VERIFIED CONTENTAuthor: Aleksandra Żyłowska-Mharrab, dietitian, food technologist, educator
Freeze drying is one of the methods of extending the shelf life of food. In addition, it is a new and little-known method, which makes many people suspicious of freeze-dried products. Find out what freeze-drying is and whether it affects the nutritional value of products. Is it worth reaching for freeze-dried fruit and vegetables?
Freeze drying is drying by freezing. Although drying is associated with the use of increased temperature and hot air flow, which allows the water to evaporate, the product can also be dried by freezing.
What is freeze drying?
During freeze-drying, water or other solvent present in the product freezes very quickly at low temperature. Quick freezing enables the formation of very small ice crystals, which do not damage the tissues of fruit and vegetables, i.e. they do not deteriorate their structure.
Water frozen in products is then transformed directly into gas - it evaporates. This phenomenon is called sublimation and it means the transition of a solid to a gas without the liquid state. Thus, during freeze drying, the frozen water is converted directly into water vapor. This technique is responsible for the excellent properties of freeze-dried food. However, it is very expensive.
Freeze drying is used primarily for drying biological materials, tissues, bacteria, vaccines and for the production of certain drugs or implants .
In food production, it was first adapted in the middle of the 20th century. Back then, freeze-drying was too expensive to simply produce food. Initially, freeze-drying was used to produce food products for the crews of spacecraft.
Freeze-dried products are considered to have the same properties as fresh products . Retaining characteristics such as shape, appearance, color, taste, nutrient content and biological activity make this technique one of the most fascinating processes for drying food materials.
The potential of freeze drying is huge. Nevertheless, freeze drying requires a longer drying time compared to traditional methods and its costs are very high.
Freeze-dried food instores
Currently, freeze-dried food is still not very popular, but anyone who thinks that they have never encountered a freeze-dried product is wrong. What's more, we see them every time we shop at a discount store.
This product is instant coffee. Instant coffee is produced by freeze-drying on a massive scale. In addition to instant coffee, you can often see freeze-dried herbs and spices in stores, instant ready meals to be poured with boiling water, and more and more often also fruits and vegetables.
The food segment in which freeze-dried products can be found most often is food for sportsmen and travelers. It meets the three most important conditions - it is very durable and very light, and at the same time nourishing. Freeze drying is recommended for drying food products that are not very resistant to high temperature due to their structure and the content of bioactive compounds.
Under the influence of traditional drying, there is a particularly large loss of vitamin C, tocopherols (vitamin E), carotenoids (vitamin A precursors) and antioxidant polyphenols. Foods with a high content of them lose their nutritional value very much.
In Poland, freeze-dried fruit can be bought in stores, most often in small string packages. They are offered as a he althy snack.
Freeze-dried are available:
- pineapples,
- raspberries,
- strawberries,
- blueberries,
- blackberries,
- gooseberry,
- aronia,
- cranberry,
- Are Acai Berries.
As it is easy to see, most of them are fruits that do not tolerate traditional drying very well and are not available for sale in dried form.
Producers also offer freeze-dried vegetable crisps (a brilliant alternative instead of crisps), and in online stores you can buy various vegetables such as:
- cauliflower,
- cabbage,
- broccoli,
- onion,
- kale,
- corn,
- green peas,
- carrot,
- cucumber,
- parsley,
- por,
- celery,
- and even a potato.
Freeze-dried vegetables are available as powder, grits, cubes, and sometimes, when the structure of the product allows, in larger pieces.
Certainly, however, the availability of freeze-dried vegetables is lower than that of freeze-dried fruits. At first glance, the lyophilisates of spices and herbs differ from their traditionally dried counterparts.
Basil, oregano, chives and dill have a more intense color and aroma. Interestingly, in the case of spices, the difference in the price of dried and freeze-dried onesit's not big at all. On average, 100 g of dried herbs costs PLN 15-20, and freeze-dried herbs PLN 18-30.
Considering that herbs and spices are used in cooking in gram amounts, and additionally freeze-dried ones can be used less, because they are more intense in flavor, the difference in price is very small.
Advantages and disadvantages of freeze-drying
Freeze drying, apart from the high price of the drying process, has basically only advantages. Freeze-dried food is of a very high quality, unlike traditionally dried food. The use of low temperature means that most of the chemical compounds in the dried product remain unchanged.
Proteins, vitamins, dyes, antioxidants and many other bioactive substances do not change its structure during freeze-drying, and very often there is no quantitative loss.
This is a huge advantage of freeze-dried food over warm air dried. During conventional drying, food mainly loses water-soluble vitamins (C and B), proteins, antioxidants and dyes are damaged. This significantly reduces the nutritional value of traditionally dried fruit and vegetables compared to fresh food.
Freeze drying causes very little loss of bioactive compounds compared to traditional drying, but it cannot be said that the biological activity of freeze-dried fruit and vegetables is always exactly the same as that of fresh ones.
