Huge advancements in homebrewing technology have sprung a lot of interest in fermenting under pressure. I was personally intrigued by the possibilities when I first started fermenting in a pressure-capable device. Pressure fermentation is a technique in which beer is fermented under pressure, typically between 10-20 psi, instead of fermenting at atmospheric pressure (0 psi). This process has many advantages over traditional fermentation techniques, however, there are a few aspects that you should understand before you crank up the pressure on your next batch.
Benefits of Pressure Fermentation
- Reduced fermentation time: Pressure fermentation can reduce fermentation time due to higher fermentation temperatures without the production of off-flavors. This can help brewers to produce beer more quickly and can be particularly beneficial for commercial breweries.
- Fewer esters and undesirable flavors: Fermenting under pressure naturally suppresses ester production in yeast and will ultimately lead to cleaner-tasting beers, even at higher fermentation temperatures. This enables homebrewers without any temperature control to ferment at ambient temps and achieve a beer with a very clean profile and no off-flavors.
- Natural carbonation: Since the CO2 emitted from yeast during fermentation is trapped inside the fermenting vessel, it is absorbed by the solution and naturally carbonates your beverage as it ferments. This saves CO2 and eliminates the need for forced carbonation or priming sugar. The set level of pressure in the vessel will determine carbonation levels.
- Lagers at room temperature: With pressure fermentation, brewers can ferment lagers at ale temperatures with very clean profiles. This has enabled many homebrewers to successfully brew lagers much faster and without sophisticated temperature control.
- Reduced risk of contamination: Pressure fermentation can help to reduce the risk of contamination during the fermentation process, as the increased pressure can create a barrier that prevents airborne contaminants from entering the fermenter. This does not eliminate the need to sanitize your equipment!
How to Safely Ferment Under Pressure
To carry out pressure fermentation, a pressure-rated fermentation vessel is required. This could consist of a unitank or a corny keg. In order to safely ferment under pressure, you must have a means of releasing the pressure inside the vessel so it does not exceed safe levels. This can be achieved via a spunding valve. Never ferment in a totally sealed vessel without a means of pressure release or the results could be catastrophic. Do not solely rely on built-in PRVs on kegs or conicals to relieve pressure alone. It’s always best to have two forms of pressure release in case one fails or clogs.
In my trials with pressure fermentation, I’ll set my spunding valve to 10-15 PSI and let the pressure naturally build via active fermentation. The spunding valve will slowly release pressure in the vessel as it exceeds the set point. Your beer should be perfectly carbonated by the time your beer has finished fermenting.
Downsides
Certain styles of beer will not benefit from pressure fermentation. Beers that rely on fruity esters or expressive yeast character will taste muted or bland. Belgian-style beers, Hefeweizens, or New England IPAs for example all have dominant fruity esters that are critical to style. These beers should not be fermented under pressure because it will restrict the yeast’s desirable characteristics.
Dry Hopping Under Pressure
Dry hopping under pressure has been a popular strategy to lock in volatile aromas rather than blowing them out through an airlock or blowoff tube. I’ve chatted with several commercial breweries who suggested dry-hopping NEIPAs under 10-12 PSI. The rationale behind the technique is to mitigate oxygen exposure and preserve delicate hop aroma.
This is the only time I have used pressure when it comes to producing NEIPAs. Just to reiterate, this strategy only works for post-fermentation dry hopping so ester production is not suppressed during active fermentation. You can read more on Scott Janish’s trials with pressure fermentation with NEIPAs.
In conclusion, fermenting under pressure is a technique that has revolutionized the beer brewing industry. It offers several advantages over traditional fermentation, including increased efficiency, improved flavor, and reduced risk of contamination. While pressure-rated fermentation vessels can be expensive, there are several new options out there for homebrewers that are much more affordable. Depending on your situation, it could greatly improve your final product and open up some new brewing avenues.
