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​The Ins and Outs of Pressure Brewing

​The Ins and Outs of Pressure Brewing

Following on from Greig’s previous pressure fermenting article, we thought we would give you a guide to getting started and some pointers. The information in this article may be helpful to both new and experienced homebrewers alike. Brewshop stock a number of pressure capable fermenters which have become very popular:

FermZilla Allrounder
Ss Unitank

Why pressure brew?

Being able to ferment, condition, carbonate and serve from the same vessel is a massive incentive for brewing in a pressure vessel. Cutting down or virtually eliminating any contact with oxygen, which is one of the culprits of bad homebrew, is also a big plus. Having the yeast naturally carbonate the beer for no cost saves your precious CO2 bottle and if you are kegging, it is quite handy to transfer your beer to a CO2 purged keg without too much fuss.

Pressure vs Yeast

Before we delve into the details of pressure fermenting, let's take a minute to talk about the real stars of the show behind your delicious brew, the yeast. Often neglected in bad home brew, healthy and happy yeast make good beer. Putting too much pressure onto these guys will cause the yeast to freak out and cause off flavours from yeast stress. Pressure fermenting does have the effect of muting any yeast characteristics, which can lead to cleaner beers but too much pressure can cause the yeast to die or drop out prematurely, leaving compounds such as diacetyl behind (which tastes bad). In some cases, it will be beneficial not to brew under pressure at all (more on that below).


Now that we know we need to look after the yeast, let's get onto the equipment we need. Pressure brewing is going to make more sense if you have even a basic kegging setup including a CO2 bottle, and the understanding behind it. It's also important that we use a spunding valve in conjunction with the fermenter. This limits the pressure the fermenter can get too, so as not to cause too much stress for the yeast. The spunding valve connects to the “Gas Post” on the fermenter. Setting a spunding valve to anywhere from 0-15 PSI for primary fermentation won’t stress the yeast too much, with most brewers choosing 10-15PSI. It's worthy to add that spunding valves or PRV’s (pressure relief valves) will also save your vessel from potentially exploding, which can cause a big mess or potentially dangerous consequences. Safety is always paramount - even stainless fermenters will explode or implode if used carelessly. If you are thinking of buying an Ss unitank, a PRV comes built in and is set to about 18 psi. If you are using a FermZilla or Kegmenter, the built in PRV is not a spunding valve, but a safety mechanism. These are the most popular Spunding valves:

Spunding Valve - Kegland types

Ss Spunding valve

Set your spunding valve using a keg. If aiming for 12 PSI, set your CO2 regulator to about 15 PSI, and fill your keg to that level. Give the yellow dial on your spunding valve a few turns clockwise and attach it to the keg, then bring the pressure down by turning the blowtie anticlockwise until the gauge is at the desired level. If you don’t set your spunding valve, you will need to monitor the first day of fermentation closely. It would be best to wind the spunding valve fully out/ anticlockwise and wait for active fermentation and slowly wind the blowtie in until you are sitting at the desired level.

Pressure Kit

If using the FermZilla range, you need to get a plastic or stainless pressure kit (Kegmenters include these as standard). This lets you connect ball lock fittings such as your spunding valve, CO2 bottle, beer transfer lines or a beer tap. The pressure kit makes the FermZilla basically work the same way as a cornelius keg, with a floating dip tube. Generally, you will attach your floating diptube to one side (liquid out), using the underside of the cap. On the other side is your gas post for your spunding valve and gas in later on. You can write on the caps or now get an alternative colour so you can easily distinguish which side is which. If you have a kegmenter, the fittings are the same as a corny keg.

While stainless is desirable in brewing, for sanitisation we found the plastic caps are fine and actually seal easier on the FermZilla lids.

All Rounder set up in fridge with temp control and spunding valve.

Kegmenter with spunding valve attached to the gas post.

Set up your spunding valve on one of the posts; again, it does pay to mark it clearly as a “gas” post or you can purchase a different colour so you don’t mix them up as you definitely do not want beer through your spunding valve! The Fermzilla pressure caps will accept both gas and liquid connectors. Attach the floating dip tube to the other “liquid” post for sampling and kegging.

Brew Day

You’ve done the hard yards and either spent several hours mashing, sparging and boiling or you have some extract ready to go, and your pressure fermenter is sparkly clean and sanitised. Time to fill it up, but not so fast! Let's pressure test our vessel to make sure it is sealing correctly to save issues down the line.

Fill your fermenter with a few litres of your favourite sanitiser, seal the lid, make sure everything is sealed and tight (hand tight is best), and give it a good shake up. Using your CO2 bottle, fill to a nice round number, let's say 12 PSI. Attach your spunding valve to the “gas” post and try to set it so it stays around 10-12 PSI. Observe the PSI level over a period of 5 - 10 mins and make sure it remains static - while your wort is chilling is a great time for this. Also, using a Star San spray bottle, spray around the lid and seals for any leaks.Using a picnic tap on the liquid post, pour some sanitiser out, and this will sanitise the inside of the silicon liquid line and post.

It is the same principle with Ss unitanks except the PRV is already preset at about 15 PSI. When it is all sealed, release the CO2 and empty out the sanitiser.

Time to fill the fermenter, oxygenate the wort and pitch the yeast. Once filled up, seal the lid and attach the spunding valve. Continue to monitor the pressure level as it rises up to the set level.

One of the benefits of pressure brewing is sampling your brew. This makes taking gravity readings easy - just make sure you are sanitising everything throughout. Carry out the fermentation schedule of your beer, dry hop if needed (more on this below) and after a decent diacetyl rest, it's time to cool things down. At this point, we should have a good amount of CO2 in our beer (for free!) but it will not be quite enough. As we cold crash the brew, CO2 will be absorbed into the beer. You will need to top up the fermenter with excess CO2 from your bottle to risk the fermenter going into negative pressure, or worse, imploding. This is a major drawcard of a pressure fermenter: you can serve and drink right from the tank! But let's not get carried away - let's send the beer to its natural environment, the keg.

