Under Pressure – The Ins and Outs of Pressure Fermentation

Background

Pressure fermentation, or fermenting under pressure, is one of the many techniques that have transcended the commercial/homebrew barrier. It is a technique touted for many advantages, such as the reduction of off-flavors, such as esters and fusel alcohols, increasing the speed of fermentation due to higher temperatures, and the ability to reduce the loss of volatile hop aromas.

What’s the downside? Is pressure fermentation right for me? Let’s dig into some of the ins and outs of pressure fermentation.

Pressure Fermentation in the Home Brewery

WARNING:

Using vessels under pressure presents certain risks. Before proceeding, ensure the fermenter you are using is:

1. Pressure rated for the intended use
2. Has a working pressure release valve (PRV) that will bleed off excess pressure
3. Can be fitted with a spunding valve to control the desired pressure
   • Spunding valve should be set to a pressure below what the PRV is rated.
   • NEVER depend on the PRV as the sole pressure relief mechanism

How to Pressure Ferment

Some common vessels used for pressure fermentation in the home brewery include:

• Cornelius (Corny) kegs (ball or pin lock)
• Stainless steel unitanks
• Plastic unitanks (e.g., Fermzilla All Rounder)

After brewing the wort, the cooled wort is transferred to a pressure-capable vessel, aerated, and the yeast is pitched. A spunding valve is affixed to the fermenter and set to the desired pressure (e.g., 10 psi).

There are two common methods for starting pressure fermentation:

1. Pressure is allowed to build naturally as fermentation progresses.
   • That is, there will be zero head pressure (gauge reading 0 psi) at the start of fermentation, and as the yeast starts metabolizing sugar and producing CO₂, the head pressure in the tank will increase.
2. Using CO₂, the head pressure of the tank is set to the desired pressure.

Why would you want to use pressure fermentation?

For most beer styles, pressure fermentation is not necessary, especially if the brewer is able to control the fermentation temperature sufficiently. For ales where esters are the highlight, pressure fermentation could have negative consequences, muting or eliminating the key flavor and aroma compounds you are searching for in the finished beer.

With that said, if fermentation temperature control is of concern, the use of pressure fermentation can help you produce clean tasting ales and lagers with no to minimal off-flavors. Here’s how it works.

First, increased pressure suppresses yeast growth, which in turn minimizes ester production. What that means in everyday language is that the brewer can use pressure to dial in the “clean” versus “fruity” flavors and aromas in the beer.

Second, by reducing ester formation with pressure, fermentation temperature can be increased. Increased temperature means faster fermentation! Want a lager, but don’t have or want to spend ages (okay, not ages, but weeks to months) lagering or conditioning the beer? Give pressure fermentation a go.

Which styles are Excellent candidates for pressure fermentation?

Styles that are intended to be neutral, without much yeast expression, are perfect candidates for pressure fermentation. These include:

• Lagers
• American IPA
• Blonde and Cream Ales

For styles that rely on esters from the yeast, using pressure fermentation may prevent you from making a beer that meets your intentions. For example, I once tried pressure fermenting a hefeweizen. The result: a clove BOMB. There were no discernible banana esters present and the clove-like phenolic flavors were overwhelming!

Your mileage may vary, but I would be cautious in pressure fermenting every beer style. The beauty of homebrewing is that it’s your beer to experiment with. If you like what’s in your glass, you’re doing it right.

Does Pressure Fermentation Actually Make a Difference?

Let’s start with the lager category mentioned above. The fine people at Brülosophy have performed many exBEERiments to see if drinkers could discern the difference between a lager fermented under pressure versus no added pressure. Surprisingly, and contrary to the repeated wisdom online, more often than not, drinkers were unable to pick the odd beer out of a triangle test (where 3 cups were served, with 2 cups containing the first beer, and the other cup containing the second beer) with any statistical significance.

Additionally, some ales have undergone the same treatment, including a pale ale, saison, and Belgian single.

Here’s a table of some of the exBEERiments Brülosophy has performed (with links to their posts; NOTE: statistical data taken from source articles and not verified for population requirements):

As you can see in the above table, especially when it comes to fermenting lagers under pressure, it does not seem like most drinkers can tell the difference, even with the lager fermented at the upper (or above) limit of the recommended temperature range! Only in one experiment was statistical significance reached.

Conclusions

Pressure fermentation is another tool in the brewer’s toolbox to produce beer in different ways. Have you tried pressure fermentation? What has worked for you? What have you found challenging, difficult, or not worth it with pressure fermentation?