The drying of perishable foods and goods is a huge part of human history. Long before the advent of the modern technology, people used salt and other natural resources like Sun and Wind to dehydrate their goods, to increase their useful lifecycle. However, these methods were hectic and not very efficient.
So let’s talk about the differences between some less-crazy and more modern methods: freeze-drying and air-drying foods.
- The processes use different techniques to store food.
- End products look visibly different – even from the original food.
- Moisture content can be 70-98% less than the original.
- Both methods extend shelf life – from days to weeks, months, or years.
- The nutritional value of the end products varies by the drying method used.
- The total cost involved varies by the process.
- Tastes and textures are very different.
- Both methods can rehydrate with varying levels of success and time.
The drying practices have evolved due to the introduction of technology and now you can increase the shelf life of a product by 240 folds, at least. The two most common methods employed for drying are Freeze-dry and Air-dry methods. However, the end result of both these processes is so similar that a layman would find it difficult to tell if a product is freeze-dried or air-dried.
But don’t worry! You will be an expert in differentiating between the two, once you’ve completed reading this blog. So be sure to keep reading.
What are the difference between freeze drying and air drying?
There are a few main differences between freeze drying and air drying. Let’s look at it in a table format. Table 1 summarizes the differences between the two techniques, which will be elaborated in the following sections of this article.
|Process||Freezing and Sublimation||Hot air and Evaporation|
|Retention of Shape||Less Shriveled||More Shriveled|
|Moisture Content||2% – 3%||5% – 7%|
|Shelf Life||Upto 30 Years||Upto 20 year|
|Nutritional Value||90% – 95%||70% – 75%|
|Cost for a Unit||$1,500 – $2500||$50 – $250|
|Taste / Texture||Crunchy and bone dry||Dense with a dry crunch|
|Rehydration Time||8 – 10 minutes||25 – 30 minutes|
If you’d like to see the difference, then make sure you check out my video on YouTube. Don’t worry – you don’t have to go anywhere. Here you go. Although if you want to subscribe to the channel, that would be awesome, too. Then you won’t miss any of the fun videos.
In any case, let’s dive into the big differences now.
Difference #1: The processes use different techniques to store food.
The fundamental difference between the two techniques is the process that is involved in achieving the end product. However, the objective is the same – taking out all the moisture from the products.
In the freeze-dry method, the product is initially frozen to a very cold temperature. After the product is completely frozen, it is shifted to a freeze-drying compartment which is vacuum-sealed. The pressure of this compartment is then reduced so that the ice in the product directly turns into gas, skipping the liquid phase; a process known as Sublimation. This removes all the moisture from the product and it is now ready to be shelved for many years. The image below depicts the journey of a freeze-dried strawberry.
Before discussing the process of the air-dry method, it is important to inform you that the air-dry method is interchangeably known as Dehydration method. However, dehydration has different connotations for different industries, so for simplicity we are using the term air-drying.
In the air-dry method, the product is placed in a chamber and is then exposed to hot air. This hot air evaporates all the water content from the product, making it ready for long shelf life. The image below shows what air-dried (or dehydrated) apples look like.
Air-dried apple slices are one of my favorite treats. They’re not quite chips, but crunchy delicious.
Difference #2: End products look visibly different from each other (and the original).
Freeze-dry method involves a more sophisticated process for drying which causes the overall structure of the product to remain intact. This is why, the appearance of a freeze-dried product is very similar to the original product.
On the other hand, an air-dried product goes through evaporation, and although it also retains its conformation. But due to relatively high moisture content, the shape is more shriveled and wrinkled. This can be observed especially easily in the video I made.
Difference #3: Moisture content can be 70-98% less than the original.
The level of moisture is an important factor to be considered while choosing on a drying method because moisture is the arch enemy of long shelf life and the higher the moisture content in a product, the more quickly it is likely to get spoiled.
As mentioned above, the freeze-dry uses a more effective method which drives out 97% to 98% of moisture (according to the manufacturer). This is because sublimation is done at a very low temperature and pressure which makes it hard for any water molecule to escape its effect.
In my experience, the moisture of freeze-dried food is usually about 95-97% of the original.
