How to autoclave autoclavable cryo tubes without damaging them

Autoclaving is one of the fastest and most reliable ways to make lab tubes clean enough for reuse, but it is also where many cryo tubes get ruined. One wrong temperature, a cap left fully sealed, or a hasty cooldown can leave you with cracked, warped, or still-contaminated tubes and a bench full of wasted samples. The good news is that properly built autoclavable cryo tubes are designed to survive the whole cycle. Do it the right way and you can reuse them many times; get it wrong and you will be ordering replacements before your next experiment. Here is a clear, step-by-step guide to autoclaving cryo tubes without damaging them.

Step 1: Confirm the tubes are truly autoclavable

Before anything goes into the chamber, check what your tubes are actually made of. A cryo tube body needs to stay stable at 121°C, which in practice means polypropylene (PP). Polypropylene cryogenic tubes are heat-resistant, and responsible manufacturers mark autoclavable tubes with a PP symbol on the bottom or label. Tubes made of polystyrene or other low-heat plastics will warp and crack under autoclave conditions, so never assume, always check the material code. MGG molds all of its autoclavable cryo tubes from medical-grade PP, so they keep their shape through repeated cycles.

Step 2: Prepare each tube before loading

• Empty every tube and rinse it with purified water. Leftover sample residues can solidify under heat and are hard to remove later.
• Peel off paper labels. They may separate in steam, clog the machine, or leave sticky residue on the plastic.
• Loosen each cap by about a quarter turn. A fully sealed tube builds internal pressure and can pop its cap or deform its walls.
• Do not fully remove the cap either. A completely open cap re-exposes the clean interior to the autoclave environment and defeats the purpose of sterilization.

The cap, gasket, and thread matter as much as the tube body. If your tube uses a silicone gasket, check that the seal is still intact before each run; a worn gasket is the most common cause of leaks in a leak-proof cryotube after autoclaving.

Step 3: Load the autoclave with room to breathe

Steam needs to circulate around every tube to sterilize it evenly. Stand the tubes upright in a PP tube rack and leave gaps between them, and make sure nothing touches the chamber walls or floor, which stay hotter than the rest of the load. Overloading is one of the most common reasons tubes come out partially sterile, so when in doubt, run a smaller load.

Step 4: Run the correct cycle

For polypropylene cryo tubes, a standard gravity steam sterilization cycle is enough: 121°C at about 15 psi for 15 to 20 minutes. Larger tubes, such as 5 ml or 10 ml models, benefit from the longer hold time. Use a liquid cycle rather than a dry cycle so the heat transfers through moisture instead of blasting dry air onto the plastic, which can stress the surface. The temperature matters more than the length of the run; pushing the temperature higher to save time is exactly how tubes get warped.

Step 5: Cool down slowly and dry properly

The moment the cycle finishes is when the most damage happens. Never open the door immediately, and never release the pressure by cracking the door. Let the autoclave cool naturally, and let the tubes ｄｒｏｐ below about 80°C before you open it. A sudden ｄｒｏｐ in temperature, sudden pressure release, is thermal shock, and even a well-made tube can crack from it. Once the chamber is safe to open, remove the tubes on a clean bench, let the remaining condensate evaporate, and store them in a closed, dust-free container so they stay sterile until use.

Step 6: Inspect before every reuse

After the tube has cooled, hold it to the light and check for hairline cracks, warping, or yellowing. Cracks are easy to miss on an opaque or frosted tube, so turn it slowly and look at the thread and the base where stress concentrates. If you see any damage, discard the tube, do not reuse it. An intact cryo tube can be autoclaved many times, but a cracked one will leak at the worst possible moment, usually in liquid nitrogen.

Common autoclaving mistakes to avoid

• Sealing caps fully before loading, which leads to deformation or popped caps.
• Cranking the temperature above 121°C thinking it sterilizes faster.
• Crowding the chamber so steam cannot reach every tube.
• Opening the door right after the cycle and cooling the tubes too fast.
• Reusing tubes that show cracks, clouding, or a damaged gasket.

Final thoughts

Autoclaving does not have to be a gamble. Confirm the material, prepare the caps, load with space, run a controlled 121°C cycle, cool slowly, and inspect before reuse, and your autoclavable cryo tubes will serve you for many experiments. As a cryogenic tubes manufacturer, MGG produces polypropylene tubes built for exactly this kind of repeated sterilization, and every batch is checked for autoclavability and leak-proofness before it ships. When you need a tube you can autoclave with confidence, that is the kind of supplier you want behind your samples.