Spunding Valves: The Homebrewer’s Secret Weapon

If you walk into a professional German brewery, you won’t see tanks hooked up to CO2 bottles for carbonation. You will see “spundapparat”—spunding valves.

For homebrewers, the spunding valve is one of the most versatile and cost-effective upgrades you can make. It allows you to carbonate your beer naturally (saving money), ferment under pressure (suppressing off-flavors), and perform safer closed transfers.

What is a Spunding Valve?

At its core, a spunding valve is an adjustable pressure relief valve (PRV).

You attach it to the gas post of your fermenter (or keg). You set a target pressure (e.g., 15 PSI). If the pressure inside the vessel exceeds 15 PSI, the valve opens and vents the excess gas. If it is below 15 PSI, the valve stays closed, keeping the gas inside.

Use Case 1: Natural Carbonation

This is the traditional use. During fermentation, yeast produces massive amounts of CO2. Usually, we let this blow off through an airlock.

By replacing the airlock with a spunding valve towards the end of fermentation, you trap that CO2 in the beer.

The Benefits:

Better Foam: Natural carbonation creates finer, longer-lasting bubbles compared to force carbonation (“carbonic bite” is often lower).
Aromatics: You aren’t “scrubbing” delicate hop aromas out of the beer by letting vigorous CO2 escape.
Free CO2: You use less gas from your tank.

The Method:

Ferment as normal until you are about 4-5 gravity points from your final gravity.
Remove the airlock/blowoff tube.
Attach the spunding valve.
Set it to the pressure required for your desired carbonation level (consult a carbonation chart based on your temperature).
- Example: At 68°F (20°C), you need about 25 PSI to get 2.4 volumes of CO2.

Use Case 2: Pressure Fermentation

Used primarily with Lagers and some IPAs. By fermenting under pressure (10-15 PSI) from day one (or day two), you suppress the yeast’s production of esters (fruity flavors) and precursors like VDKs.

Why do this?

Warm Lagering: You can ferment a lager at ale temperatures (68°F/20°C) without it tasting fruity. This speeds up lager production from months to weeks.
Suppressed Krausen: Pressure keeps the foam (krausen) lower, allowing you to ferment more beer in the same size vessel without blowoff messes.

Use Case 3: Oxygen-Free Transfers

This is crucial for NEIPAs. When you transfer beer from a fermenter to a keg, you want to avoid opening the lid.

Connect the spunding valve to the keg’s gas post.
Connect a jumper line from the fermenter liquid out to the keg liquid out.
Push beer from the fermenter using CO2.
As beer fills the keg, it needs to displace the gas inside. The spunding valve releases this gas while maintaining back-pressure. This prevents foaming during transfer and keeps the entire system sealed.

Types of Spunding Valves

1. Diaphragm Valve (e.g., Blichmann, BlowTie)

Pros: Extremely accurate. Uses a diaphragm to regulate pressure. Usually has a built-in gauge.
Cons: Slightly more expensive ($30–$50).
Verdict: The best choice for fermentation.

2. Poppet/Spring Valve (traditional brass style)

Pros: Cheap, rugged.
Cons: Not very accurate at low pressures. Can get “sticky” (hysteresis).
Verdict: Okay for holding pressure in a keg, but risky for sensitive fermentation control.

Safety Warning

NEVER put a spunding valve on a glass carboy. Glass cannot handle pressure and will explode, causing serious injury. Only use spunding valves on:

Corny Kegs
Stainless Steel Conicals rated for pressure (e.g., Unitanks)
Pressure-rated PET fermenters (e.g., FermZilla, All Rounder)

Conclusion

For under $50, a spunding valve (especially a BlowTie style) gives you control over carbonation texture, fermentation speed, and oxygen exposure. It is the gateway to “pro-level” process control on a homebrew scale.