Fermenting under pressure?

Pressure fermentation is something I have been doing for a little while now with impressive results. You may or may not have heard of this method, it is certainly not common place. While not common it has value, especially to those with limited space or resources for fermentation temperature control.

How does it work? Well a simplified description is normal fermentation but instead of using a vented fermenter that allows the excess build up of CO2 to be vented through an airlock or blowoff hose you use a sealed fermenter. Completely sealed? Nope, for safety’s sake we want to limit the pressure build up. Through research brewers have found that ideally you want to keep the pressure that occurs during fermentation to less than 14-15 psi or 1 Bar. Fermenting above those pressures reintroduces off flavors and slowed yeast production.

Why would you want to do it?

Advantages are being able to ferment at temperatures considerably warmer than you would normally ferment at without producing unwanted esters and fusel alcohol. This even allows you produce lager like beers at room temperatures. Another plus is you will end up with naturally carbonated beer at the end of fermentation. Reduced krausen which allows for less required head space in the fermenter.

One of the biggest advantages to us small space brewers is this method lessens the need for consistent temperature control. Water baths require frequent attention and a fermentation chamber requires space.

What do you need?

Well not much…

  1. A pressure capable fermenter. Please do not attempt in a glass carboy. There are a few pressure rated fermenters on the market that are rated to 15 psi, such as some new Unitanks but most are rather expensive and large for small batches. Some stainless conicals are advertised to be pressure transfer capable but that is not the same as pressure rated. A simpler solution is the standard corny keg, inexpensive and you probably already have one. Most are rated to at least 135 psi and have a built-in safety pressure relief valve. They are available in 5, 3, 2.5 and 1.75 gallon sizes. I have used the 1.75 gallon and 2.5 gallon sizes as they match my batch size, will fit in my refrigerator to cold crash or traditional lagering after fermentation as well as dispensing. This is a nice advantage to small batch brewing as you can pressure ferment at room temperature and place the keg in your refrigerator to cold crash. I have a couple corny kegs that I use for just for this and I have shortened the liquid dip tubes by about 3/4″ so after fermentation is complete you can pressure transfer off any trub or yeast sediment to another keg.
  2. An accurate and adjustable pressure relief  valve, commonly known as a spunding valve that attaches to the gas in post of the corny keg. Several online retailers sell them, below is the one I use from Williams Brewing.

spunding valve

This allows you to set and maintain the pressure you want to ferment at and keeps the existing pressure relief valve in the corny keg lid is a safety device. Adjusting the spunding valve is easiest done on an empty keg that you have charged with CO2 above the pressure you want to set it to. Charge the keg and remove the CO2 line, connect the spunding valve and adjust the relief valve to the pressure you want and it stops venting. I have had positive results at 5-8 psi as well as 12 psi. The later resulting in better carbonation of the finished beer.

If you are thinking about trying a lager you should give White Labs WLP925 High Pressure Lager Yeast a try. I have used it twice with very acceptable results. Both lagers I brewed finished in 10-12 days and were fermented at ambient room temperature of 68-70 degrees fahrenheit.

Remember to avoid pressures over 1 Bar (14.5 psi) as this can reduce yeast cell growth and can introduce increased acetaldehyde (green apple off flavor).

There is some research and testing by home brewers including side by side comparisons of beers fermenting normally and pressure fermented. So if you want to learn more or see what others’ experiences have been you can search the internet for pressure fermenting. Brulosophy did a great experiment a few years back.

If you don’t have room for a fermentation chamber or don’t want to hassle with changing frozen water bottles in a water bath you might want to consider pressure fermenting.

Recently a Pilsner was brewed using this method at temps around 77 degrees and it won a gold medal in an international beer competition. Not too shabby.

There is something new for this method and perfect for small batch brewers so stay tuned for more news!


7 thoughts on “Fermenting under pressure?

  1. For small batch brewing, what size corny keg would you use for this? Say less than 5 gal batch. Would you use a 5 gal or would a smaller keg suffice? Any issues to worry about? I’m new to this so forgive me. Thanks!

  2. Hi Kevin,
    I attended your presentation in Portland and I loved it. What you talked there was like music to my ear. I, like most of us, started out at 5 gallon batch and then migrated to 2.5 gallon in Corny kegs and love it. Everything is so much easier, nicer, lighter, faster and more fun. I was able to talk many of my friends to do the same and they love it, too.
    So being a HIMM (Hacker, Inventor, Maker & Micromaker), I put together a cool spunding valve (I call SPUNDit) to pressure ferment at 5 psi and 15 psi after dry-hopping AND I could capture CO2 to purge another keg during active fermentation for closed-transferring of clear well-carbed beer after cold-crashing. Oh! it’s clear because I made a floating draw tube that only draws beer 1/2″ from the surface and 1/2″ from the sediment/yeast. And what also really cool is, after transferred all the beer out of the fermenting keg, I added 1.5 gallon of apple juice + 0.5 gallon grapefruit juice from my backyard, set the SPUNDit at 15 psi and fermenting for 3 days, cold-crash for 2 days and have delicious/delightful hard cider with hints of grapefruit/IPA/hops.
    Another cool thing is, while the cider is fermenting at 15psi, I capture its CO2 to draft the serving beer keg at 8-10 psi. So I basically use it as a personal CO2 generator.
    I made a few extra SPUNDits and put them on eBay for fun. I sold over 40 in 2 months and most of them to overseas even with expensive international shipping. You can check it out there.
    I thought I like to share all this with you.
    Best regards,

    • Trong,
      Thanks for the kind words and checking out my blog. I think pressure fermentation has a place in home brewing but still not discussed much but I believe it can provide great possibilities to those without adequate temperature control. Finding a spunding valve that is accurate has been difficult but if yours has the ability to reclaim some CO2 that is great. I’ll have to give yours a try.

  3. I have tried Trong’s SPUNDit to much enjoyment and satisfaction. The quality craftsmanship is second to none; these are built with extreme detail and passion. Worth every penny. I recommend this highly.

    Don S. Everett WA -GEBL

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