Pressure cooker

At Mediamatic we have several pressure cookers to sterilize our materials.


22l pressure cooker - making spawn Marieke Broertjes

In general:

  • ALWAYS use the inlay; never place glass directly on the bottom. Glass might break! 
  • Use enough water; when the pan cooks dry, your materials will burn and the pan might even explode. Make sure the safety valves are not blocked and the lid is on correctly. Double check. Be careful! ( happened, glass everywhere)
  • The longer you have to cook, the more water will evaporate. Take this in account. 1/4 to 1/3 volume of water should be good. If your samples seem to drown; just place a plate or a brick under the inlay to elevate.
  • ALWAYS loosen the caps from bottles and jars before you place them in. The pressure can cause them to explode. You can protect filters etc with aluminum foil over the lid of your jar.

So... Check list:

  1. Everything is in.
  2. Enough water.
  3. Valves ok.
  4. Caps loose.
  5. Lid on.
  • Start heating up the pan.
    When the hissing from the valve or pressure regulator starts; your pan is almost on pressure.
    It should be 15 psi (if you have a indicator) or if you put a drop of water on the lid, it should evaporate vigorously in seconds. 
  • Start timing!
  • If there is too much steam or even water escaping you can bring down the temperature a bit, but don't loose your pressure.
  • If you lost pressure: pick up the timing again (so extra minutes for the lost time)
  • Shut down the heat and let cool down naturally.

DO NOT try to speed up the releasing of the pressure by removing the regulator or pressing a valve...very tempting...But it will cause a very heavy boil inside the pan and your flasks. You can loose half of your agar by over boiling by this.

  • After the pressure is released you can remove your materials.
  • Agar needs to cool down to be able to pour. You can speed it up by swirling in a bucket of cold water. Keep it moving...

6l (BK)
This one is for small things and single bottles.
Use on small electric plates

22l (Presto - Homegreen)
Good working with pressure indicator.

Special instructions for spawn making (10L)

Note: It looses 1 liter water per hour of cooking

  • Elevate the inlay with a deep plate
  • Put 4 1/2 liter of water in the pot
  • Place the growbags, try to keep them clear from the walls
  • Put a plate on top to protect the top of the bags 
    Make sure the filters do not get wet!
  • Use a gas stove, but not the big butane burner (this one damages the pan)
  • Remove the pressure regulator
  • Bring to a boil
  • Place pressure regulator
  • Bring to 15 psi (regulator starts rocking and hissing)
  • Tune the fire so that it exactly 15 psi
  • Keep it there for 2 hrs
    Note: With more spawn it might be necessary to cook longer. Also, it might not fit.
  • Stop and cool down naturally

DO NOT clean with chemicals like Oxiclean. It eats the aluminium. Just boil for some time with water to get burned stuff off.

50+l (Chinese shop)
It is a bit warped and leaking. Not sure if it can reach the right pressure. No indicator. The sterilisation tape turns black after 3 hrs.
DO NOT use for spawn and sensitive materials.

INFO: Regularly treat the rubber parts with vaseline to keep them soft!