying chamber is about the size of your average small dehydrator (it can process 5-15 lbs of food, depending on the size of the unit). It takes a LOT of space for the amount of food you get out of it. It is more complicated to use, and FAR more costly. They are finally down to around $1500 for those small ones (thousands more for bigger ones), they may or may not come down more, because they are simply a complex piece of equipment.
A dehydrator requires no maintenance, and very little in the way of troubleshooting. They are simple to operate, simple to clean up, simple to figure out how to adjust. You generally have an on-off switch. Some have timers, some have heat settings. That is as complicated as it gets.
A freeze dryer is a different thing entirely. It requires maintenance after every load, requires oil and oil changes, has multiple parts and complex settings, gaskets that fail, filters to maintain. Parts break down regularly, or need replacement for maintenance regularly. It operates with a computer panel with multiple settings to adjust, and if things are not set properly, the cycle does weird things. There is a learning curve, and if you don't adjust and work things correctly, it can get messy (as in, oil leaks). Troubleshooting a batch that didn't dry well is a common occurrence, and involves some knowledge of what went wrong, and how to adjust to compensate.
A dehydrator is fairly economical to use. The heating element does not use a lot of electricity, nor does the fan. Foods dry typically overnight, or in 24 hours for high moisture foods.
A freeze dryer can take 72 hours per batch (generally takes more than 1 day), and uses freezing, vacuuming, heating, and fans - it can run through multiple repetitive cycles of freezing and drying for a single batch. It uses more energy to operate, and each cycle is quite a bit longer. Enough that if you are running the thing with back to back loads for weeks (many people do), you are going to see the difference in your electric bill (the Harvest Right company lists operational costs at about $1.20 to almost $3 per day in energy usage - multiply that by the number of days you think you'd use it per year, and remember that many things take more than 1 day). Many people pre-freeze the food, to shorten the cycles, and if you do that, you always need to have room in your freezer for the trays also. The company says that the unit notifies you when the food is done, but reports from users suggest this feature is far from perfect, and troubleshooting is a common occurrence.
A dehydrator has a small fan that produces some noise. It can be in operation anywhere in the house and not be a disruption.
A freeze dryer is fairly noisy. According to Harvest Right (the maker of home freeze dryers), it is as loud as a "noisy dishwasher". You are going to want to have a place to put it where the noise will not bother you.
The argument is made that freeze dried foods store for 15 to 20 years. Some do, some do not. Higher fat foods won't store as long. I've seen (and eaten) freeze dried foods after 20 years. The color has paled, the flavor has gone stale or bitter, and some of them no longer rehydrate well. Very similar to dehydrated foods, but those that I've used after long term storage have actually been in better condition.
Dehydrated foods store just as well, and for just as long, but take WAY less space. Those foods that do not dehydrate well do well with other preservation methods - berries generally can well or are wonderful in jams, preserves, and syrup. I've also eaten home canned foods that were 20 years old (we look for color changes and texture changes, as well as indications of spoilage - where there are no significant indications of the food breaking down, it is safe to eat - storage conditions radically affect storage life), and they were in as good condition as the freeze dried foods, sometimes better. Storing home preserved foods in a cool, dry, and dark environment will dramatically increase storage life, whether you dry, can, or freeze dry, and storage conditions probably have a greater affect on storage life than the method you choose.
Dehydrated foods rehydrate best with hot water, and are fully rehydrated in about 30 minutes. They CAN be rehydrated using cold water, it will take several hours, or overnight, to do it though. They are simple to use if added to meals in progress, and allowed to cook along with the fresh ingredients. Other dehydrated foods are commonly used dry for tasty snacks.
Freeze dried foods are less popular for snacks. The initial feel when you put them on your tongue, or if you chew them right away, is kind of squeaky crunchy. But they go to goo pretty fast, and don't really end up having the intense flavor of dehydrated foods, because the flavor is not concentrated. They rehydrate BEST with hot water, but can be rehydrated with cold water, and generally rehydrate faster than dehydrated foods. Thicker freeze dried foods will not rehydrate well into the center, and those with sauces will often not rehydrate well, because the outside absorbs the water, and then the sauce keeps the water from penetrating well into the center of more dense pieces of food. They have their place in emergency storage where heat is limited.
I can find no justification for the incredible cost and energy usage, and fuss and bother of a home freeze dryer. I have limited physical energy, and extremely limited finances, so I have to be very careful where I use those resources, and want to be sure that whatever I do, I am getting maximum value and results for the expenditure. Other methods of preservation are running rings around freeze drying in terms of economy and simplicity!
I heard someone say, "You can freeze dry ice cream and have ice cream all year even if you have no freezer." Well, that's just silly, of course you cannot! Freeze dried ice cream is not ice cream. It is styrofoam type candy! It is not cold. It cannot be rehydrated back into ice cream! It is just a novelty, not in any way essential or even relevant to what it started out as!
I have noticed that many people who get a freeze dryer are not doing it for practical reasons, but because they are enchanted with the idea of freeze drying everything in the house. I know many canning addicts also, who will can things just because they CAN (pun intended). I've never been that way, I want to know that my effort is necessary or beneficial, and if it is not, I do not do it! Freeze drying is too costly and time consuming for me to do just for a trendy hobby.
If you are thinking about one, I suggest you join a group on FaceBook or elsewhere for using a freeze dryer, and see whether it still sounds like a manageable thing. If so, great. If not, don't apologize, just walk away!
I used to think I wanted a freeze dryer until I heard people talking about actually using one. I no longer have any desire to own one!
The information on this site is presented for informational purposes only, and consists of the opinions and experiences of the site authors. It is not to be construed as medical advice or to be used to diagnose or treat any illness. Seek the assistance of a medical professional in implementing any nutritional changes with the goal of treating any medical condition. The historical and nutritional information presented here can be verified by a simple web search.