Learning how to freeze dry food1 is as much a skill as it is a trend. Various cultures across continents have had their traditional methods and processes linked to community practices that can be said to act as precursors to the modern freeze-drying processes.
The basic idea is rooted in the concept of preservation. With the emergence of settled communities over the process of evolution, the preservation of food emerged as the cornerstone of a sedentary lifestyle.
In the present era, preserving food at home is a great way to ensure food security in case of an emergency and to have healthy, organic homemade food all year long.
Numerous methods can be used to preserve food at home including freezing, canning (water-bathed as well as pressure canning), cold cellaring, infusing, and fermenting.
1. What is Freeze Drying
Freeze drying is a popular method to make use of low temperatures to dry food and preserve it for the long term. It is generally used to preserve perishable materials. Once freeze-dried, the materials have the added advantage of becoming much more convenient in terms of their transportation.
The purpose of freeze-drying food is to produce clean, whole, and nutritious food ingredients with a highly prolonged shelf life. This makes food products versatile, accessible, and convenient for consumers
2. How to Freeze Dry Food: The Process
The process involved in freeze drying comprises three distinct sub-processes: freezing, primary drying (sublimation), and secondary drying (desorption). This involves freezing the food material to reduce the pressure and then introducing heat to allow the water that has frozen in the food material to directly become vapor.
When freeze-drying is done properly, it can significantly help in decreasing the drying duration by up to 30%. Freeze-drying makes food resistant to getting spoiled and can last up to 25-30 years. It doesn’t require food to be rotated and reduces the need even worry too much about it getting spoiled.
Freeze-drying is effective when dealing with fruits and vegetables. It is also known to have worked quite perfectly to preserve meat, fish, dairy, eggs, ice cream, and even fully-cooked meals. Further candy that has been freeze-dried also has a big consumer market. Let’s delve deeper into three distinct sub-processes.
2.1. Freezing
The very first stage of freeze-drying is quite obviously the process of freezing. Foods are first frozen to well below 0°F.
2.2. Sublimation
The following stage after freezing is drying by sublimation. At this point, the food is exposed to a vacuum to make the water sublimate – it turns straight from ice into vapor.
2.3. Desorption
Finally, in the last step, one has to engage in desorption drying. Here the air and water vapor are divorced. This is done by again enhancing the temperature and pressure.
3. Types of Foods that are Perfect for Freeze Drying
Freeze drying is known to have worked wonders with foodstuffs that have a lot of water content in them. So, food items like fruits, herbs, fish, vegetables, dairy-based products, coffee, and meat are all amenable to freeze-drying food.
Foods that work well with freeze-drying include fruits (like kiwi, apricots, and oranges), vegetables (especially those with high water content), sliced meat chunks, fish (sliced into small chunks), dairy products (such as cheese), coffee and other fruit-based liquid beverages like juices, prepared meals such as lasagna or even soups.
3.1. Freeze-dried Meat
Freeze-dried meat2 has a miraculously longer shelf life than frozen meat and can last 25-30 years at room temperature. So, make sure to set some sliced freeze-dried meat aside in case you are a believer in the apocalypse theories. You can never be too careful, am I right?
To rehydrate freeze-dried meat, you simply have to use boiling water over it, until the food expands. After this, you may remove all excess water and enjoy your meal like it was fresh off the stove!
Of course, sourcing freeze-dried meat can be difficult these days due to high demand, a shift towards veganism, and the issue of lapses in the supply chain due to international events and forces.
3.2. Freeze-dried Fruit
Freeze-dried fruit is possibly the most common type of freeze-dried food out there. All those chocolate-covered berries out on the supermarket shelves that are just secret guilty pleasures we like to forget about, yes, those are the ones you never even realized had an element of this.
Freeze-dried fruit has undergone a process that removes almost all of its moisture, leaving it light and crunchy. Freeze-dried fruits are available in different varieties such as diced pineapple, diced apricots, diced apples, and sliced strawberries among others.
Most beginners just starting out to understand the nitty-gritty details of how to freeze dry food are advised to start with fruits that are in season and easily available around their local markets.
3.3. Completely Freeze-dried Food
Completely freeze-dried food is a variation of freeze-dried fruit, with the only difference being that it has more severe moisture loss as the very basis of its production of the end product.
Therefore, it has a dehydration process that removes almost all water/moisture/liquid content from the food material. This reduction of liquid water content via dehydration preserves the food for an even long-term duration. This is ideal for long-term storage.
The process is a slightly modified form of the normal freeze-drying process. It consists of four stages. the first stage is pretreatment. This is followed by freezing. After freezing the primary drying takes place. The final stage is secondary drying.
