Everything You Need to Know about Freeze Drying

What is Lab Freeze Drying?

Freeze, or freeze drying, is a new technology that sublimates water in materials at low temperatures and pressures to dehydrate and dry them.

Freeze drying ensures that the original structure of the sample is protected to the greatest extent possible and is often used in areas such as preserving perishable materials or extending the shelf life of products. You can control the drying speed and time by adjusting parameters such as temperature and vacuum so that the whole drying process can be completed efficiently.

Structure of Lab Freeze Dryer

How does freeze drying work?

⒈. Pre-freezing

The substance to be dried is first frozen to a low temperature so that the water inside it forms ice crystals. Preparing for the sublimation process that follows. This is a very critical stage of the freeze-drying process. Freeze-drying is most easily achieved using large ice crystals, which can be produced by slow freezing or annealing. However, in the case of biological materials, when the crystals are too large, they may break down the cell walls, resulting in less-than-optimal freeze drying. To prevent this, the freezing process should be carried out quickly. For materials that settle easily, annealing can be used. The process consists of rapid freezing and then raising the product temperature to allow crystal growth.

2. Primary Drying

In this process, the ice sublimates without melting. This process removes 95% of the water. The main principle of operation is to reduce the pressure and heat the material to sublimate the water.

3. Secondary Drying

The material continues to be heated under vacuum to remove the residual water. Most materials can be dried to 1-5% residual moisture. This step is performed by slowly increasing the temperature, but keeping it at a low temperature to avoid thermal denaturation of the material. This step is important to preserve the stability of the sample.

Lab Freeze Drying Applications:

1. Foodstuffs: used for freeze-drying of foodstuffs, coffee, alcohol, fruits and vegetables, to maximally maintain the form, flavor as well as nutrients of foodstuffs.

2. Pharmaceutical manufacturing industry: maximally maintains the activity of drug products, heat sensitivity, suitable for long-distance transport and preservation.

3. Laboratory: freeze-drying preservation of microorganisms, viruses, polymer materials, insoluble substances as well as enzymes, extraction and drying of proteins.

4. Environmental field: freeze-drying of tissues of insects, plants and animals, as well as freeze-drying of soil and mud pollution samples.

How to choose a lab freeze dryer?

a. Freeze-drying area

According to the number of samples to choose the appropriate size of the drying chamber, enough freeze-drying area to ensure uniform drying of the sample improves drying efficiency.

b. Cold trap temperature

A cold trap is a device to capture water in the freeze drying process. Theoretically, the lower the temperature of the cold trap, the stronger the ability of the cold trap to capture water. However, the low temperature of the cold trap, high requirements for refrigeration, machine costs and high operating costs. The cold trap temperature of the experimental series freeze dryer mainly has several grades such as around -45℃, -60℃ and -80℃. In the absence of special needs, the cold trap temperature of about -60℃ is the ideal choice.

c. Cooling rate

The cooling rate reflects the cooling capacity of the refrigeration system, in the case of no load, the cold trap temperature should reach the lowest temperature specified in the index within 1 hour. For example, the cold trap temperature ≤ -60 ℃ of the freeze dryer, the machine from the opening of the refrigeration to start timing, and the cold trap temperature to reach -60 ℃ time should not be greater than 1 hour.

d. The performance of the small freeze dryer needs to be considered. Performance includes freezing speed, vacuum and temperature control function. According to the performance indicators, weigh the choice according to the actual needs.

e. Control system: the control system should have a stable and reliable performance, able to accurately control the freezing, vacuum and drying temperature and other parameters

Laboratory Freeze Dryer Recommendation

Flagship

Mainstream

Economy

Problems to avoid during freeze drying

Excessive heating temperatures may cause the product to remelt or collapse, or overload the condenser as a result of too much steam impinging on it. The following are factors that may cause these problems:

1. Excessive vapour generation

2. Surface area too large

3. Condenser area too small

4. Insufficient refrigeration

Vapour suffocation - vapour is being produced faster than it can pass through the vapour port (the port between the product chamber and the condenser), resulting in increased pressure in the chamber

Commonly Used Freeze Drying Terms

Eutectic Point or Eutectic Temperature:

The temperature at which the product exists solely in the solid phase, representing its minimum melting temperature. Note that not all products have a eutectic point, and some may have multiple eutectic points.

Critical Temperature:

The highest temperature a product can reach during freeze drying before its quality starts to degrade due to melt-back or collapse.

Crystalline:

1. The material forms crystals when frozen.

2. Has a eutectic point or multiple eutectic points.

3. Fast freezing creates small crystals that are difficult to dry.

4. Annealing can help form larger crystals.

Amorphous:

1. Multi-component mixtures that do not crystallize and do not have a eutectic point. Instead, they turn into a 'glass.'

2. Does not have a eutectic point.

3. For amorphous materials, freeze drying must be performed below the glass transition temperature.

Collapse:

The point at which the product softens to the extent that it can no longer support its own structure. This can lead to several issues:

1. Loss of physical structure

2. Incomplete drying

3. Decreased solubility

4. Significant ablation (splat)