Forced carbonation – Ep.2: Testing

In the previous episode we left with the the theory and the planning of the transition to kegs and CO2. Now it’s time to tell you how the experimentation went.

WARNING: Working under pressure can be very dangerous, especially if you do not use the correct equipment. This is a test for a future inox system made with plastic equipment that absolutely should not be brought under pressure. If you want to follow this path I recommend you to directly use stainless steel kegs or specific fermenters.


First I started looking for some kegs on the various markets on Facebook. In a short time I found from a guy from Naples two completely regenerated 19 liters Cornelius kegs at 35€ each, sanitized and with the gaskets replaced. Maybe not the best price, but considering that the kegs were as new that was not a problem for me.

A few days later I went to nearby Slovenia to Figelj, partner of the Homebrewers Gorizia association, to buy a CO2 tank. I found quickly a 10kg tank for about 180€ as well as a discount as a partner of our association.

I found the Beergun on Aliexpress for 33€, and in less than three weeks it had already been delivered to me. I was finally able to measure the diameters of the tubes that actually matched with the online documentation.

I’ve been thinking about the pressure gauge for the keg. If this system will work, I want to try to ferment under pressure, this is why I decided to buy directly a spunding valve in order to use it in both situations.

Everything else, that means John Guest fittings, Jolly connectors and pressure reducer, instead I ordered directly from the Mr. Malt webshop together with the ingredients needed to make two test beers with which I would have verified the whole process.

The only thing I didn’t buy was the 9.5mm pipe: for some reason my friend Giovanni had a whole package at home, so he kindly gave me several meters.


I started with the easy part: check if the hose fits to the Beergun: the hose adhered well to the gas holder while the beer hose fit perfectly into the John Guest connector.

At this point I moved to the fermenter. First I drilled two holes of 21 mm on the lid of the fermenter. I have inserted the two bulkhead connectors together with a gasket on each side for each of them. Then I cut the John Guest cap to create a rigid pipe on which to fix the silicone tube of the floating sphere. Then I shortened the silicone tube to match the height of the fermenter and tried to stick it on the cutted pipe. I admit that despite the softness of the tube it took a while, but in the end adhered to perfection and even pulling did not take off.

All that remained was to perform a test: I mounted the John Guest regulator and adapter on the CO2 tank (for which my dad built a cart in the meantime), filled the water fermenter and tried to push that water into a bucket. Everything worked as planned, it seemed almost too easy.

Phase 1: Fermentation

Since it was grapes harvest time I decided to make my traditional IGA as a pilot for this system. Nothing to do with the project, but I decided to increase the amount of must to understand how it affected the taste of the final beer.

While the beer was boiling I provided to pierce the wall of the fridge where I would ferment the beer to pass a piece of 9.5mm hose: I had to use this hose for the cold crash, but I didn’t want to drill holes and work with the screwdriver with the fermenter in the fridge. At the end of brewing I filled the fermenter and closed the lid with the ball floating on the wort. I mounted both taps and brought the CO2 exhaust pipe into a jar full of sanitizer, letting the yeast work in peace for about 14 days.

At this point it was time for the cold crash. First I closed the gas tap on the fermenter and pulled off the hose. Then I connected the hose that came out through the fridge wall to the CO2 tank and adjusted the flow so that the gas outlet was slightly perceptible. By letting it blow I put the hose on the gas tap of the fermenter to avois the presence of oxygen in the hose. I opened the fermenter gas tap and “nothing happened”, which means the system was working as planned. I directly set the target temperature and left it all to rest.

The next day I did a check, the temperature was now at the target point and everything was in order: for the moment a success! I closed the fridge and left everything untouched for about three days.

Phase 2: Keg transfer

First I took one of the two kegs, opened and sanitized it: despite it was already sanitized I wanted to try the whole procedure. So I first made the sanitizer flow from the beer connector trough the inner pipe into the keg. After that I closed the keg and with several shakings I sanitized it. After I drained it, I had to eliminate the oxygen in it. Based on what books says and from what was discussed with other homebrewers, I decided to do a series of CO2 in/out cycles (four or five will be enough). In this way at each discharge I would remove part of oxygen from the keg.

