Several people have asked me, “What's the difference between dehydrating and free drying?” or “What's the difference between a dehydrator and a freeze dryer?”. Although they perform similar functions – food is dried for storage – how they do it and the resulting product is quite different. We'll take a look at the equipment involved and the final product.
What's the Difference Between Dehydrating and Freeze Drying?
First, let's take a look at the processes of dehydrating and freeze drying.
Home Food Drying with a Dehydrator
Home food drying uses dry air and sometimes gentle heat. Dehydration can be as simple as laying some flowers or herbs on a mesh screen to air dry, or as complicated as using a specific recipe, time and temperature setting on a commercial dehydrator.
In a commercial dehydrator, the temperature is typically set between 95°F to 155°F, depending on the food being dried. Delicate items like herbs and flowers are dried at lower temps, while meat is dried at higher temps. Fruits and vegetables are dried between 125°F to 135°F.
Home Food Drying with a Freeze Dryer
Home freeze drying super-chills the food down to around 30 degrees below zero, which takes about 9 hours. Then the home freeze dryer kicks on a high powered vacuum pump, which pulls a complete vacuum in the sealed drying chamber. At this point, the food is warmed and water within the food sublimates directly from ice to vapor. The process is repeated (chill, warm) until a moisture sense indicates that the no more water vapor is being drawn off. At this point the unit beeps to notify the user that freeze drying is complete. The user releases the vacuum and double checks the dryness of the thickest food pieces in the chamber. If food pieces are still cold in the center (indicating dampness), additional time is manually added to the cycle.
Dehydrating Versus Freeze Drying – How Does the Food Taste?
As food is dehydrated, it typically shrinks up and develops a leathery feel and appearance. Dehydrated food can be eaten “as is” – think raisins, fruit leather or jerky – or rehydrated. Rehydrating is best done with plenty of water and low slow cooking – think soups and stews, or slow cooked oatmeal with dried fruit.
With freeze dried food, the texture is lighter and more airy. There is very little shrinkage, and many foods have a “melt in your mouth” texture when dry. Freeze dried meat strips that we make for fajitas taste like a meat flavored version of cheese puffs. (We call them “meatos”.) The finished product can be easily crushed or crumbled, so care should be taken if you'd like to preserve whole, large pieces of food. An example of freeze dried food are the berries in commercial cereals that feature real berries. Most freeze dried foods rehydrate quickly, so you can have a hot meal in 5-10 minutes. Think “just add water” heat and eat side dishes or entrees.
Storage of Dehydrated and Freeze Dried Foods
Both dehydrated and freeze dried foods store best in an airtight container with an oxygen absorber for long term storage. That said, dehydrated foods are a little more forgiving if stored less than optimally. Because they take longer to rehydrate, they don't immediately absorb moisture if left out for a short period of time. For instance, I keep jerky and fruit leather that we're eating in plastic zip lock bags or mason jars. They both keep fine for weeks.
Freeze dried foods act more like sponges. Once exposed to air, the clock is ticking. They can go from crisp to soggy in a couple of hours – faster in humid conditions. If you want to store freeze dried food long term, it's essential that it be packed in an airtight container with an oxygen absorber as soon as possible. Initially I started with vacuum sealed mason jars, but I had a number of seals fail in storage. Instead, I've switched to Mylar with an oxygen absorber. So far, so good. The containers I've tested after several months of storage taste freshly packed.
Shelf Life of Dehydrated and Freeze Dried Foods
How long do these foods last in storage? The estimates I've found for dehydrated food storage are all over the place. On the Excalibur website, they give an expected shelf life of 20 years for apples, but only five years for “fruit”. Odd. For veggies they claim 8 to 10 years, and don't offer estimates on meat. Other sites suggest no more than 2-3 months for meats, 1-2 years for other dehydrated foods. In my own experience, after about 3 years, dehydrated fruits and vegetables start to darken and lose flavor. (I keep them cool and out of direct light, vacuum sealed in mason jars.)
The shelf life of properly stored freeze dried foods is nearly universally agreed on as longer. Freeze dried low fat content foods like fruits, vegetables, lean meat, rice, noodles, ect. have a shelf life of 20+ years when packaged properly. Higher fat freeze dried foods and meats have a 10-15 year shelf life. Some commercial freeze dried products are now claiming 30+ year storage life. I'll have to update this post in about 20 years to let you know how my storage turns out.
Dehydrator Versus Freeze Dryer – Comparing Equipment
For home food drying, there are a range of equipment options available – including no equipment at all, as mentioned above. You can build your own unit, use a Sun Oven or other solar dryer, or buy an electric dehydrator. Commercial dehydrator costs range from around $50 at the low end for small units with temperature control, to over $400 for the high capacity stainless steel models. As long as your set up can provide warmth and dry air, it'll probably work. Results may be less than ideal.I have friends in warm humid areas that could not dry larger food pieces without molding in a budget model with no temp control. (I do not recommend electric dehydrators without a temperature control for this reason. If you're going to get a dehydrator, get one that does the job right.)
You can learn more about dehydrator types in the post Getting Started with Home Food Drying.
For home freeze drying, at the time of this post, there's only one company making home units. (This is to the best of my knowledge. If you know of another manufacturer, let me know.). That company is Harvest Right out of Salt Lake City, Utah.
As mentioned above, the process of freeze drying is significantly more complicated than dehydrating. The drying chamber must form a perfect vacuum. Materials inside the unit must be able to withstand extreme cold and moderate heat, and to swing between the two. The sensors need to be able to determine when to cycle the machine. There are significantly more moving parts and higher performance demands. As such, the price point is significantly higher. The smallest units start at around $2600, the largest units in a stainless steel finish are over $4000.
Dehydrating or Freeze Drying – Which is Better?
A freeze dryer is a big investment, but it's the only way to create truly long term shelf stable storage foods at home. If you plan to rotate stock more frequently and don't want to preserve meat and dairy, then a dehydrator can probably get the job done.
I still use a variety of food storage techniques, and I don't plan to change that. Canning, fermenting, drying, freeze drying, freezing, root cellaring – each method brings something different to the table. The flavors and textures are different, how we use the food is different. I like having options.
I think of our freeze dryer as a type of food insurance. While we have been enjoying freeze dried snacks and quick meals, I'm also tucking food away for long term storage. Food prices keep creeping up, and the last time my husband lost his job, it took around a year to find a new position. I feel better knowing that we have some of the basics covered.
What food preservation techniques do you use, and what do you like about them? What techniques would you like to learn more about? Leave a comment below and let me know.
I’ll continue posting what we’re drying on Instagram, and sharing additional posts to address questions show off the yumminess. If you choose to purchase a Harvest Right freeze dryer through my site, I receive an affiliate payment at no extra cost to you. (Thank you.)
You may also find useful:
- Home Freeze Drying – The Good, The Bad and The Ugly – my review of the Harvest Right Freeze Dryer
- 11 Freeze Drying Mistakes to Avoid for Best Food Storage Quality
- New to Food Preserving – Start Here