Many people think of dehydration and freeze-drying as the same thing. Not really, they are very different. The following explains the specific differences between these two food preservation technologies.
Dehydrated vegetables, also known as rehydrated vegetables, are dried vegetables made by washing and drying fresh vegetables to remove most of the water in the vegetables. What is the difference between freeze-dried and dehydrated vegetables? With the continuous development of technology, there are many ways to dry vegetables, including drying, freeze-drying, microwave drying, sun-drying, etc. Freeze-dried vegetables are also a type of dehydrated vegetables.
Freeze-drying technology is a processing method of vegetable drying technology. Traditional drying methods are carried out at temperatures above 0°C or higher. The products obtained by drying are generally reduced in volume and hardened in texture. Some substances are oxidized, most of the volatile components will be lost, and some heat-sensitive substances, such as proteins and vitamins, will be denatured. Microorganisms will lose their biological activity, and the dried substances will not easily dissolve in water. Therefore, the dried product has a great difference in properties compared with that before drying.
The principle of freeze-drying is well understood. First, put fresh fruits and vegetables in a freeze-drying machine at about minus 50°C for freezing. After the fruits and vegetables are frozen, vacuum the drying box. After the vacuum is formed, increase the temperature slightly. The ice in the fruits and vegetables sublimates directly into water vapor and leaves the fruits and vegetables, while the remaining fruits and vegetables remain the same in volume and loose and porous. The moisture that can be removed by freeze-drying can reach more than 95%. The freeze-drying technology is basically carried out at a temperature below 0 °C, that is, in a state where the product is frozen. Until the later stage, in order to further reduce the residual moisture content of the product, the product is raised to a temperature above 0 °C, but generally not more than 0 °C. 40°C. Therefore, freeze-drying technology is a processing method with the lowest damage to vegetables.
Freeze-drying technology is carried out at low temperature, such as proteins, microorganisms, etc. will not denature or lose biological activity. When drying at low temperature, the loss of some volatile components in the substance is very small, which is suitable for drying some chemical products, medicines and food.
During the freeze-drying process, the growth of microorganisms and the action of enzymes cannot proceed, so the original properties can be maintained. Since it is dried in a frozen state, the volume is almost unchanged, the original structure is maintained, and no concentration phenomenon occurs. Since drying takes place under vacuum with very little oxygen, some oxidizable substances are protected. Drying can remove more than 95-99% of the water, so that the dried product can be stored for a long time without deterioration.
The difference between freeze-drying dehydration technology and drying dehydration technology:
Drying and dehydration process
No matter what method of food preservation is used, moisture needs to be removed. Dehydration is the most commonly used method. Dehydration has been a way of keeping food fresh for thousands of years, dating back to at least 12,000 BC. The Romans and Middle Eastern people used to put fruits and vegetables in a house, then fire roasted and smoked them to make dry food.
Modern dehydration technology has made it simple to use machines to circulate hot and cold air through food. This removes most of the moisture. The temperature is controlled to a level sufficient to remove moisture but not to cook the food. Dehydrated food wilts and becomes hard.
Freeze drying process
Freeze drying is a relatively new modern preservation process. It should be known, however, that you cannot freeze dry yourself at home without technical equipment. Some reports say freeze-drying originated in the Inca Empire. But more reliable sources show that freeze-drying was invented during World War II, when it was used to preserve blood plasma, medicines, and later aviation food.
The lyophilization process is relatively simple. Food is placed on large shelves inside the vacuum chamber. The temperature drops below freezing and then gradually increases. Moisture in food is converted from solid form to gas, thus preserving food structure and nutritional value.
The difference between freeze-dried dehydrated vegetables and dried dehydrated vegetables:
1. Moisture
The main goal of food preservation is to remove moisture so that food does not spoil and grow mold. Dehydration removes 90-95% of the water while freeze drying removes 98-99%. Dehydrating food yourself at home usually leaves 10% humidity, but professional dehydration is more thorough and therefore has a longer shelf life.
2. Shelf life
Moisture removal rate directly affects shelf life. Dehydrated foods like dried fruits, vegetables, and powders have a shelf life of about 15-20 years; dehydrated foods like honey, sugar, salt, hard wheat, and oats have a shelf life of more than 30 years. On the other hand, frozen dehydrated foods have a longer shelf life, such as dried fruits and vegetables, which can last for 25-30 years.
3. Nutrients
Freeze-drying retains most vitamins and minerals, according to a study by the U.S. Institute of Health. But compared with fresh fruits and vegetables, freeze-dried foods lack some vitamins, such as vitamin C, which breaks down faster. Dehydration does not change dietary fiber or iron content. However, dehydration breaks down vitamins and minerals during the preservation process, so the nutritional value is not as good as freeze-dried foods. Dehydration can lead to the loss of vitamins A and C, niacin, riboflavin and thiamine.
4. Appearance and structure
One of the main differences between dehydrated and freeze-dried foods is the appearance. Dehydrated food will become brittle and hard, while frozen dehydrated food will become soft immediately in the mouth. Weight is another difference. Freeze-dried foods are much lighter in weight than dehydrated foods.
5. Cook
Dehydrated foods need to be cooked and eaten. Many times, they also need to be seasoned. This means that it takes time to cook the product in hot water and eat it after cooling. Preparing dehydrated food takes between 15 minutes and 4 hours. However, only boiled water is required for freeze-dried food. Add hot or cold water and wait at least 5 minutes before eating.
6. Price
In general, dehydrated foods are cheaper than cold-dried foods. Freeze-dried and dehydrated foods have their pros and cons, and if you're on a tight budget, dehydrated foods are clearly the better option.
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