3.4. Dehydrated Food
Dehydrated food is rendered as such by making effective use of a dehydrator. Dehydrated foods come in handy in case you decide to go and have a camping weekend, or if you are backpacking through the country, and more importantly during emergency circumstances.
Since dehydrated food is lightweight it is easy to carry and transport and has a long shelf life which means it can survive the ravages of time that other food items can’t when they are in the non-freeze-dried state.
Dehydrated fruit is nutritious and often has the capacity to make for a delicious snack that can be enjoyed not only in the comfort and confines of home but also on the go.
As per industry recommended temperature standards, for dehydrating fruit 135°F (57°C) is ideal with the exception of limes and lemons, which turn brown unless dried at a lower temperature. Dehydrated fruit has several benefits, but burnt dehydrated fruit does not make the cut.
4. Different Ways to Freeze Dry Food
4.1. Commercially Freeze-dried Food
Commercial freeze-dried food first became a viable option for industry-scale production due to the need to provide food at times of war.
Modern warfare, trench warfare which required soldiers to fight in foreign lands, carry everything on them into the battlefield, and stay for long durations in regions where proper preservation techniques couldn’t be maintained and observed ultimately gave way to food than can be made anywhere and everywhere.
Interestingly, coffee was also one of the first freeze-dried food products to be manufactured commercially, but now the pool has widened to include vegetables, meats, fish, fruits, dairy-based products, herbs, and even food flavorings. Now several behemoth companies have made their fortunes from the commercial production of freeze-dried food.
The instant food market is expanding fast due to that reason. Further globalization and increase in connectivity all over the world, as well as changing patterns of settlement and work-life, have led to an increase in the market and consumption of commercially produced freeze-dried food.
4.2. Freeze Drying Machine
Freeze drying is a process that involves two simple steps: freezing and vacuum drying. Foods are first frozen to well below 0°F, and then the frozen water is removed by placing the food in a vacuum chamber under low heat.
For the working of this process, we can rely on vacuum pumps. These pumps serve are devices that help us create a low-pressure vacuum, allowing us to push air molecules out of the sealed bag.
Hence, the vacuum pump’s main function is to change the pressure in a contained space. The vacuum generation process starts by expanding a sealed chamber and generating a vacuum. One of the most widespread applications of vacuum technology is in the food processing industry.
4.3. Harvest Right Freeze
The Harvest Right freeze dryer can freeze-dry anything from dairy foods to meats and poultry to eggs and fruits. It is based on the principle of maintaining the original nutrition of foods.
This is unlike dehydration which can destroy up to 50% of nutrients in some foods. Harvest Freeze drying is one of the best methods of food preservation because it retains the original flavor, color, and nearly all of its nutrients.
4.4. Home Freeze Dryer
A home freeze dryer is a rather convenient device to have if you are serious about freezing dry food. It empowers you to preserve food by freeze-drying it. As simple as that.
Home freeze-dried food can retain its original flavor, in most situations its color, and nearly all of its nutrients. Home Freeze drying using a home freeze dryer can be broken down into two basic simple processes: freezing and vacuum drying.
Once frozen, the food is placed in a vacuum chamber where the temperature is raised and the pressure lowered. This causes the ice crystals in the food to sublimate directly from solid ice to water vapor without passing through a liquid phase.
5. How to Store Freeze-dried Food?
5.1. Sealed Bags
Freezer bags are plastic bags designed to store food in the freezer, protecting it from freezer burn and keeping it fresh for longer periods. Freezer bags are available at many retailers and online grocery shopping websites and platforms.
Freezer-safe plastic bags are designed to be thicker than regular plastic bags, which helps to prevent tears and punctures. They make sure that the food is isolated and that no air is able to pass inside. Freezer-safe bags are ideal for long-term food storage, such as anything longer than a month.
Cellophane/plastic bags with the ability to isolate material can be useful to store dried food in order to freeze it for future use. Plastic is non-responsive and helps to curtail the germination and reproduction of bacteria.
5.2. Sealed Vessels
A sealed container is a container vessel that allows us to close it tightly to prevent anything from going inside, including air, moisture, or other substances. Sealed containers are used for a variety of diverse purposes.
These purposes include not just your typical food storage but also others as well such as garbage disposal and transportation of goods. For this reason, there are different types of sealed containers available in the market.
5.3. Airtight Containers
Air-tight containers are similar to sealed containers. They are a type of sealed container, with a slight difference in the type of seal that is used to ensure that the food is isolated from all elements including water, air, and moisture.
These are also used to store food and other items to keep them fresh for longer periods of time. Air-tight containers have a seal that prevents air from entering the container, which helps to preserve the freshness of the contents.
