Pressure Fermentation
Pressure fermentation has been growing in popularity within the homebrewing community in recent years. The benefits are tangible and numerous, and the equipment required to ferment under pressure are now more widely available and affordable for the average homebrewer.
First, let’s discuss what exactly pressure fermentation is. In short, it’s simply the process of fermenting at a pressure greater than atmospheric pressure (0 PSI). The pressure is created by forcing CO2 into a pressure-capable vessel at the beginning of fermentation and holding that pressure for the duration of the fermentation process and/or letting the CO2 pressure build naturally as fermentation progresses.
The pressure inside the tank allows fermentation to take place at a quicker pace and at a higher temperature (up to 10 degrees higher) compared to traditional methods at ambient pressure. Despite this higher temperature, ester production in yeast is suppressed, locking in the same crisp and clean taste normally achieved through non-pressurized fermentation, especially for lagers. Beer styles which rely on fruity esters to define their style, however, may not fully benefit from pressure fermentation. The exact pressure levels used to pressure ferment will also depend on the beer style and yeast being used, but typically ranges from 10-15 PSI.
Pressure fermentation also allows carbonation to occur naturally by capturing exerted CO2 and absorbing it into solution towards the end of fermentation. This same CO2 containment process (vs standard CO2 blow off during traditional fermentation) also helps to preserve hop flavor and aroma in hoppy beer styles, in addition to reducing the additional step and materials needed for forced carbonation or bottle priming.
Special equipment is also necessary to safely ferment under pressure. First, a pressure-capable vessel, such as a unitank, is required, with an operating pressure of at least 15 PSI. Unitanks should have a reliable tri-clamp sealing system to guarantee pressure remains within the tank throughout the fermentation process.
Secondly, a spunding valve (pictured here), which is simply an adjustable pressure release valve, is required to help manage pressure levels during the fermentation process. This works by dialing in the desired PSI level on the spunding valve, which in turn automatically vents off excess pressure once pressure increases beyond the preset level. This system warrants that pressure is maintained at a specific and consistent level throughout the fermentation process. The spunding valve is also a critical safety component, so it’s a must-have when pressure fermenting, and should ideally be used in addition to the tank’s standard pressure release valve (PRVs sometime clog due to krausen buildup so having redundancy is the best way to minimize safety risk in case one were to fail).
Finally, a pressure gauge should be included either directly attached to the spunding valve assembly or independently fitted elsewhere on the tank. The pressure gauge is needed to help set and monitor tank pressure throughout the fermentation and carbonation process and is useful to help calibrate and validate proper functioning of the spunding valve and other PRVs in the system.
In summary, pressure fermentation, which was typically limited to commercial brewers, is an exciting new technique now available to homebrewers. It offers the ability to simplify and accelerate the fermentation and carbonation process while boosting hop flavor and aroma, all in a single vessel!