The antioxidant activity of food products and the content of water-soluble vitamins sometimes decrease during freeze-drying. It depends on the freeze-dried food product and freeze drying parameters.
Traditional drying causes the color of the products to change as well. Many of them turn brown. The color of fruit and vegetables remains intact during freeze-drying. It is similar with taste and smell. However, the texture of the products changes. It becomes more porous, which may be disturbing for some people. It is also technologically unfavorable in the case of freeze-dried meat.
The constant state of water in food products at the time of sublimation starts means that the shape and size of the freeze-dried food hardly changes. A very big advantage of freeze-dried products is the fact that after adding water, it is easily reabsorbed into tissues. This means that by soaking, freeze-dried fruit and vegetables can be rehydrated much easier and more efficiently than products dried using other methods.
Freeze drying inhibits the activity of bacteria and enzymes in food products. This is due to the lack of availability of water that is therethe environment of bacterial development and the course of biochemical reactions. It also slows down the oxidation of fats. All this makes freeze-drying an excellent method of food preservation.
Are freeze-dried fruits and vegetables he althy?
Knowing what freeze-drying is, how this process works and how it affects the nutritional value of food products, we can say without hesitation that freeze-dried fruits and vegetables are he althy. Freeze-dried vegetables become a vitamin bomb.
Very small amounts of water-deprived vegetables concentrate vitamins, antioxidants and fiber that are valuable for he alth. Freeze-dried vegetables are a vitamin shot, but in a solid form.
What about fruit? In the case of freeze-dried fruit, the same could be said if it were not for the sugar content. After removing the water from the fruit, the sugar content per 100 g, and therefore the calorific value, increases many times over.
For example, a handful of fresh strawberries weigh 70 g, contain 4.1 g of sugar and 23 kcal. A handful of freeze-dried strawberries weighs 15 g, but has 8.4 g of sugar and 49 kcal. 100 g of fresh strawberries is 5.8 g of carbohydrates, 1.8 g of fiber and 33 kcal, and freeze-dried strawberries - 56 g of carbohydrates, 19 g of fiber and 328 kcal. Thus, the content of sugar and calories in the lyophilisate increases tenfold.
For this reason, freeze-dried fruit cannot be eaten in uncontrolled amounts, because it is very easy to unknowingly eat with them a portion of simple sugars contained in a chocolate bar.
Although, if we compare the he alth effects of eating a chocolate bar and eating a large amount of freeze-dried fruit, fruit will of course be many times he althier, because apart from sugar, they provide a lot of vitamins, antioxidants and fiber. Remember, however, that fiber needs water to benefit the body. When eating freeze-dried fruits and vegetables, you should drink them with water to avoid constipation.
Why choose freeze-dried fruits and vegetables?
Freeze-dried fruit and vegetables retain most of their nutritional value compared to fresh produce. Freeze drying is the best method of preserving nutritional value among the methods of extending the shelf life of food.
Freeze drying allows you to keep the original shape, taste and color of fruit and vegetables, and their texture only slightly changes.
Freeze-dried fruit and vegetables can be stored at room temperature for a very long time. Freeze-drying itself is a sufficient method of extending the shelf life of food. No preservatives are added to freeze-dried fruit and vegetables and can be stored safely dryfor up to 25 years!
Freeze-dried products are very light due to the lack of water, and at the same time contain a lot of fiber. This makes them a great, nutritious snack that is easy to take with you.
Why freeze-dried and not frozen or canned?
We already know that freeze drying has a huge advantage over traditional drying. The quality of freeze-dried fruit and vegetables is much better than the dried ones. How does it compare with frozen foods and canned food?
Frozen foods, right after freeze-dried products, are the most effective form of preserving the nutritional value of food. Skillful freezing allows for really good storage of vegetables and fruit for about a year. Care must be taken to freeze dry vegetables and fruits and not to allow them to defrost again, so that the frozen food remains loose and not lumpy. The main problem during freezing is the loss of water-soluble vitamins, deterioration of shape and consistency.
During freezing, large ice crystals are formed, which break the tissues of the products. This is why we often have a blueberry stick after defrosting, and not single, firm fruit. The fruit juice leaks, and with it the water-soluble vitamins are lost. Well-frozen vegetables and fruits lose about 20% of their vitamins.
However, freezing is a cheap method of storage, which allows you to preserve most of the he alth and taste of products. The advantage of freeze-dried products over frozen foods is higher nutritional value, ease and longer storage time and the possibility of simple use as a snack.
Canned fruit and vegetables are also an alternative when we do not have access to fresh produce. Preserving, however, raises the most doubts. Manufacturers usually add large amounts of s alt and sugar to canned vegetables and fruit, which has a negative effect on their he alth.
In addition, bisphenol A (BPA), which is harmful to he alth, penetrates from food cans, and the losses of vitamin C and group B are greater than during freezing. With a choice of canned and frozen foods, the frozen one is the he althier choice. And the he althiest of all the available forms of extending the shelf life are lyophilisates.