6. What are the Benefits of Freeze Drying
Freeze-drying 3is a highly beneficial process. Firstly, it allows for storing food across longer durations, especially food items that would otherwise be considered perishable and therefore necessary to rotate or consume within a short duration of time.
Since freeze-drying comprises a high-quality dehydration method that operates at low temperatures, it also helps to preserve the nutritional value of the food, authentic original taste, and appearance. Even heat-sensitive compounds of food products are controlled.
This means that freeze-dried foods are a healthy food choice because they retain nutrients and phytochemicals in foods. They are the obvious choice if you are headed camping or can’t cook food due to a shortage of fuel or electricity, or in case there is any emergency situation.
7. What Factors Can Affect the Shelf Life of Freeze-dried Food?
Like for other substances, we also need to be careful about the shelf-life of food items. The shelf life of freeze-dried food can be affected by several factors. Moisture is one of the most significant factors that render items severely perishable.
Air-tight containers, sealed bags, cellophane, and other isolation vessels and agents can help restrict the reduction of the shelf life of freeze-dried food. Most importantly, it is necessary to reduce the exposure of food items to moisture during the process of freeze-drying.
To learn how to freeze dry food is to keep all of these things in mind and ensure the best quality of your freeze-dried food.
7.1. How to Get Longer Shelf Life for Freeze-dried Food?
There are several ways to extend the shelf life of food. One way is to store food in a cool, dry place with low or no moisture in the air. There are many foods with a long shelf life that can be stored for emergencies or unexpected job loss as was the case during the pandemic.
Canned fruits and vegetables have a long shelf life and can generally last up to two to five years if stored properly.
To extend the shelf life of fresh produce, packaging improvements such as modified atmosphere packaging (MAP) can be used. MAP is important as it adheres to controlling the gases that surround an item, limiting the oxygen that surrounds fruit will help prolong its shelf life.
8. Other Food Preservation Methods
There are several methods of food preservation outside of freeze-drying and the more traditional chilling and freezing. These include sun-drying/air-drying canning, dehydrating, fermenting, and salting.
8.1. Air Drying
Air drying is the method of getting rid of moisture from surfaces by using air. It has a fairly simple technique to it that involves letting the air dry the moisture out of food items.
While air-drying one needs to keep a close eye on the food material because, after a certain point, they need to be stored properly and removed from air-drying any further. Further, sun-drying is a form of air-drying that involves putting items under sunlight and letting the natural heat work its magic.
This process is the renewable method of dehydrating food items and is therefore beneficial even to the goal of ensuring that the environment isn’t harmed as we go about our dietary patterns and activities.
8.2. Canning
This is a method of preservation that is related to the developments of modern industrial practices and developments. It has been in the fold since the Industrial Revolution.
It involves heating food in jars to kill bacteria and sealing them to prevent contamination. It can in some ways be seen as an ancestor to freeze-drying food, in terms of the storage component.
8.3. Fermenting and Salting
These are the ancient techniques of food preservation that have remained popular due to their unique flavor as well as their cultural significance in many parts of the world. Fermentation itself is a process that is based on the principles of microbial action and intentionally spoiling the food.
But it works only when the microorganisms are kept in check. Fermented foods include pickles of various kinds, region-specific condiments, staples like kimchi in South Korea, miso paste that’s used widely in various countries, different types of tea, and most prominently the entire wine industry.
Fermented food4 also has several health benefits and therefore kills two birds with one stone. It preserves food with flavor and helps digestion (as well as other bodily processes).
Salting on the other hand aided the preservation of meat and fish in earlier times before refrigeration practices improved. Therefore, fermenting and salting are such preservation techniques that are second to none when we have to choose alternatives around how to freeze dry food.
These have, in many cases cultural significance and are associated with community memory. Mastering the freeze-drying of food items, therefore, needs to be situated in this context which features a rich history of preservation methods and techniques that have come down to us across generations.
As you get down to taking freeze-drying your food seriously, you participate in this process of evolutionary progress.
For more information on how to dry freeze your food read 3 Amazing Ways to Freeze Dry Food.
- Harper, J. C., and A. L. Tappel. “Freeze-drying of food products.” Advances in Food Research 7 (1957): 171-234. ↩︎
- Chipault, Jacques R., and John M. Hawkins. “Lipid autoxidation in freeze-dried meats.” Journal of Agricultural and Food Chemistry 19.3 (1971): 495-499. ↩︎
- Duan, Xu, et al. “Technical aspects in freeze-drying of foods.” Drying Technology 34.11 (2016): 1271-1285. ↩︎
- Parvez, Suhel, et al. “Probiotics and their fermented food products are beneficial for health.” Journal of applied microbiology 100.6 (2006): 1171-1185. ↩︎
Last Updated on by Sathi
