Cryostat – FAQ – Frequently Asked Questions

Frost consists of tiny ice crystals formed when moisture in the air freezes directly on a cold surface. Ice, on the other hand, results from liquid water freezing into a solid state. In cryostats, frost commonly forms due to humidity in the air coming into contact with cold components.

Humidity always freezes at the coldest point in the chamber. The quick-freeze shelf is the coldest area, particularly when two freezing stations are active. The temperature at this location is approximately 10 °C lower than the chamber temperature, making it the primary spot for frost accumulation.

Complete prevention is not possible. You can minimize frost formation though:

• Keep the window closed when not cutting.
• Avoid heavy exhalation into the chamber.
• Schedule nightly defrost cycles via software.
• Manually defrost when significant ice buildup occurs.
• Ensure proper installation conditions (e.g., maintain distance from walls, avoid placement under air conditioning units, perform regular maintenance as per the user manual).

If the QFS were defrosted, the frost would turn into water. When cooling resumes, this water would freeze into solid ice, which is much harder to remove than frost. Additionally, the QFS is used for overnight storage of samples, which would thaw if defrosting were applied.

Automatic defrosting is programmed via software to be applied every night for approximately 30 min, melting ice from the evaporator in the cooling chamber. This improves cooling efficiency, but the rest of the chamber remains well below freezing and is not being defrosted.

Manual defrosting happens by hand. The device is switched off and allowed to warm up to ambient temperature, either overnight or accelerated with a hairdryer. The chamber window must remain open to allow humidity to escape.

The cooling chamber operates at extremely low temperatures (as low as down to -30 °C), while the area above the chamber, where the glass panel is positioned when open, remains at room temperature. If cold air seeps into this upper area, the temperature drops slightly, causing condensation to form. Solutions include to:

• Increase the chamber temperature slightly.
• Raise the room temperature.
• Reduce the humidity in the room.

• Extremely low temperatures can make the freezing medium more brittle, leading to poorer cutting results.
• In samples with high water content, excessive cold can accelerate ice crystal formation, making sections fragile and prone to breaking.

The internal mechanisms and components are adjusted perfectly to working conditions. The handwheel can be used comfortably and without tolerance when the device is cooled down and ready for operation.
The device should therefore be cooled down to operating temperature for a few hours, ideally overnight for at least 8 hours.

If the device is supposed to reach a certain temperature in a desired time (usually as quickly as possible), this is not of value, as this only reflects the temperature of the air inside of the chamber. However, when cooling down initially, all appliances in the chamber must be cooled down completely. This takes longer than just cooling the chamber down. We recommend cooling down for several hours, ideally overnight for at least 8 hours.

If you keep the accessories in the chamber, they will have the same temperature as the sample. This enables a better result when cutting the specimen and picking up the section. Additionally, it reduces condensation inside the chamber as no warm items will be brought in. It is highly recommended to keep the specimen holders inside of the cooling chamber anyway, to improve and fasten the freezing process.

The rear freezing positions are closer to the evaporator that cools down the chamber. The temperature in this area is slightly colder than in the front freezing positions.

When cutting particularly difficult samples, object cooling might be helpful. The specimens are additionally cooled down by the object cooling, and a separate temperature setting is possible. This also actively reduces the frictional heat that occurs during cutting.
The object cooling is primarily used for fatty tissue, tissue with high percentage of water or tissue with bad integrity. Examples are: lymph nodes, cysts, breast.

Disinfection using the optional UV lamp has the advantage that it can be started via the menu. It then requires no further intervention or work by the user. It reduces the amount of work for the laboratory staff and minimizes the physical contact with potentially dangerous tissue.
It also offers process reliability, as disinfection using the UV lamp follows strict rules and is always carried out in the same way.