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A Complete Introduction of Vacuum Freeze Drying

A Complete Introduction of Vacuum Freeze Drying

As per social development and technology upgrade, freeze dried products are everywhere around us, although it is the most expensive dehydration method. Freeze drying technology is more and more popular, not only because of the vast application (nearly all industries), also because of the incomparable dried quality.

Knowledges of Freeze Drying

Many people heard of freeze drying, or tasted freeze dried products (Food, pharmacy, fruit etc.), but don’t know how it was produced. In this article, we will give a complete introduction of freeze drying include:

  1. Freeze drying fundamental definition.
  2. Process of freeze drying.
  3. Application fields.
  4. Advantage and disadvantage.

Freeze Drying Fundamental Definition

Freeze drying is a low temperature dehydration process, removing products’ moisture by freezing the material, and then reduce the surrounding pressure to allow the frozen water in the material to sublime directly from solid phase to gas. That means, most of the drying processes will be finished in minus temperature.

Therefore, freeze drying has less impact on product and is famous for drying products without damage them. Result it works extremely well on almost all industries and is considered to be one of the best ways to dry products.

Water Triple Point Graphic

Water Triple Point Graphic

Tips: Freeze drying theory based on water triple point graph, that is: under water triple point pressure 610.5Pa, no liquid water exists, solid ice can sublimate directly to vapor if any heat energy provide.

In pharmaceutical area, freeze drying called lyophilization. Lyophlized drugs have very high rate in market, they are easy to transport, light weight, high bioactivity after rehydrate and no need critical storage environment. Thus, for some drugs, lyophilization is the primary choice, for example, penicillin.

Process of Freeze Drying

Because of the fundamental principle of freeze drying is sublimation: a water remove process based on freezing the raw material, and then reduce frozen product surround pressure to enable the water boiling point reduce, solid ice will direct sublimate to vapor. By this, the water in product success removed.

So, freeze drying process involves 3 main stages: Freezing, Primary Drying (Remove physical water) and Secondary Drying (Remove Bound Water)

Freezing Stage:

The freezing step is the most important and critical in the whole freeze drying process. Because incomplete frozen product can be boiled and spoiled under vacuum environment. For products complete frozen, you may need find out the product’s eutectic point. Keep in mind that freezing step guarantees the final products' form.

Primary Drying Stage:

The primary drying step is to remove physical water from material. During this stage, pressure is lowered to a few mbars and proper heat is supplied to the material, so that there is enough energy for water to sublimation. In this stage, >95% water will be removed. So, Primary drying aim to remove physical water.

Primary drying takes longer time (several hours to several days) because you need add heat gradually. Too much heat add to material in a short time will cause melt. As well as, the vacuum degree, which can speed the sublimation need set considered.

Secondary Drying Stage:

The secondary drying step aims to remove bound water molecules. In this phase, more energy and high vacuum will be applied. Higher temperature (can be above 0C) and lower pressure (<30Pa) to encourage desorption. Secondary drying remove bound water effectively.

Freeze Drying Process: Freezing Step

Freeze Drying Process: Freezing Step

Freeze Drying Process: Drying Step

Freeze Drying Process: Drying Step

Application Fields

Freeze drying works perfect on almost all industries, some have been tested and applied, some are still researching. The most matter is freeze drying no strict request of raw material form, it can be entire, particle, liquid, slice, pulp or pasta. Here are some most popular application areas.

  • Food freeze drying: Fruit, vegetables, cooked meals, instant coffee, seafood, pet food, meat, soup and so on.
  • Dairy industry: Milk, yogurt, ice cream, formular milk powder, cake etc.
  • Pharmaceutical: APIs, vaccines, capsules, penicillin, herbs etc.
  • Biological: Tissues, specimen, blood, probiotics etc.
  • Nutraceutical
  • Documents
  • Floral

Too many items can be freeze drying, if you are not sure, please contact us. Our specialists always ready to share knowledges.

Fruit Freeze Drying

Fruit Freeze Drying

Vaccines Freeze Drying

Vaccines Freeze Drying

Pet Food Freeze Drying

Pet Food Freeze Drying

Advantage and Disadvantage

The most important advantages of freeze-drying are listed below:

  1. Minimum damage to the material. Specially fit heat sensitive product.
  2. The nutrition, taste, flavor and vitamins are remained.
  3. Keep product original structure. Porous and friable structures is created after water remove.
  4. Fast and complete rehydration guarantee.
  5. Easy storage and long shelf life. Dried product can store at room temperature, no need refrigeration. Shelf life more than 20 years.
  6. Freeze drying material not shrink or toughen.
  7. Freeze drying especially fit product that meets one or more of the following criteria:
    • It is perishable or unstable.
    • It is heat sensitive.
    • Valuable product.
    • Dried product needs quick and complete rehydration.
    • Due to store or transport need, material needs light weight and accept a wide range of storage temperature.

Disadvantages of freeze drying also obvious:

  1. Cost too much. Among all kinds of drying methods, freeze drying is on the top. This is because of the very slow sublimation speed, too much electric consumption and longer drying time.
  2. Batch production.
  3. Longer drying time. Typically need 14~24hrs for a batch, some products may take a few days.
  4. Some product: high fat or high sugar contain not easy to freeze dry, and some product like beef, freeze dried quality almost same with vacuum drying, but higher cost.

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