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How Does Freeze-Drying Work?

How Does Freeze-Drying Work?

Apr 06, 2022

Janette dArgy

How Does Freeze Drying Work 

From doomsday preppers to frugal enthusiasts, many people have become intensely interested in freeze drying over the last few years. Freeze-dried foods are famous for their use in emergency kits, lunch snacks and even freeze-dried candies. But have you ever considered how it works?

The term “freeze-dry” is both intuitive and cryptic. It would be easy to piece out that anything preserved through this method becomes dried through freezing. Not included as part of the ever-so descriptive name is how the drying works. Drying is an essential part of the process, but how does it happen?

The three phases of freeze drying

When preserving food this way, there are three primary phases. 

  1. Freezing
  2. Primary Drying
  3. Secondary Drying

Freeze-dryer machines move foods through these three phases to complete the preservation process. Food needs to go through each stage to turn out correctly. Missing any of these phases is enough to hinder the freeze drying process.

Even though freeze drying consists of only two states, there are two parts to the drying process, hence the need to separate the drying process into two separate phases.

Freeze Drying is like a three act play. First act is where the food is frozen; in the second act the food is basically sent to outer space (no air pressure, no heat); act three finishes drying and gets it ready for packaging. 

Act One: Freezing

In this step, the trays of food are loaded into the machine and frozen. I mean frozen the regular way, not "born of cold and winter air and mountain rain combining". It freezes down to -50 degrees. That's 50 degrees below ZERO or 82 degrees below "freezing.” Once the food is THAT COLD, all of the water, liquid, fluid, moisture, H2O, whatever...has become ice crystals. 

It is important for the process to work properly so the ice crystals aren’t too big and not too small so that they can evaporate without affecting the texture of the food. 

Act Two: Primary (Sublimation) Drying

The machine uses a vacuum pump to pull almost all of the atmosphere out of the chamber. So, now it's like we've sent the food into outer space. No warmth, no atmospheric pressure. Conditions are right for what scientists call "sublimation" drying (which is a word used here to describe when H2O skips the liquid phase and goes straight from solid ice to steam vapor). 

The machine ever so slowly warms just the trays to around -10 degrees F. This is the tricky part. Because there is no (or very little) atmospheric pressure the temperature needed to turn the ice crystals into vapor (sublimate) is also very low, only about -20 up to +0) As the temperature comes up a little the ice crystals become vapor and condense onto the still frozen chamber walls. 

Act Three: Secondary (Desorption) Drying

In the final act of the play, desorption drying begins. At this point the food is only mostly dry - about 95%. There is a big difference between mostly dry and all dry. The machine now warms the trays further, while still maintaining the vacuum inside the chamber. It slowly warms the shelves up to over 120 degrees F.  

Now, because the bulk of the ice crystals are gone, the texture of the food remains the same no matter the temperature (up to 150deg!). Once the sensors read no more vapor in the chamber, the play is over. The food is warm and dry and the chamber walls are covered in condensation ice. 

Why use freeze drying to preserve food?

Removing the water from any organic material increases its shelf life. In the case of food, you can store it at room temperature on a shelf for up to 25 years without it spoiling! This longevity means you can save the leftovers from tonight’s meal for your grandchildren! It sure puts freezers and refrigerators to shame!

Most people will be using freeze-dried foods in emergency kits, camping meals, or even simply as snacks for lunch or road trips. The applications are limitless!

You can eat freeze-dried food plain or rehydrate close to its original state. It may be used for freeze-dry berries and vegetables, but you can do much more. Given the proper preparation, you can preserve entire meals for decades!

What does freeze drying do to food?

When preserving food through freezing and vacuum drying, it often retains 97% of it’s original look, flavor and nutritional value. Not all food looks similar after being treated, though. Some foods will expand and become fluffy (this is common with candy processing), and others will hold it’s original shape.

In every case, since all food has had its moisture removed, the texture will usually change in the frozen state. Without water, bread can’t be moist, jello can’t jiggle, and soup can’t slosh. 

What does freeze-dried candy taste like?

A few years ago, a trend started for freeze drying candy. It became an internet sensation! 

Freeze drying removes most of the original texture from candies, making them fluffy and crunchy. The results? You don’t have to worry as much about struggling to get the rest of that saltwater taffy unstuck from between your teeth!

Many candies will enlarge in size, become light and crunchy, and have enhanced flavor. It’s a great way to enjoy your favorite sweets in a new way.

Rediscover your favorite candies with Candy Jan!

Have you ever wondered what your favorite candy would taste like freeze-dried? There’s an easy way to find out without going through the trouble of buying a freeze-dryer yourself!

At Candy Jans, we love preparing candy for you to enjoy! We sell a wide assortment of your favorite candies ready for all your taste-experiment needs. Visit our website to order now or contact us for special requests.

We are excited for you to rediscover just how much you love your favorite candy by experimenting with freeze-dried candy!