Dehydration is a type of freeze-drying, commonly referred to as lyophilization. To remove the water content of food, it is first frozen. The best drying technique is generally agreed to be freeze-drying. As a result, the food and pharmaceutical industries frequently use it.
In fact, you can easily purchase a large variety of freeze-dried foods in your neighborhood supermarket, from ready-to-eat meals to fruits or snacks.
This page goes into further detail on freeze-drying, including what it is if it is beneficial, and how to do it at home.
What is Freeze Drying?
A dehydration method based on the sublimation of water in a product is freeze-drying or lyophilization.
This indicates that the water content of the product switches directly from a solid to a gaseous state, or from ice to vapor.
For a few reasons, freeze-drying is regarded as a high-quality dehydration technique, including:
It operates at low temperatures, helping to maintain the nutritional value, flavor, and warmth of a product and heat-sensitive substances
Because freezing stops chemical and microbial activities, it dramatically slows down how quickly a product deteriorates (thereby extending its shelf life).
How does Freeze Drying Work?
About 80%–95% of raw foods are made up of water, which can be further separated into “free” and “bound” water. Bound water does not freeze, whereas free water does.
All free water must be extracted throughout the freeze-drying process, along with some bound water, and free water must always be kept frozen. In actuality, this is the most difficult stage and the main distinction between freeze- and vacuum-drying.
Three processes make up the freeze-drying procedure.
Freezing: Under atmospheric pressure, the product is frequently frozen.
Primary drying, sometimes referred to as good freeze-drying, is the phase of sublimation where frozen-free water is eliminated.
By eliminating the remaining bound water, secondary drying often referred to as desorption drying, dries items to the required humidity level.
Given that the presence of liquid water may alter the product’s composition, shape, and physical qualities, freeze-drying should be done under controlled circumstances that do not melt the water.
That would probably result in a substantial decrease in the product’s shelf life.
The substance develops a highly porous structure after frozen water is sublimated out of it. However, adding water almost instantly rehydrates the product.
Is Freeze Dried Food Nutritious?
Foods that have been freeze-dried are a healthy choice. Due to its many advantages, freeze-drying is actually one of the most popular dehydration techniques.
One of the finest methods for retaining the activity of healthy plant substances, like phytochemicals and minerals, while keeping color, flavor, and structure is freeze-drying. Because of this, it is frequently utilized to create high-quality food products.
According to studies, freeze-drying, as opposed to other drying techniques, is the best in preserving antioxidants like anthocyanins, flavonoids, ascorbic acid, or vitamin C.
Antioxidants are helpful substances that support your body’s defenses against the negative consequences of oxidative stress. They also contribute to the health advantages of the majority of fruits and vegetables.
However, depending on the fruit, the converse may also be true, even if freeze-drying occasionally even results in an increase in a fruit’s phytochemical content.
Additionally, by reducing a product’s water content, freeze-drying aids in extending a food’s shelf life because decreased water activity prevents the growth of most bacteria, yeasts, and molds.
This is crucial for fresh plant-based foods, which might not always be available.
Last but not least, by eliminating the water content from a product, its volume and weight is lowered, making it simpler to handle, store, and transport.
Reference: Novel ingredients based on grapefruit freeze-dried formulations: Nutritional and bioactive value
What Foods can be Freeze-Dried?
For hiking, camping, space exploration, emergency and survival applications, and military rations, freeze-dried foods are frequently employed. Due to their portability, ease of preparation, lightweight, and long shelf life, they are preferred over traditional cuisine.
While the majority of freeze-dried foods are made from plants, this technique can be used to preserve a variety of foods.
Some foods that can be freeze-dried are listed below.
Fruits: blackberries, bananas, pears, oranges, strawberries, apples, and fruit purée.
Almost all veggies, including tomatoes, carrots, asparagus, mushrooms, peppers, and pumpkin
Beef, fish, chicken, eggs, pig, turkey, and shrimp are among the meats.
Rice, beans, pasta, quinoa, polenta, and other grains
Whole meals like Pad Thai, stews, chiles, and snacks are available frozen.
Drinks: milk, juices, coffee, tea, and instant coffee
Garlic, mint, basil, ginger, oregano, and other spices
Sweeteners: powdered sugar and maple syrup
What are the Possible Drawbacks of Freeze-Drying?
