How to Pressure Ferment Beer

What you need

Four items, and none is optional

1. A vessel explicitly rated for pressure. A FermZilla with its pressure kit, a KegMenter, a Spike CF conical, or a unitank. Not a Brew Bucket, not a bucket with a modified lid. This is a safety requirement, not a preference.
2. A spunding valve. An adjustable pressure relief valve, usually with a gauge. You set it to your target pressure and it vents anything above that. Without one, a sealed vessel has no relief path and will reach its limit.
3. Ball lock posts and disconnects on the vessel, plus a liquid-to-liquid jumper line for the transfer.
4. A CO2 supply with a regulator. You need it to purge the receiving keg and to push the transfer across.

Step 1

Let fermentation start at atmospheric pressure

Pitch as normal and leave the vessel vented -- spunding valve wide open or set very low -- for the first 12 to 24 hours. Yeast needs an unrestricted start to multiply, and applying pressure immediately suppresses the growth phase you actually want.

You will see krausen begin and the vessel start producing gas steadily. That is your cue.

Step 2

Set the spunding valve to 10-15 psi

Once fermentation is clearly active, set the spunding valve to your target. The yeast then pressurizes the vessel itself: CO2 accumulates until it reaches the setpoint, and the valve vents the excess.

You do not apply pressure from the gas bottle. The fermentation provides it. The spunding valve is a ceiling, not a pump.

• 10-12 psi for a clean ale fermented a little warm, or a first attempt.
• 12-15 psi for a lager yeast fermenting at ale temperatures, where you want maximum ester suppression.
• Above 15 psi gains nothing and starts costing attenuation and speed.

Step 3

Hold temperature as usual

Pressure widens the usable temperature window; it does not remove the need for a setpoint. Pick a temperature, hold it, and remember that the probe should read the beer rather than the air -- fermentation temperature control covers probe placement, which matters more than controller accuracy.

Pressure-fermented beers finish fast. Check gravity by sampling through the liquid post or reading a floating sensor; a flat curve for 48 hours is the signal.

Step 4

Cold crash -- sealed, which is the whole point

Drop to 32-38°F for 48 hours to pull yeast and protein out of suspension. On a pressure-rated vessel you simply leave it sealed under its residual pressure.

This is one of the clearest advantages of a rated vessel. An airlocked vessel cooling from 65°F to 34°F contracts, and it equalizes by drawing room air -- and airlock sanitizer -- back in through the airlock, introducing oxygen to finished beer at the moment it is most vulnerable. A sealed vessel under positive pressure cannot do that.

Step 5

Closed transfer to a purged keg

1. Purge the keg. The thorough method: fill the keg with sanitizer, seal it, and push the sanitizer out through the liquid post with CO2. The keg is then full of CO2 with no oxygen left. The quick method -- pressurize and vent several times -- is less complete but much better than nothing.
2. Connect liquid to liquid. A jumper line with a ball lock disconnect at each end, from the fermenter’s liquid post to the keg’s liquid post.
3. Vent the keg’s gas post slightly, or run a line from it back to the fermenter’s gas post. The beer flows from higher pressure to lower.
4. Control the rate. Slow is better. A fast transfer foams, and foaming in the receiving keg is lost carbonation and turbulence you do not want.
5. Stop when the flow changes. On a coned vessel you will see or hear it switch from beer to sediment.

The mechanism behind all of this is in pressure fermentation explained. If you do not have a keg setup yet, start with homebrew kegging setup, and if you want to ferment in the keg itself, fermenting in a keg.