Two modes
Carbonation stones work in two modes:
- Hydrophobic (beverage-hating): bubbles are manufactured on the outside of the stone.
- Hydrophilic (beverage-loving): bubbles are manufactured on the inside of the stone.
The terms come from surface science: a hydrophilic surface is one a liquid readily wets, and a hydrophobic surface resists wetting (LibreTexts).
In hydrophilic mode, the bubble is born inside the stone and comes out the same size as the pores. Small pores, small bubbles, and carbonation happens. In hydrophobic mode, the flow rate is turned up and multiple pores merge into one bubble at the surface: big bubbles that don’t dissolve. Those bubbles are no good.
The pressure-drop trick
A ceramic stone has a thick wall, which creates a big pressure drop from inside to outside. As long as you don’t exceed that drop, the beverage stays wetted in the stone, keeping it in beverage-loving mode. That’s why ceramic is hard to push into hydrophobic.
Ceramic vs. stainless steel
| Ceramic | Stainless steel | |
|---|---|---|
| Hydrophobic resistance | Very hard to push hydrophobic (thick wall, big pressure drop) | Easy to flow hydrophobic |
| Durability | Fragile; drops tend to break it | Durable, but wears out and corrodes over time |
| Cleaning | Harder to clean (see our cleaning guide) | Easier, but never brush sintered stainless (GW Kent) |
The flow rule
For most carbonation stones, keeping flow at or below roughly 0.8 cubic feet per hour per inch of stone keeps them in hydrophilic mode. On a 12-inch stone, that’s a ceiling of about 9.6 CFH. For your own tank and stone, BrewWizz’s Stone Flow Rate Calculator estimates a recommended flow rate and carbonation time. And remember why it matters: small bubbles don’t reach the top, so small bubbles cannot scrub your product. That’s especially important for very hoppy beers or beers that need a lot of head. The best way to know your stone’s behaviour is the data FizzWizz logs in the cloud; see Anatomy of a Perfect Carbonation Plot for how to read it.
Not sure which stone suits your tank? Contact us. We regularly help brewers match stones to their tanks.