Sunday 10 October 2021

Quick & Easy Guide to Pressure Fermenting

In a previous blog post I covered some of the benefits of pressure fermenting. In this post I'll cover the process for actually performing a pressure fermentation and some frequently asked questions (FAQs)

What do I need to perform a pressure fermentation?

  • A fermenter capable of holding pressure - some popular options are Kegland's FermZilla and Keg-King's Apollo or Fermenter King/Junior
  • A spunding valve (to control/regulate the pressure within the fermenter)

How do I do it?

Fill your fermenter with your wort and pitch your yeast as you normally would. Put the lid on and seal the fermenter

Do I need to apply CO2 gas pressure prior to fermentation starting?

This is a common question amongst new starters to pressure fermentation. My answer to this is "no", you don't need to apply CO2 gas to the fermenter prior to fermentation starting. You can if you want to, but it isn't necessary.

Yes, there is oxygen present in the fermenter at this point, however, once fermentation starts, the yeast will begin producing CO2 that will expel all the oxygen out of the fermenter via the spunding valve.

I've never applied gas to pressurise the fermenter prior to any of my pressure fermentations and have never had any ill effects.

What PSI should I ferment at under pressure?

Another common question - and there's a few things to consider for your answer. A good starting point is 10-12 psi of pressure. Some people use more than this, which will lead to a more carbonated beer at the end of fermentation, but will potentially stress the yeast more. Pressure does help to reduce unwanted off flavours and esters which may or may not be desirable depending on what sort of beer you're making.

Another consideration is if you need to open your fermenter after fermentation has begin for dry hopping. If there's a large amount of pressure in the fermenter, releasing the pressure will often lead to the krausen expanding - rapidly - which is exacerbated if there's a large amount of pressure to release. The method I use is to start off fermenting at a low pressure (5psi or less) so there is less gas pressure to release to open the fermenter for dry hopping. Once this has been done the pressure can be increased to 10-12 psi.

Do I need to use a spunding valve? Isn't that what the PRV (pressure release valve) is for?

A spunding valve in addition to a PRV is always a good idea. It's all about safety and points of failure. If you solely rely on a PRV to maintain the pressure in the fermenter then you have a single point of failure. If there is a problem with the PRV (such as from a blockage from an aggressively high krausen) - the PRV may not function and pressure could easily exceed what the fermenter is rated for. If you have a spunding valve AND a PRV, then you have two points of failure. The spunding valve will cover the main duties of maintaining the pressure, and if a problem occurs with it for some reason, you've then got the safety net of the PRV. Always use a spunding valve.

What yeasts are good or suitable for pressure fermenting?

Yeasts that typically produce neutral flavours and characteristics are good candidates for pressure fermenting. Some examples are SafAle US-05 and Lalbrew BRY-97 and most lager yeasts due to the clean tasting nature of them.

Does pressure fermentation take longer?

No. If anything, pressure fermentations should be completed faster. This is because you are able to ferment at higher temperatures when fermenting under pressure.

What temperature should I pressure ferment at?

Another common question that has no real right or wrong answer. Personally I stick to the recommended temperature range for the sort of yeast that I'm using. You can go higher as pressure fermentations suppress the off-flavours that are generally expected when fermenting at the higher end, or even above the recommended yeast temperature range. But just because you can, doesn't mean that you should. If you have the ability to control the fermentation temperature then you should.

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