Pressure fermenting is a relatively new concept in the world of homebrewing. As the name suggests, it's a straight forward process that involves having your fermentation occur in a sealed vessel that is capable of holding pressure. These can be made of stainless steel, or in some cases, even specialised plastic.
There's a lot of hype around fermenting under pressure at the moment - and while the concept can seem quite daunting, it's actually very simple. The process of fermentation involves yeast consuming sugars in the wort - and the byproduct of this consumption is alcohol and carbon dioxide (CO2). In a regular fermenter, the CO2 would escape via the airlock, but in a pressure fermenter this CO2 is trapped inside the vessel which builds pressure. The pressure is regulated by a spunding valve which will control the release of CO2 from the vessel to maintain a set pressure inside.
One of the first questions many home brewers would ask is "what are the benefits of pressure fermenting?" so I thought I'd break them down in this blog post along with some of the disadvantages as well;
Advantages
Fermentation at Higher Temperatures
Fermenting under pressure allows brewers to let the fermentation occur at higher temperatures than they normally would - especially with beer styles like lagers that typically require fermentation at lower temperatures to keep a clean taste and reduce any off flavours. A higher temperature fermentation generally means a faster fermentation so this point actually has multiple benefits - the temperature can be higher, off flavours are reduced/eliminated that would normally be associated/caused by a higher fermentation temperature, and fermentation completes faster.
Reduction of Off Flavours such as Esters and Fusels
I touched on this in the previous point about being able to ferment at higher temperatures, but it's a big benefit so feel it should have it's own dedicated point. One of the most disappointing things after the hard work and patience of a fermentation is tasting your precious brew and picking up an off flavour within it. These are often caused by a lack of temperature control, although this isn't the only cause - but fermenting under pressure inhibits these flavours from developing
Reduced Krausen Size
The pressure inside the fermenter helps reduce the size of the krausen - this in turn helps reduce the risk of a krausen overflow in particularly aggressive fermentations. Be careful with this though - as when the pressure is released in the fermenter, the krausen can grow quite rapidly!
Eliminate Oxidation
This is probably one of the biggest benefits of pressure fermenting. Prior to fermentation, oxygen is an important component of your wort as it's required by the yeast in the initial/easy stages of fermentation. However, towards the end of fermentation and after it has completed, oxygen is the number one enemy of your fermented wort that has now become beer. I expect all home brewers have tasted and likely suffered from oxidised beer at some point (although they may not even know it). By completing your fermentation in a sealed vessel, with only CO2 trapped inside, the risk of oxygen being introduced to your beer is almost 0. The risk slightly increases if you need to open the vessel for any reason, such as dry hopping, but there are ways to mitigate this by using special valves/contraptions on your pressure fermenter to purge any oxygen from them prior to introducting them. You can also fill and purge your fermenter with CO2 after opening to remove any oxygen that may have been introduced from the headspace. No oxygen exposure = better tasting beer.
Pressure and Oxygen Free Transfers
Once your pressure fermentation has completed, you are now able to transfer your beer into another vessel such as a keg or bottles using pressure and silicone beer lines. This ties in with the point above about eliminating oxidation as the beer is never exposed to the air outside the fermenter, beer lines and receiving vessel. This process has been covered in a previous blog post but essentially involves using the pressure in the fermenter to "push" the beer out through a beer line.
Faster Carbonation
When your wort is fermenting under pressure, it will naturally begin to reabsorb some of the CO2 that is available in the head space of the fermenter. This is known as carbonation and is what makes beer (or any other drink) "fizzy". By re-using the CO2 that is created by the fermentation, home brewers can reduce the amount of extra CO2 they need to add from a gas bottle for this purpose and reduce the amount of time required for the beer to be carbonated and ready to consume. Compared to when fermenting at atmospheric pressure (ie. not pressure fermenting), the beer must be force carbonated in a keg by connecting a CO2 gas source from a bottle, or by adding priming sugar to bottles once the primary fermentation has completed.
Disadvantages
It's only fair we list some of the drawbacks and disadvantages of pressure fermenting as well to keep things balanced.
Not all Yeasts are Suitable
For popular and clean tasting yeasts, such as US05 or most lager yeasts, pressure fermentation is ideal and works well as it suppresses off flavours such as fusels and esters. There are however some yeasts that are not suited to fermenting under pressure. Most yeast manufacturers will now specify whether their yeasts are or are not suitable for pressure fermenting.
Additional Costs & Equipment
In order to ferment under pressure, you will need a fermenter that is capable of holding this pressure as well as some other equipment like a spunding valve, gas and liquid disconnects, beer line, keg(s) and/or a bottle filler. Thankfully there are reasonably priced options such as plastic pressure fermenters like the Fermzilla to allow brewers to dip their toes into pressure fermenting without having to outlay huge sums of money. While the cost of some of the other required equipment isn't huge either, purchasing all the little things mentioned above can add up quickly.
Leaks are Annoying
Troubleshooting leaks in your pressure fermenter can be annoying and lead to frustration if they can't be figured out - this is something I've certainly experienced when starting out with pressure fermenting but thankfully there's a lot of helpful information and guides available to help with problems like these.
Bottling
Bottling from a pressure fermenter can be difficult (but not impossible). Changes in temperature and pressure when transferring from one vessel to another can lead to excess foaming to occur and you also need a bottle filler beer gun or counter pressure bottle filler to do it effectively.
What are your experiences with pressure fermenting? Or is there something else you'd like to know about it? Let me know in the comments below
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