Fermenting in a keg: Guide to turning your keg into a pressure fermenter

1. The golden rules of volume and primary fermentation

Fermenting in a traditional Soda Keg or an Oxebar vessel requires following the same biological rules as in a classic fermenter, with particular attention paid to dimensions:

• Managing headspace: This is the main constraint. During the active phase of fermentation, foam formation (krausen) needs space so it doesn’t block the gas outlets. You must keep at least 2 liters of empty space at the top of your keg. For a standard 19‑liter keg, never exceed 17 liters of wort.
• Starting with a blow‑off: During the first days of primary fermentation, yeast activity is extremely vigorous. To evacuate the massive CO₂ flow without risking clogs, install a blow‑off line (a tube submerged in a container of sanitised water) connected to your grey gas post.

2. Switching to pressure and managing it with a spunding valve

The huge technical advantage of the keg lies in its ability to withstand high pressure, opening the door to advanced end‑of‑fermentation management:

• Natural carbonation: Once the most violent part of primary fermentation has passed, you can remove the blow‑off and install a spunding valve (adjustable counter‑pressure valve) on your gas post. By tightening it to hold gas at the desired pressure, the beer will carbonate itself thanks to the CO₂ produced during the final yeast activity. Once fermentation is complete, your beer is already sparkling!
• Direct serving: Since your beer fermented and carbonated in the same vessel, it is theoretically ready to be served directly from that keg, avoiding any intermediate handling or oxidation risk.

3. Essential modifications for sediment‑free serving

Because fermentation takes place inside the keg, all yeast and hop debris (sediment) will accumulate at the bottom. With a standard setup, the stainless dip tube would suck up this sediment from the very first pour. To avoid this, two accessories make all the difference:

The stainless floating dip tube: Top‑draw liquid pickup

To bypass the sediment issue, the best modification is to remove the original rigid dip tube and replace it with a stainless floating dip tube kit for Soda Kegs. Made of a flexible silicone tube and a floating stainless ball, this system ensures that beer is always drawn from the surface, where it is clearest, leaving the yeast sediment undisturbed at the bottom.

The inline filter: The anti‑clog shield

If you perform dry hopping directly inside your keg, small hop particles may float around and clog your Ball Lock connectors or serving tap. To secure your line, add a 6 mm inline filter to the end of your silicone tube. This fine mesh filter will trap even the smallest debris, ensuring smooth serving and perfectly clean beer.

4. Configuration table: From classic fermenter to KEG

To visualise the adjustments required when switching to keg fermentation, here is a summary of the technical parameters: