Performing Closed Transfers

Brewing has a long and beautiful history and the techniques we use have evolved tremendously, especially on the homebrew-scale, over the past decade. We’ve seen new tools and brewing setups hit the market more often and it’s not uncommon to chat with homebrewers with setups that are practically mini versions of commercial breweries, allowing homebrewers access to nearly every technique and tool the pros have. 

One of the most significant gear upgrades a homebrewer can make is to add the capability of doing closed transfers from the fermenter to the keg, virtually eliminating oxygen exposure that could potentially lead to oxidation of the beer. Oxidation is likely the biggest issue that plagues homebrewers, causing the “homebrew flavor” reputation I’ve heard a few times too many. Even small amounts of oxygen can cause a delicious batch of beer to take on chalky, wet cardboard, and caramel notes that oxidation can cause. 

Typical efforts of reducing oxygen exposure include transferring finished beer as gently as possible into the keg or bottles, purging bottles and/or kegs with CO2 before filling, and capping bottles on foam. But the closed transfer is the one technique that will ensure the cleanest transfer possible. 

Let’s put the auto-siphon in a timeout so we can explore the gear needed and the process of successfully kegging your brews with a closed transfer.  

Required Gear 

The fermenter is the first piece to this puzzle. The key requirement for a successful closed transfer is the ability to move fermented beer from the fermenter into the keg without exposing it to oxygen by using the proper connections and tubing. These days, many stainless or PET fermenters are pressure-rated and capable of handling direct CO2 transfer. There are many options available, and the price range spans from about $100 for PET fermenters like the FermZilla to well over $1,000 for the stainless unitanks from companies like Blichmann Engineering, Spike Brewing, or Ss Brewtech. It’s the brewer’s choice what options and features they want available to them. For yours truly, the biggest challenge was convincing my wife to let me spring for the stainless gear. The capability to do closed transfers and have precise temperature control gives me the ultimate cold-side brewing control; and you can achieve those with most pressure-rated gear out there. 

An honorable mention also needs to go out to glass fermenters that have special rubber toppers that allow for a racking arm and CO2 connections. Extra caution needs to be taken when dealing with glass in general, but please be mindful that too much pressure could make that glass carboy a particularly dangerous accident-causer. PET and stainless fermenters are preferable. 

The next tool we need is an external CO2 source. Typically, this is a CO2 tank with an adjustable regulator that allows us to feed CO2 into the fermenter via the gas post. Most pressure-rated fermenting setups are equipped with a gas post that doubles as the connection for the blowoff tube and as the input for CO2 for when fermentation is complete. 

Transfer tubing and the connections can vary from setup-to-setup, but the important part is that the correct connections are present to go from the output of the fermenter to the liquid line of the keg. Most homebrew setups these days are ball-lock, but the connection could also be pin- lock, tri-clamp, or Sanke — outfit your system accordingly. 

I’m always amazed by the ingenious solutions homebrewers come up with, so I’m sure there are other ways of setting up a closed transfer, but the pressure-capable fermenter, a keg, and transfer tubing are the required gear. There are a few tools that can make this process easier and more efficient, so let’s next talk about those for a minute. 

Optional Gear

Filters: In-line filters can assist in catching trub or hop matter that we don’t want in the serving keg. There are many options for these, and they all do about the same thing. Features I consider when picking a filter are reusability (I don’t want to have to buy new filter cartridges all the time), cleanability, and simplicity. In the picture on page 51 you’ll see me using the BouncerMD inline beer filter. Bonus tip: You can use these types of filters to infuse beers with flavoring if you want. I’ve done this in the past to infuse beer with coffee and orange peel during transfers. 

An inline filter is useful to catch trub and hop matter as beer flows from fermenter to keg.

CO2 capture device: CO2 can be expensive or hard to come by in certain places, so letting it all vent out into the atmosphere after purging or displacing the beer in the fermenter is a shame. I’ve seen folks capture the CO2 that was in the receiving keg by connecting the blowoff to the gas post of another keg that is full of sanitizer and adding a blowoff to the gas post of the keg, essentially repurposing the CO2 for a second keg purge. Bonus tip #2: That same setup can be used to purge a keg using the CO2 generated during fermentation. I’ve pushed sanitizer though three daisy chained kegs using “recycled” CO2 generated during a fermentation. In my case, it just takes the ball-lock connectors going from the blowoff of the fermenter to the gas post of the keg, and then another blowoff out of the receiving keg.

Spunding valve: Attached to the keg, a spunding valve can prevent oxygen from entering the keg because it is a one-way valve that can be adjusted to be fully open (trapping no pressure) while also giving the brewer the ability to control the CO2 pressure in the keg during the transfer. This is critical when transferring carbonated beer. More on that in a moment. 

