Freeze drying and drying
The difference between freeze drying and drying, which is better? The following freeze dryer manufacturers will discuss with you:
1. The difference between the working principle of freeze-drying and drying
Freeze-drying is the sublimation of water, and drying is the evaporation of water. The former is a solid-state directly into a gaseous state, and the latter is a liquid state into a gaseous state. The freeze dryer is a vacuum low-temperature drying equipment, which firstly freezes the moisture in the material into ice at a lower temperature, and then quickly heats it in a vacuum environment, so that the moisture in it is directly sublimated into a liquid state, and finally completes dehydration and drying. the goal of.
Drying, also known as thermal drying, is a drying process that uses a heat carrier and a wet carrier to cooperate with each other. Usually, hot air is used as a heat and wet carrier at the same time, that is, heating the air and then letting the air heat the sample, and the evaporated water from the sample is then absorbed by the air. Take away and discharge.
2. The nutritional difference between freeze-drying and drying
The process of freeze-drying can be regarded as the principle of physical sublimation. In order to maximize the preservation of the physical structure of the sample, the best method so far is freeze-drying at low temperature, because the physical structure of the sample is basically unaffected at low temperature and low pressure. It will not penetrate due to the humidity gradient existing inside and outside the cell wall, causing the surface pores to shrink or the internal water loss to dry out. And in a low-pressure vacuum state, the sublimation point is raised (towards normal temperature). Thereby, the sublimation process is accelerated and the drying efficiency is improved.
Compared with drying technology, freeze-drying technology can retain as many nutrients as possible in food, such as color, aroma, and taste, and effectively prolong the shelf life of food.
The effect of drying on the sample is that the temperature goes from the outside to the inside and the humidity goes from the inside to the outside (the opposite). And there is a limit to the speed, that is when the sample is at the extreme temperature that it can withstand. The maximum speed at which water diffuses from the inside to the outside. If the speed is too high, it will cause the skin to shrink and reduce the drying speed. If it is too slow, it will affect the efficiency. At the same time, if the temperature is too high, the internal water will vaporize too quickly, and it will not be able to be discharged through the capillary tube and expand, causing cell rupture.
Due to high-temperature drying, the drying method will cause the material to shrink and deform, and the nutrients will be greatly lost.
