Estimated reading time: 8 minutes
Many of us experienced the shock of seeing empty produce bins and store shelves in our local supermarkets this year. The scarcity of certain foods during the pandemic may have led you to explore new ways to preserve and store food.
If you seek long-term storage and foods that are light to pack and carry, you can’t beat freeze-drying. In this article, we’ll examine what freeze-drying is, its benefits and drawbacks, and some of the basics you need to know about using this food preservation method at home.
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What Is Freeze-Drying?
Also known by its scientific names, lyophilization or cryodesiccation, freeze-drying is a dehydration process that involves freezing the food and then lowering pressure before removing the ice by sublimation. Sublimation is the transition of a substance from the solid to the gas state without passing through the liquid state.
Freeze drying can remove 98 percent of the water in food while dehydration removes about 80 percent. Since it is water that can cause food to spoil and deteriorate, freeze-dried foods can have a remarkable shelf life of 25 years or more.
NASA began sending astronauts into space with freeze-dried foods back in the 1960s but, contrary to what you might think, the process did not originate in a modern lab. For centuries, the people who live in the Andes Mountains of South America have been freeze-drying potatoes — called chuño — and other foods naturally.
During World War II, medical personnel used the process to transport blood to field hospitals. And today, you can find buckets and packs of a variety of freeze-dried foods for sale in supermarkets.
What Are The Pros And Cons Of Freeze-Drying?
The main advantage of freeze-drying is that extended shelf life of up to 25 years or more when stored correctly in a cool, dry place.
Here are other benefits of this form of food preservation:
- Compact. The water in food takes up space. When you remove the water, the item takes up a lot less space to carry and store.
- Lightweight. Water content also adds weight. Freeze-dried foods are light to carry, which makes them perfect for backpacks and bugout bags.
- Easy to prepare. Some freeze-dried foods taste great as is (strawberries and peas, for example). Others just need a little water for rehydration.
- Nutritious. Because it requires no heat, the freeze-drying process retains most of the food’s vitamin content.
- Flavorful. Most or all of a food’s flavor stays intact throughout the process.
As great as freeze-dried food is, there are also several disadvantages:
- The cost. The Harvest Right company sells freeze dryers for home use that range in price from $2195 for a small machine to $3395 for a large machine. You also need to add in the cost of trays, mylar bags or other storage containers, and oxygen absorbers.
- Time. It takes a lot of time to freeze-dry foods. Depending on the size and model of home freeze dryer you have and the amount of food you are preserving, it takes 20 to 40 hours per batch to complete the process. This timeframe does not include packaging time.
- Texture. Although a freeze-dried food may taste similar to its fresh state, it may have a noticeable different texture. In some foods, this difference doesn’t matter; in others, it does.
- Limitations. You can’t freeze dry everything. Foods that are high in fat or oil or contain a lot of sugar do not handle the process well. Foods to avoid include peanut butter, chocolate, jams and jellies, syrup, butter, and honey. Bread and other bakery items do not freeze-dry well either. Also, avoid freeze-drying leafy greens, such as spinach and kale, which become wilted and soggy. As you might expect, watery fruits, such as watermelon, do not handle the process well.
Can You Freeze Dry Foods At Home?
The answer is yes, but the process is complex. Here are the basic steps:
- Freeze the food.
- Dry the food through sublimation.
- Further, dry the food through desorption (the opposite of absorption).
In a standard freezer, it can take several months to freeze-dry food properly. A big concern with that long time frame (other than the length of time itself) is possible bacterial growth. Freeze drying does not kill bacteria, but because a freeze dryer removes the water more quickly, there is much less chance for germs to grow. Your results will be best with the use of a freeze dryer rather than using your own freezer.
If you are handy, another option is to build your own freeze dryer. This video explains the DYI process. It’s a detailed and helpful video but be forewarned that the narrator talks fast. If you are like me, you’ll frequently need to hit the pause button to fully grasp what he is explaining.
Whether you purchase or build your own freeze dryer, here is the process for using the machine:
- Place food on trays in the freeze dryer chamber.
- The dryer then flash freezes the food with temperatures of -30°F or colder.
- A pump removes chamber air, creating a vacuum.
- Because of the low pressure that now exists in the chamber, the ice changes to vapor.
- A condenser pulls the vapor from the chamber.
Freeze drying food involves a bit of a learning curve, and you will undoubtedly make some mistakes along the way. Some foods take longer than others to process, for example. Here are some tips to help keep those errors to a minimum.
- Peel or cut large fruits and vegetables before freeze-drying. Place the skin side down on the tray.
- Blanch potatoes before freeze drying to prevent them from turning black during oxidation.
- Cook or blanch raw veggies before freeze drying to prevent toughness.
- Small pieces of food tend to do better than large pieces. They also take less time to rehydrate.
- Line trays with parchment paper or silicone mats to save on clean-up time.
- If you freeze-dry uncooked meats, eggs, or poultry, be sure to label them as raw before storing. If you cooked the food before freeze-drying, you could eat it right away. If you freeze-dried it raw, prepare it as you would prepare fresh raw meat. You can rehydrate both raw and cooked meat in heated broth.
- Buy your favorite foods in bulk quantities when they are on sale. The more you freeze dry foods, the more you make up for the expense of buying a machine.
- Store your foods in sealed mylar bags with oxygen absorbers in a place that is away from moisture and light.
How To Rehydrate Freeze-Dried Foods
You can eat many fruits and vegetables in their freeze-dried state without rehydrating them. Rehydrated fruit works great in smoothies or on top of yogurt, cereal, or oatmeal. You can add freeze-dried veggies right into soups and stews, and let them rehydrate that way.
If you want to return them to their natural state or want to cook them, you can rehydrate items by letting them soak in a bowl of water. Some foods rehydrate well if you spritz them or spoon water over them. This video clip shows how to freeze dry and rehydrate avocado slices – although they taste great freeze-dried. And this video shows how to rehydrate the components of an entire meal quickly and easily.
The Harvest Right website includes lots of information on how to freeze-dry and rehydrate freeze-dried foods. For instance, this article discusses foods you might not have thought you could freeze dry.
You’ve probably been thinking about freeze-drying as a way to preserve and store food for the human members of your family. However, freeze-drying foods for your pets is another idea. Even if you don’t want to serve your pet homemade freeze-dried food on a regular basis, it is handy if you take your dog on a hike or vacation.
Also, since freeze-dried pet food takes up much less room than regular pet food cans or bags, you can add some freeze-dried food for your furry friends to the shelves of your survival pantry.
Hint: Most dogs don’t mind eating freeze-dried food as is – just make sure it is fully cooked first.
The COVID-19 pandemic continues to teach us many lessons. Forced to work from home and shelter in place, more people are cooking at home than they were before. And many of us are more aware of what we have and don’t have on our pantry shelves for emergency use.
With its exceptionally long shelf life and nutritional benefits, freeze-drying food for long-term storage may just be a good project for you to tackle next. Here are a few more resources to check out:
- Yes, You Can! And Freeze and Dry It, Too by Daniel Gasteiger
- Preserving Everything by Leda Meredith
- The Complete Guide to Food Preservation by Angela Williams Duea
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