Brewery scale: This is a useful tool for those who have steel gear. By watching the weight of the beer increase in the receiving keg you can predict when the transfer is complete, know that the transfer isn’t stuck, and pause the transfer when the desired fill level is achieved. For example, a 10-gallon (38-L) batch being transferred into two separate Corny kegs would need to be paused when the first one has reached its fill.  

Let’s Get to It!

Setup for a closed transfer is simple. The absolute first thing, though, is to thoroughly sanitize everything and prepare the keg to receive the beer. In my process, I sanitize and purge kegs right after cleaning them by filling them with sanitizer solution (1 oz./30 mL of Star San in 5 gallons/19 L of cold water) and pushing the sanitizer out by connecting CO2 to the gas post and a liquid-out line to the liquid post. I do set this up as a daisy chain with multiple kegs when I do this so I’m not losing all that CO2 and sanitizer for just one keg. Once the liquid is pushed out, I remove the liquid line-out and allow the CO2 to build up a little pressure. This ensures that there is no oxygen in the keg, everything is sanitized, and I know that the keg is sealing and holding pressure properly. If using a glass carboy or a fermenter containing no residual pressure (from carbonating in the fermenter or applying positive pressure with CO2) then the receiving keg needs to be purged of any pressure before it gets connected to the transfer line. Otherwise it will push CO2 back into the fermenter, which will either stir up trub or possibly damage the glass carboy if it can’t handle applied pressure. That is not a mess that I wish on anyone since it took me literally four hours to clean the mess up after I exploded a glass carboy full of beer a few years ago. Lesson learned: Purge the pressure unless you’re transferring carbonated beer (we’re getting to that).

Next, I take a bucket of sanitizer and put the transfer tubing in, filling the line and then trapping that sanitizer in the line with the ball-lock disconnects. This ensures that the line is sanitized, and it will prevent the air in the hose from pushing into the receiving keg. I purge the sanitizer out of the line right before connecting it to the keg, don’t worry. 

I disassemble the filter and put it back together while submerged in sanitizer and make the connection between the filter and the transfer line. Some call this “packing the line” with sanitizer. The next step is to connect the transfer line to the fermenter. The photos throughout this story show my gear, including the Spike Brewing FLEX+ fermenters equipped with tri-clamp connections, which have a racking arm inside that allows the brewer to pull from beer that is above the trub layer. Other options include bottom dump fermenters, or systems that come with a floating dip tube that transfers beer from the top — in any case, make the proper connection for your setup. 

To begin the transfer, connect the CO2 to the fermenter and apply the proper psi. This could range from 1 or 2 psi for low pressure-rated systems, or 10–12 psi for sturdier steel setups. The pressure of the receiving keg is important too. When transferring carbonated beer, the pressure of the keg needs to be close to the pressure used for pushing the beer; only a few pressure points lower. The pressure differential determines the direction of the flow and the size of the difference determines the flow rate. For example, if I’m pushing carbonated beer into a keg, I’ll set the regulator on the fermenter to 12 psi and the spunding valve on the keg to 10 psi. This allows a gentle transfer that will keep foaming at bay. If you’re transferring flat beer into the keg then this is less important; you can just pull the pressure relief valve (PRV) at the top of the keg to allow the CO2 out while the liquid flows in. Some may opt to use a blow-off tube into sanitizer to completely prevent oxygen ingress, but as long as there’s positive pressure entering the keg that is unlikely to happen. 

Carbon dioxide is connected to one port on the fermenter to push beer out the other port and into a keg at a low PSI to conduct a closed transfer.

Once CO2 pressure is applied to the fermenter it’s time to clear the sanitizer out of the line and then connect it to the keg. I simply open the butterfly valve on the fermenter and then depress the ball-lock at the end of my line with a sanitized finger. Once clear beer is flowing, I connect that sanitized ball-lock to the sanitized liquid post line on the Corny keg — we’re now transferring! Once a little pressure is built up inside the keg, I’ll either lock the PRV on the keg in the open position or dial in the spunding valve to bleed pressure at the desired number. The brewery scale is handy at this point too because I can watch as the weight increases. As a reminder: Five gallons (19 L) is approximately 41.5 lbs. (18.8 kg), but can vary slightly depending on the beer style. 

As the transfer nears completion, I prepare to close the PRV on the keg and the butterfly valve on the fermenter. We want to prevent oxygen ingress and prevent excess CO2 from agitating the newly kegged beer unnecessarily. Once those are closed, I connect the CO2 to the keg and pressurize it to serving/carbonating pressure of about 13 psi before purging it a couple times just to be sure that any oxygen that somehow entered the keg gets pushed out. I then put the keg in the chiller and let it carbonate, if it isn’t already, before putting it on tap and enjoying the new beer!

Clean the fermenter and gear and you’re good to go. We’ve now completed the closed transfer and given our beer the best chance of not getting oxidized during packaging, ensuring lasting flavor, color, and longer shelf stability! 

Issue: May-June 2023