FermZillas and Ss unitanks have the capability to perform a yeast dump, meaning you could chill and condition in the same vessel.


The first thing we need here is our transfer line. This consists of two beer connectors (black for consistency) and some beer line. You could add a small filter housing if you are concerned about hop matter, but most of the hops and trub in your fermenter will be pushed to the bottom. Let's clean and sanitise our keg, and also sanitise our transfer line. To do this leave a bit of sanitiser in your keg and put some pressure into the keg from your CO2 bottle. Connect one end of the transfer line to the liquid post on the keg, and either send the sanitiser to another keg, or simply connect the other end to a spare carbonation cap and drain the sanitiser out. This will also purge the keg.

Now that the keg and transfer line is clean and purged. let's fill the keg. It pays to drain the first small amount of beer from the fermenter out as it may contain a small amount of yeast or hops. Sanitise caps and posts, remove spunding valve from your fermenter and attach it to the gas post on your keg, and attach your CO2 bottle to the gas post on your fermenter. Finally attach the transfer line, liquid out to liquid in on the keg. The spunding valve should be set to around 12-15PSI from fermentation. You'll need to set your CO2 regulator on your bottle slightly higher to get a decent flow, but after a few times you'll get the knack and the levels that you are comfortable with. Last word of advice, don't over fill the keg as beer will come out the spunding valve - it sometimes pays to remove it towards the end! Keep an eye on the level using the scale on the fermenter or weigh the keg.

This is the process most breweries will use. There is, however, another way where you direct the gas from the keg back to the fermenter using a “loop”. This works well and saves a bit of CO2, but using the above method ensures no pressure loss, and no yeast and trub rising up from the bottom of the fermenter during transfer.

Keg transfer from a FermZilla

My opinions on when to use pressure fermenting and when not too.

Both myself and most of the Brewshop team have quite a few pressure brews under our belts. Here are some of my experiences of when and how to use pressure fermentation.

Hoppy beers and dry hopping

This is often a hot topic for new brewers and has mustered a whole field of techniques, debate and problem solving. An early common opinion was that pressure fermenting kept all the lovely hop aromas in the brew, saving them from being blown off. Although this could be true, I personally find not much difference in hop aroma in pressurised and non-pressurised fermentations, in primary fermentation anyway. The issue for most comes when it comes to dry hop in a vessel that is under pressure. There are all sorts of devices that have surfaced such as the Dry hop device for FermZilla, and many tri-clamp fittings for unitank (see pic below). The idea is that you open the ball valve and your hops drop into the beer. It takes a bit of practice (and pressure) to get this to work properly. Personally, I find nothing wrong with opening the lid and dropping the hops in. You will need to drop the pressure in the fermenter over time (an hour or so) so that all the beer will not rush out, but then open the lid and quickly add the hops and shut it up again. Some people may be scared of oxygen exposure but the reality is you have CO2 escaping from the vessel and you still have a bit of fermentation left to clean things up, so it will be fine.

Moving on from this, let's not forget that we don’t have to pressure brew every time. In fact, most of the best commercial IPAs you have tasted were probably not pressure brewed at all. I find some ale yeast strains do struggle and stress under pressure a bit, but others are fine. If you purchase a Fermzilla, it comes with a cap to use with an airlock or you can use a ball lock connect and some gas line to a blow off into a jar of sanitiser (see pic below). If you use a stainless unitank, you can simply open or close the valve on the blow-off cane. I have had success with hoppy beers by not brewing under pressure until the dry hop and D-rest. This is when we can close the fermenter up and get some of that free CO2! Wait for the beer to be within 10 points of finishing up, close it up (add a sanitised carb cap where the airlock was on a FermZilla). Attach a spunding valve and wait a bit to create a bit of CO2 pressure in the headspace. Release the pressure, add the dry hop and seal the fermenter up again. This method is common in commercial breweries as well.

Lagers and other ales

Lagers are one of the few beers that will benefit hugely from brewing under pressure. Actually, it is quite easy to get a clean and tasty lager without too much fuss, and there is no need for dry hopping either. The pressure mutes most of the characteristics of the yeast meaning you can easily ferment at 18 degrees or even higher. It also means instead of 8-12 weeks, you can get a decent lager out in less than half of that. These lagers will lack some of the characteristics of true lagers though. When it comes to other ales, I just want to point out right away, do not brew Belgian beers under pressure. You want the happiest and healthiest yeast possible in these beers and sometimes they are intentionally underpitched, so don’t do it. Apart from Belgians, some ale strains will handle pressure with no issues, some won’t. In my experience a lot of British strains are great under pressure, retaining fruity esters. Kviek strains seem great as well but some character strains like Kolsch yeast can struggle. Time to start trying some strains out for yourself and collecting notes. Also please share your findings on our Facebook group.

Ss Unitank set up with spunding valve and Dry hopping device/hopper.

FermZilla AllRounder with a non pressurised fermentation.

A final note

To wrap things up, we have looked at the process of pressure brewing and also a few tips and tricks. I would like to end with a final note of advice. Pressure brewing is not superior to traditional brewing methods and will not produce a superior beer, but if done right it will make great beer. Although fermentations can be a lot quicker, beer still requires aging and conditioning, so don't skip this. Also, pressure brewing is definitely not a quick fix for poor brewing practices, but as we have seen it does have its place and makes things a lot easier, oxygen free and cleaner, especially for us homebrewers. Good luck!