The air-dry method uses hot air to evaporate water molecules and it is very likely that some of the molecules are not exposed to sufficient heat for complete evaporation which is why the air-dry method can only remove 93% to 95% of moisture content according to the manufacturer.
In my experience, the moisture content of air-dried food can be anywhere from 70-85% less than the original, depending on how long you air-dry the food (and what it is).
Difference #4: Both methods have different shelf life capabilities
Shelf life indicates how long you can use a product after its making. The shelf life of perishable or fresh foods varies from a few hours to a couple of days. This is because, bacteria and other microorganisms thrive on moisture which is present in these products, so the higher the water content, the more these microorganisms will thrive and the shorter its shelf life would be.
Referring to our discussion above, we can easily conclude that a freeze-dried method has a longer shelf life than an air-dried method. Typically, a freeze-dried product can have a shelf life of up to 25-30 years and an air-dried product can have a shelf life of up to 20 years. That’s according to the manufacturer, anyway.
In my experience, air-dried foods last months to 3-5 years, while freeze-dried foods last 5-25 years (only tested to 5 years).
However, the important thing to note here is that moisture is not the only deciding factor to determine shelf life. The other key variables are the packaging of the product, the temperature at which it is stored after being dried, and the product itself.
Even if you have an effectively dried item, improper packaging and non-ideal storing temperature can drastically reduce the shelf life. Sometimes, all these precautions would still not be enough to overcome the nature of the product and it will decay quickly, but these instances occur very rarely.
Difference #5: The nutritional value of each product varies.
Nutritional value is another important consideration because no one would want to eat a year old food which has no nutritional benefits as well.
Both the discussed methods can sufficiently retain nutritional value. However, since freeze-drying specifically targets only the water molecules, it can retain up to 95% of the nutrients.
In my experience, freeze-dried foods seem to have the same nutritional value as the original food. If there is a difference, it’s not immediately noticeable.
In the case of air-drying, exposing the product to hot air not only evaporates the water molecules but can also heat up some nutrients causing them to break down. As a result, air-drying retains comparatively fewer nutrients, around 75%. That being said, it is still more nutritious than some canned food and products like SPAM.
In my experience, air-dried foods have most of the important nutritional value, but it’s noticeably different than the original food.
Difference #6: The total cost involved varies by the process.
Cost is arguably the most important deciding factor for some people and just in terms of cost, air-drier is the clear winner.
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An air-drier is a basic machine, with a box, some trays, and a hot air regulating mechanism. A smaller air-drier unit can cost up to $50 whereas a larger unit can cost up to $200 to $250. Excalibur is the brand of air-drier I use and recommend. You can check out the same model I have current pricing on Amazon by clicking here.
A freeze-drier, however, is a more bulky and complex machine. It has a main unit and a pumping unit to regulate the pressure. The main unit consists of a chiller which can take the temperature down to -30 degrees Fahrenheit. The main unit also has the freeze-drying chamber which needs to be vacuum sealed before the drying begins. The machine has embedded electronic controls which gives user the option to make custom settings for different products.
Since a freeze-drier machine has additional components, it gives you more control and involves rather intricate processes, it costs way higher than an air-drier. A freeze-drier can cost from $1500 to $10,000 depending on the size and quality of the machine. I use and recommend the Harvest Right brand of freeze dryers. We’ve got the medium-sized model.
Do you want to read more about what it costs to buy and run a freeze dryer long-term? Make sure you read my article on how much freeze dryers actually cost.
Difference #7: Tastes and textures (freeze-dried vs air-dried) are very different.
Both freeze-dry and air-dry retains significant amount of nutrients which in turn implies that their taste is closer to that of the original product. Since freeze-dry retains more nutrients, it tastes better than an air-dried item.
Owing to the increased water content, air-dried products have a dense texture and better color saturation than its counterpart. Air-dried products have slightly sticky appearance and are less likely to crumble.
In contrast, freeze-dried products are less dense and have a crunchier texture. They exhibit less color contrast and are more likely to crumble.
Neither is inherently better, as it really depends on your preferences. For example, I prefer air-dried apple slices to freeze-dried ones. But if it’s peaches? I’ll take freeze-dried, thanks.
