What is “fermenting under pressure”?

Fermenting under pressure is the process of fermentation to happen in a closed vessel. Instead of allowing CO2 to release through a blow off tube or airlock, fermentation occurs in the vessel and gains pressure over time.


What are the risks of “fermenting under pressure?”

When fermenting under pressure, CO2 is being built up inside the vessel as fermentation speeds up. If an exit port (Pressure Relief Valve and/or Spunding Valve) becomes clogged and air cannot escape, if high enough pressure is reached, the fermenter lid can explode off potentially injuring or killing someone.


How do I ferment under pressure safely?

  • We designed our 3-port lids for our fermenters to make sure brewers are fermenting safely.
  • If using our 3 port lid, we recommend using a our All-In-One PRV to safely pressure ferment or spund.  (Note that our gas manifold is not suitable for pressure fermenting or spunding)
  • Do not use spunding valves that do not have a 1.5" TC connection. There are many small port Spunding Valves on the market that simply don’t have a large enough exit hole. The Blichmann ‘spunding valve’ and common ‘bowtie spunding valve’ are examples of ones we would not recommend. These can become clogged during fermentation and reduce the opportunity for CO2 to escape if needed. We only recommend a 1.5” full port tri-clamp Spunding Valve.
  • Do not place a valve between the fermenter and your Spunding Valve or Pressure Relief Valve. If you forget to open this valve, you’ve rendered your air release points as useless.
  • Never exceed the operating pressure of the tank which is 15 psi.