Freeze drying (FD): utilizing the sublimation principle in physics. First, freeze the material to several tens of degrees below zero (turning water into ice), and then place it in a vacuum environment. Without going through a liquid state, let the ice turn into water vapor and escape directly. This is like pulling away the "ice skeleton" that originally supported the material, leaving behind a porous empty shelf.
Drying: utilizing heat convection. Blow the material with hot air to "dry" the water, causing the liquid water to turn into a gaseous state and evaporate. It's like drying clothes, using heat to force water out.
2. Finished product quality: one is "black technology" and the other is "traditional craftsmanship"
This is the most intuitive difference between the two, which directly determines the price and grade of the product:
Appearance and Form:
Freeze drying: Because it is dried in a frozen state, the physical structure of the material is supported by an "ice skeleton", so the volume remains almost unchanged after drying, and the interior has a sponge like porous structure. For example, freeze-dried strawberries look as big as fresh strawberries and have bright colors.
Drying: When water evaporates, surface tension is generated, causing severe shrinkage, deformation, and drying of the material. For example, dried strawberries will shrink into a ball and turn dark and black in color.
Nutrition and activity:
Freeze drying: The entire process is carried out at low temperatures (below 0 ℃ or not exceeding 40 ℃), which can retain more than 95% of thermosensitive nutrients such as vitamins, proteins, and biological enzymes.
Drying: High temperatures (60-120 ℃) can damage a large amount of nutrients, especially vitamin C and active substances, causing severe loss. Experiments have shown that the nutrient retention rate of freeze-dried strawberries may be more than three times that of dried strawberries.
Taste and rehydration:
Freeze drying: Loose and porous, with excellent rehydration properties, it can absorb enough water and restore its original state in just a few seconds when thrown into water; It tastes crispy (like freeze-dried yogurt chunks).
Drying: The texture is tight and hard, difficult to soak, and often has a chewy texture or is as hard as "firewood" when eaten.
3. Cost and efficiency: one is "noble" and the other is "common people"
Freeze drying: The equipment is very expensive (requiring vacuum system, refrigeration system, heating system), and the drying cycle is long (may take more than 24 hours), with high energy consumption. So freeze-dried food is usually more expensive.
Drying: The equipment has a simple structure (mainly consisting of heating tubes and fans), low technical threshold, fast drying speed, and low cost.
4. Applicable scenarios
Freeze drying: suitable for high value-added, heat sensitive products. For example: vaccines, antibiotics, high-end skincare products, freeze-dried fruits (strawberries, durians), instant coffee, pet raw meat and bone.
Drying: Suitable for bulk products with low requirements for nutrition and appearance. For example: wood, medicinal herbs (partially), preserved fruits, feed, industrial raw materials.
💡  Tips for avoiding pitfalls
If you buy "dried fruits and vegetables" in the market, be sure to distinguish:
Real freeze-dried foods usually only have the fruits/vegetables themselves on the ingredient list, with a crispy texture that crumbles with just a pinch.
Many cheap "dried fruits and vegetables" are actually VF (vacuum low-temperature frying) or hot air drying, and the ingredient list usually includes vegetable oil, sugar, or salt, which tastes oily or tough.

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