Difference #8: Rehydration time and success vary.
Rehydration time is the time required by the dried products to regain the water content which was driven out during the drying process. Rehydration is carried out by simply submerging the product for the required amount of time.
Rehydrating most freeze-dried product typically takes about 10 minutes. This is due to the fact that freeze-drying only affects the water molecules and the rest of the cellular structure remains unscathed – and the fact that freeze-dried foods are usually in small slices or bits. Consequently, when the product is soaked in water, the cells remain prepared to absorb the water again.
In my experience, freeze-dried foods rehydrate well – as long as you are patient. The 10-minute guideline sometimes ends up being more like an hour. Some freeze-dried steaks I’ve tried rehydrating took a full day.
Rehydrating an air-dried product typically takes between 25 to 30 minutes. This is because the cell structure of the product is disturbed during the drying, hence the wrinkled shape. As a result, the cells take more time to absorb when they are in contact with water.
I haven’t had luck rehydrating air-dried or dehydrated foods. They tend to end up mushy, and my family won’t touch them unless they’re incorporated into a soup or stew.
An important thing to note is that rehydration time may vary for different applications. For instance, a freeze-dried soup mix will definitely take more time 10 minutes to rehydrate because it will take more time for each ingredient in the soup to get rehydrated. Similarly, a cup of air-dried apples may only take 10 to 12 minutes to rehydrate.
The trick to know when an item has been completely rehydrated is to observe the color saturation. A completely rehydrated product will have a color contrast similar to the original color.
Having discussed these differences, now the question that arises is this: which is better?
What is better, freeze-drying or air-drying?
The simple answer to the above question is that there is no clear winner here. The best option for one person might not be suitable for another. The things to consider before choosing on an option would include, your budget, how long do you want to preserve the food and what texture and taste you prefer.
If you have a limited budget and are not very particular about your taste palate, then you should definitely go for an air-drier. It is comparatively easy to use, is small in size and will get the job done. Who would want to preserve a product for more than 20 years anyway?
If, however, flavor is a bigger concern for you then the budget then you should consider going for a freeze-drier. The end product you’ll get will be pleasing to the eye and will taste almost as good as the original. The tricky thing with the freeze-drier is its handling. The pressure pump and the freezer chamber controls should be handled carefully to avoid any mishaps. Moreover, the bulky size of the machine will require a lot more space to be placed properly. Good luck finding the required space in your kitchen!
Along with a higher cost prize, freeze-driers have a comparatively higher maintenance costs as well, owing to its added components. So if you can afford all these costs then there is no better option than a freeze-drier. And who knows, maybe you are in possession of a rare herb which you want your great grandchildren to use as well. Now you know how you can accomplish that!
Another important thing to consider is the application of the dried products. If you’re camping or backpacking then you would not want to wait for 30 minutes to be able to eat your food so in these scenarios, freeze-dried food should be preferred.
Lastly, it is essential to point out that irrespective of the pros and cons of these two methods, they are a better choice than canned food items. Commercialized canned foods use synthetic preservative or additives to prolong the shelf life and not a lot of research has been done to study the adverse effects of these preservative on human health. Added to that, freeze-drying or air-drying is usually done in homes so there is a piece of mind that the end product will be safe to use so consider this the next time you go to buy canned food products.
Final thoughts on air-dried VS freeze-dried foods
There really isn’t a better method. There’s just what you can do now – and what you plan for in the future. We started with an air-drying dehydrator first, because that’s what we could buy that fit in our budget. When we could, we added a freeze-dryer to our food storage plan.
Now, we’ve got both. We use air-dried foods for snacks and short-term storage. Then, we use freeze-dried food for longer-term storage – and to keep foods almost perfectly fresh for any time we need them. It makes our pantry practically perfect any time we realize need a forgotten ingredient for dinner.
And if you’re in the market for either product? Here are the ones I recommend you check out.
- Air-dryer (dehydrator) – You can check out the same model I have current pricing on Amazon by clicking here.
- Freeze dryers – I use and recommend the Harvest Right brand of freeze dryers.
It’s important to learn from your own experience, but it’s also smart to learn from others. These are the sources used in this article and in our personal research to be more informed as homesteaders. 🙂