-30C freezer or -20C freezer?

Model Organism: Worms Scientific Discussion
1

Our lab is trying to get a new freezer. There are two choices from Fisher Thermal: -30C freezer with automatic defrost and -20C freezer with manual defrost. I prefer to have a freezer with auto defrost function. The -30C freezer will warm up about 10 degrees when it does auto-defrost. So, in order not to warm above -20C, the -30C freezer is suggested to set at -30C. However, as a new tech in a worm lab, I don’t know if -30C is ok for the restriction enzymes/reagents/materials generally used in worm labs.
For example, restriction enzyme and its buffer are recommended to store at -20C. If we store them at -30C, I don’t if they are ok. Additionally, when -30C freezer does auto-defrost, it repeatedly warms up and cools down. I don’t if this will damage enzyme activity.
Thank you very much in advance for your suggestion.
Kim

2

I don’t know of a careful study of enzyme activity or stability, but I’ve seen a frost-free -30 Revco freezer work for storing lab samples, including enzymes.

Note though that in the freezer most enzymes (ie not the various kits in their little boxes) were buffered for temperature, stored in Eppendorf Isopacks, in a drawer-style microplate freezer rack (something like this). Very organized, very space efficient, rather expensive to set up (we got a bulk discount on a dozen Isopacks).

3

The air in defrosting freezers is very, very dry. If your tubes and samples are in air-tight tubes you should be okay, but I would be seriously concerned about evaporation/sublimation in frost-free freezers.

-Kevin.

4

Thank you very much for your inputs. It sounds like that we better to get a -20C freezer with manual defrost.

5

Just to echo some of what has been said and to add a couple of points.

I too think you would be better with a manual defroster…you decide when it defrosts and you control the temperature of your stored samples.
The defrost cycles on some freezers takes the temperature relatively high and that repeated over many times is a no no for your enzyme stocks etc.

Obviously with the manual defroster you need your back up -20 as a temporary storage space which I assume you have?

Steve

6

Thanks, Steve! We ordered the -20C freezer with manual defrost.