At this point I connected everything to the closed taps, adjusted the tank pressure to the minimum necessary and discharged the CO2 from the keg. Theoretically, by opening the tap to the keg and the tap from the CO2 tank, the beer would have to drain into the keg. Well I made a mistake: I forgot to open the tap that from the final keg went into the CO2 blow off jar before opening the one that from the fermenter brings to the keg. The minimal remaining pressure in the keg (too much for a simple plastic fermenter) moved backwards into the fermenter. To avoid that the fermenter brokes up, I disconnected a hose to discharge teh exceeding CO2 and everything returned to normal. However, I decided to suspend the test and let the beer rest in the cold in case the sediments moved.

Two days later I tried again, this time opening the taps in the right order. As expected the beer began to move in the keg and the numbers on the scale began to move upwards.

Once the keg was filled, there was still some beer left in the fermenter so I decided to pour it directly into 75cl bottles to make them refermentate in the old way. In this way I could also make a comparison of the two techniques.

Phase 3: Forced carbonation

You could say that for the worst was over. The part that most worried me was going from plastic equipment to equipment that supports pressure, and despite the mistake it worked as expected.

Once closed the tank and the pressure regulator, I connected it through the hose that enters the refrigerator to the beer connector of the keg, while on the gas connector I mounted the spunding valve completely closed. After consulting the carbonation table I opened the tank and started to slowly raise the pressure until It reached the desired value, considering that I would have carbonate, as recommended, at 7 ºC.

Every time I raised the pressure there was a sound of bubbles in the keg and the pointer of the spunding valve began to rise. Since the movement was not instantaneous, I waited a while before rising again to give the pressure gauge time to adjust to the exact pressure. I have to confirm what has been said to me: the reading of the gauge placed on the keg is definitely faster and more precise than that on the tank, even if probably it is only a matter of giving time to the various manometers to stabilize.

The book explained that there is no exact timing when beer would absorb the CO2, and the speed of this process varies by temperature. Since I wasn’t in any particular hurry I decided to leave the beer to carbonate with the tank open for two weeks. After two weeks I tried to pour a beer directly from the keg and it was perfectly carbonated. All that remained was to bottle it.

Phase 4: Bottling

At this point it was time to try the beergun. After sanitizing hoses and beergun, I connected through a John Guest splitter a hose to the gas connector of the keg and the other to the beergun. A third hose connected the beer line of the keg to the beergun together with a safety tap.

I put the beergun in the bottle ’til the bottom and pulled the trigger: opposite to what I expected the bottle filled with foam. After a few bottles, however, it stopped foaming allowing me to fill the bottles well. I came to the conclusion that simply the post-carbonation pressure of the keg was excessive, and probably discharging some gas from the keg before starting would avoid foaming in the first bottles.

To avoid oxygen in the bottle I followed the advice of the book by extracting the gun as the bottle fills. Once you reach the neck a shot of beergun will create a bit of foam to fill it, an action that requires a bit of practice. In a short time I emptied the keg without any particular hitches.

Phase 5: Tasting

I took advantage of the Christmas holidays to open at the same time two bottles, one refermented and one forced, to make a comparison:

  • Appearance: keeping the sediments in the refermented bottle, the two beers appeared similar, with a more persistent foam in the case of the refermented beer;
  • Aroma: The refermented had initially hints of yeast that almost covered the aroma of wine but that with time disappeared. Together with these scents, however, the main aroma was slightly softened. The forced one instead immediately presented the main aroma keeping it intense and pleasant over time without any off-flavor of yeast
  • Mouthfeel: The sensation in the mouth revealed an error in the bottling phase: I did not consider the loss of carbonation in the transition from keg to bottle with no pressure. The carbonation was much more decisive and adequate in the refermented beer. Therefore, to bottle a slight over-carbonation is required.
  • Taste: The taste of the two beers was quite similar, although in the refermented one it was more sharp and a little less pleasant as well as leaving a slightly more intense and annoying alcoholic sensation

Despite the error of carbonation the quality of the product, the aroma and taste were much better in the forced version. My friends also enjoyed this beer much more, telling that it was cleaner and tastier.


I am extremely satisfied with the results of this test. Apart from some problems caused by simple inexperience the process as a whole is very simple, and the final product has a much higher quality.

So, next step is to replace the plastic fermenter with a steel one. To be continued…

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