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What Is Freeze-Dried Food?

what is freeze dried food definition

Many people contact us with questions around what makes food freeze-dried and how our meals are made! We've covered many of the common questions on our FAQ, and today we're going to dive a little deeper on some of them.

Let's do a little myth-busting and Q&A today around this topic! If you still have any questions after reading this blog, let us know by sending us your thoughts through our Contact Us form. 

what is freeze-dried food

So what exactly is freeze-drying and freeze-dried food?

Did you ever eat Astronaut ice cream growing up? That's freeze-dried ice cream!

Freeze-drying, or lyophilization, in it's most simplest definition is a process that removes moisture by freezing a product and then utilizing a vacuum to sublime the moisture leaving a almost 100% dry product.

Now let's dive in a little deeper!

This moisture removing process is most commonly used in pharmaceuticals, biochemistry and food. This relatively new technology allows solids which contain moisture or liquids that contain some solid matter to be dried almost to the point that zero moisture remains. An example of a solid which contains moisture would be like an apple (or any other solid food), while an example of a moisture that contains some solid matter would be like a tomato sauce! 

The freeze-drying process involves a few steps in a very specific order:

  1. Raw or cooked food is placed on trays within a freeze-dryer.
  2. The machine freezes the food to a temperature between -30F and -50F . The food must be fully frozen at an extremely low temperature.
  3. After the food has been frozen, the machine pulls a vacuum while slowly increasing the temperature within the machine. 
  4. This combination allows a chemical process called sublimation to occur. (You probably haven't thought of sublimation since high school chemistry!)
  5. As the moisture sublimes from the food, the machine initiates a drying cycle until a certain vacuum pressure and food dryness is reached.
  6. After the initial drying, a second and final drying period occurs to ensure that the food is thoroughly dried.

So while that's the technical explanation, I'm sure those 6 steps still leave you wondering, 'Okay, but what does that really mean??'

Let's take another look at sublimation and why this is important.

Sublimation is the process where solids turn directly into gas without ever going through a liquid phase. A common example of this is dry ice making a spooky fog during Halloween. For our food, this means that the ice changes into vapor without ever becoming water! It's actually a pretty cool process! And this process is why the freezing step is so important because any water that is not frozen solid at a very low temperature will not turn directly into vapor and will instead turn into a liquid. This causes a very different drying process (dehydration) to occur. We've experimented for months and run countless cycles to determine how long food must be frozen for this sublimation process to occur!

what is sublimation definition 

The sublimation process is what makes freeze-dried food have its distinguished appearance and texture! Freeze-dried food looks near identical to non freeze-dried food. Many people are often shocked that when they open a Bushka's Kitchen pouch they are able to visually distinguish the different food ingredients! Apples look like apples, and brussel sprouts look like brussel sprouts!

Because of how the moisture is removed from the food, the texture of freeze-dried food is very airy and crunchy. This is key to why freeze-dried food rehydrates so well! The freeze-dried food is so porous and looking to absorb moisture that when you add hot water, the food almost instantly absorbs it and returns to a near identical appearance. This is a big differentiator between dehydrated food and freeze-dried food. Dehydrated food usually takes between 15 to 20 minutes to fully absorb the water you add; freeze-dried food is almost instant, though we recommend letting sit for around 3 minutes so that the food can absorb as much water as possible before you consume. 

How does freeze-dried food differ from dehydrated food?

Naturally, this leads to our next question which is how does freeze-dried food differ from dehydrated food? We've written a full blog on this which you can read here.

Dehydration in its most basic form is heat and airflow. Food is placed on trays where warm air is circulated throughout the dehydrator to slowly dry out the food; this process removes most of the moisture in food but not as much as freeze-drying. This is why freeze-dried food has a longer shelf life than dehydrated food.

One of the most noticeable differences between dehydrated food and freeze-dried food is the appearance of the food! Dehydration causes the food to get really small and hard; it's basically food that has shriveled up as the moisture was removed. 

In this image, you see jars of freeze-dried squash vs a jar of dehydrated squash. The dehydrated squash takes up less volume, but less closely resembles raw squash!

freeze-dried squash vs dehydrated squash

Is freeze-dried food the same as frozen food?

Nope! They are completely different. While freeze-dried food does involve a freezing step, the end result is not a frozen product. Frozen food must be kept, well, frozen and has a shorter best by life. Freeze-dried food is completely shelf stable and can have a shelf life of multiple years!

Is freeze-dried food healthy?

Depends on the food! Ice cream is after all ice cream!  Freeze-dried food is really no different than regular food! It simply doesn't have moisture. 

While there is limited research specifically on freeze-drying technology, the research that has been completed shows that freeze-dried food retains an almost identical flavor, color, texture and nutritional profile to non freeze-dried food with some nutritional loss for water soluble vitamins (1) (2). When comparing freeze-dried to other preserved food, freeze-dried food most closely matches fresh food.

With the exception of certain vitamins, the nutrition profile is virtually unchanged. This means that calories, sodium, sugars, etc are the same as it's fresh counterpart! So don't binge eat a bag of freeze-dried strawberries! Even if it doesn't feel like you are eating a lot, you are still consuming the same amount of calories as if those were fresh strawberries!

Do you use chemicals to preserve your freeze-dried food?

Nope! We use no chemical preservatives or additives in our meals.

There are two culprits behind food spoiling: moisture and oxygen.

Our freeze-drying technology removes the moisture from the food. To remove the oxygen, all food is vacuum sealed within the pouch with an oxygen absorber added into the pouch as a secondary safety measure. We also use very specific material in our pouches so that they act as an excellent barrier against moisture and oxygen.

 

Whew! That was a long one! I hope that clarified any questions you may have around our meals; if not, let us know through our Contact Us page!

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Bushka's Kitchen provides ready-to-eat, lightweight food for every type of busy lifestyle, whether that's backpacking, traveling, parenting, or an active life. Browse our nutritious, gourmet food and stock up for your busy life!





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