Pressure Cooker Timing Calculator

Get the correct sterilization time for your substrate type, adjusted for altitude. Includes cooldown estimates and pressure cooker capacity.

Setup

Select your substrate, altitude, and pressure cooker size.

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Results

Sterilization time at 15 PSI.

01:30h:mm
Altitude Adjustment0min
Cooldown Time1 hr 30 min
Total Time (Sterilize + Cool)3 hr
Units per Run7qt jars

Important: Never rush cooldown — let pressure drop naturally to avoid cracked jars and siphon contamination.

Results are estimates. Actual values vary by genetics, technique, and environment.

When to Use This Calculator

Use this calculator whenever you are sterilizing grain spawn, substrate bags, agar plates, or liquid culture in a pressure cooker. It is especially important if you live at altitude, where lower atmospheric pressure means water boils at a lower temperature and sterilization takes longer. The calculator also helps with batch planning by showing how many units fit in your pressure cooker per run, so you can schedule your sterilization sessions efficiently.

Tips for Best Results

  • •Never rush cooldown. Let the pressure drop naturally to zero before opening the lid. Rapid cooling causes jars to crack and creates a sudden pressure differential that sucks unfiltered air (and contaminants) into your containers.
  • •Altitude matters significantly above 300 meters (1,000 feet). For every 300 meters of elevation, add 5 minutes to your sterilization time to compensate for the lower boiling point of water.
  • •Always load jars on a trivet or rack, never directly on the bare metal bottom of the pressure cooker. Direct contact creates hot spots that can crack jars and prevents steam from circulating underneath.
  • •Fill the pressure cooker with water to approximately halfway up the bottom row of jars. Too little water risks boiling dry (dangerous), while too much water wastes energy and extends heat-up time.
  • •Let jars cool completely inside the sealed pressure cooker before removing them. Opening the lid while jars are still hot creates a vacuum inside each jar that sucks in ambient air — along with any contaminant spores floating in your workspace.