Pressure Fermentation Calculator
Pick a style and get a spunding plan: the valve setting for each stage, when to raise it, and the pressure to carbonate after the crash.
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Pressure fermentation settings by beer style
Pressure changes what the yeast makes: CO₂ held in the beer slows the fruity esters and hot fusel alcohols. Clean styles go under pressure after the first day or two, hop-forward beers take a moderate amount, and ester-driven styles like hefeweizen, saison and English ales stay open until fermentation is nearly done. The reasoning, style by style, is in pressure fermentation for every ale style.
| Style | First 1–2 days | Active | End of fermentation | Carbonation | Use pressure? |
|---|---|---|---|---|---|
| Lagers fermented warm (62–68°F) | 0–2 psi | 10–15 psi | 12–15 psi | 2.5–2.7 vol | Yes: the best case |
| Kölsch, cream ale, blonde ale | 0–1 psi | 5–10 psi | 8–12 psi | 2.4–2.7 vol | Yes |
| Pale ales, IPAs, hazy IPAs | 0–1 psi | 5–8 psi | 8–10 psi after the last dry hop | 2.4–2.6 vol | Yes, moderate |
| Amber, brown, red, Scottish ales | 0–1 psi | 2–4 psi | 5–8 psi | 2.0–2.3 vol | Light |
| Stouts and porters | 0–1 psi | 4–6 psi | 6–8 psi | 2.0–2.4 vol | Moderate |
| Imperial stout, barleywine, double IPA | 0–1 psi | 4–6 psi | 6–8 psi | 2.0–2.3 vol | Yes: fewer fusels |
| English ales | 0 psi | 0 psi | 1–2 psi near the end | 1.8–2.0 vol | No, until the end |
| Belgian ales and saison | 0 psi | 0 psi | 1–2 psi, optional | 2.6–3.0 vol | No, until the end |
| Hefeweizen and witbier | 0 psi | 0 psi | 1–3 psi near the end | 3.0 vol and up | No, until the end |
Carbonation chart
Gauge pressure in psi at sea level. Add about 1 psi for every 2,000 ft of elevation. Give it about a week at the setting, or a day or two with a carbonation stone.
| Temp | 2.0 vol | 2.2 vol | 2.4 vol | 2.5 vol | 2.6 vol | 2.8 vol | 3.0 vol |
|---|---|---|---|---|---|---|---|
| 32°F0°C | 3 | 5 | 7 | 8 | 9 | 11 | 13 |
| 34°F1°C | 4 | 6 | 8 | 9 | 10 | 12 | 14 |
| 36°F2°C | 5 | 7 | 9 | 10 | 11 | 13 | 15 |
| 38°F3°C | 6 | 8 | 10 | 11 | 12 | 14 | 16 |
| 40°F4°C | 7 | 9 | 11 | 12 | 13 | 16 | 18 |
| 42°F6°C | 8 | 10 | 12 | 13 | 14 | 17 | 19 |
| 45°F7°C | 9 | 11 | 14 | 15 | 16 | 18 | 21 |
| 50°F10°C | 11 | 14 | 16 | 18 | 19 | 21 | 24 |
Questions
What psi should I ferment at?
Leave the valve open or at 0–2 psi for the first 24 to 48 hours. After that, 10–15 psi for lagers fermented warm, 5–10 psi for clean ales and IPAs, and 4–8 psi for stouts, porters and big beers. Keep English, Belgian and wheat beers open until fermentation is nearly done. The calculator gives the setting for each stage.
When should I close or raise the spunding valve?
A few gravity points before final gravity. The yeast makes about 0.5 volumes of CO₂ per gravity point, so 2 to 5 points is usually enough to bring the tank up to your setting. Raising it early does no harm to a clean beer: once the tank reaches the setting, the valve vents the rest.
Can I fully carbonate in the fermenter?
Yes, but do it cold. At fermentation temperature, full carbonation takes more pressure than a 15 psi relief valve allows. Spund to 10–15 psi, cold crash, then set the gas from the chart: about 10 psi at 34°F gives 2.5 to 2.6 volumes.
Does pressure fermentation work for every beer?
No. It shines in lagers, kölsch, cream ales, IPAs and big beers. Saison, hefeweizen, Belgian ales and English ales get their character from esters and phenols that pressure suppresses, so ferment them open and only seal the tank near the end to carbonate and keep oxygen out.
Why does the gauge drop when I cold crash?
Cold beer absorbs more CO₂, and the gas in the headspace contracts. Without a CO₂ line connected, the tank can go below zero and pull air in. Hook up the gas at the pressure from the chart before you start cooling.
What fermenter do I need?
One with a stated working pressure and a relief valve. Buckets, carboys and most plastic fermenters can’t hold pressure. Our Unitank is rated to 30 psi working pressure and ships with a 15 psi relief valve; add an adjustable spunding valve (0–2 bar, 0–29 psi).