A great way of food preservation is freeze-drying. There are a few possible drawbacks to take into account, though.
First off, although removing water from a product inhibits microbial development, disease-causing bacteria in raw foods can endure drying and persist throughout storage. When consumed, they can result in foodborne illness.
So, before being freeze-dried, foods that must be cooked before consumption must also be cooked.
Second, while freeze-drying preserves the antioxidant content of foods, the high porosity of these goods makes it simple for oxygen to enter, which could result in increased levels of oxidation or degradation of bioactive chemicals.
Can Food be Freeze-Dried at Home?
Equipment that is specialized, frequently expensive, and that operates at a particular temperature and pressure is needed for freeze-drying.
If you don’t want to spend the money on a home freeze-drying machine, you may still freeze-dry goods at home by using the freezer method.
The instructions for using the freezer method are listed below. Even though it doesn’t need any special tools, it takes the longest.
Cook, dry, and wash the food as needed.
Cut it as evenly and into 1-inch squares as you desire. It is better to stay away from huge pieces of food.
Put the food on a tray in a single layer, then put the tray in your freezer. The proper freeze-drying of food in the freezer will take around a week.
Take a bit of your food out of the freezer, then let it defrost to check how it is doing. If it changes back to its original hue, the procedure is finished. However, if the food turns black or dark brown after thawing, the freeze-drying process wasn’t complete.
Frozen meals should be kept in sealed containers.
How does Fruit that has been Frozen-Dried Taste?
Imagine the ripest fruit turning from delicious and velvety to airy and crisp. The flavor of freeze-dried fruit is remarkably similar to that. It is the dried form of popular fruits, such as strawberries, raspberries, apples, bananas, dragon fruits, kiwi, blues, pineapple, and other sweet fruits, during the peak season. Since freeze-drying retains flavor far better than dehydration, the flavors are brighter and more intense. Fruit that has been frozen and dried has a rough, dry, and crispy texture that gives it a satisfying crunch when you bite into it.
Why do People Use Freeze Dryers?
In order to transport blood, serum, and penicillin during World War II, freeze-drying was first widely used. Lyophilization technology has advanced since the creation of these contemporary freeze-drying methods and has been put to use in a wide range of industries. Research in the biological and environmental sciences, as well as the creation of many contemporary pharmaceuticals, frequently uses laboratory freeze dryers.
The most typical usage of lyophilizers in the household is to freeze dry goods. In addition to extending the shelf life of foods, this method of preservation has been demonstrated to lock in vital nutrients and improve the flavor of items like fruits, vegetables, meats, and even coffee.
What are the Different Stages of Freeze Drying?
The lyophilization procedure consists of three steps: pre-freezing, primary drying, and secondary drying.
The most crucial step in the freeze-drying process is the pre-freezing phase. The sample material will need to be cooled to a minimum of the sample’s melting point at this stage. By doing this, you may be confident that the sample will be thoroughly frozen and ready for sublimation. The sample won’t obtain the same preservation qualities as with sublimation if it isn’t frozen solid since evaporation will take place.
When you turn on your freeze dryer and vacuum pump, primary drying starts. As a result of the low atmospheric pressure, the sample starts to cool through evaporation, which releases heat to quicken the freeze-drying procedure. Approximately 93% of the water in the sample is sublimated out by the time primary drying is complete. Depending on the sample type and heat input, this stage may take several days. Primary drying is where the run would terminate for laboratories using their freeze-drying equipment for sample preparation and resuspension. The flow would proceed on to secondary drying so that the sample may be preserved for a long time.
Water molecules that have been bonded to the sample are released during the secondary drying process. In this phase, further heat is applied to remove extra moisture, leaving behind a moisture content of roughly 2%. Samples that are being prepared for long-term preservation and storage frequently use secondary drying.
Freeze drying, also known as sublimation, is a method of dehydrating frozen food that turns ice into vapor. It is a healthy way of food preservation since it keeps most of the nutrients and beneficial plant chemicals in foods, along with their color, flavor, and look.
It does not, however, eradicate dangerous microorganisms. As a result, cooking fresh foods is required before freeze-drying them. If you don’t have a home freeze-drying machine, you may easily freeze-dry your own food at home using your freezer.