---
title: "What’s Happening in Your Tank: The Physics of Bubble Size"
url: https://getfizzwizz.com/bubble-size-physics/
date: 2026-10-05T22:07:15+00:00
modified: 2026-10-06T11:57:48+00:00
lang: en_US
---

# What’s Happening in Your Tank: The Physics of Bubble Size

This is the article that explains why "just turn the gas up" is wrong.

## How the FizzWizz is plumbed

The video opens with the setup, and each part plays a role in bubble size:

- **CO2 in:** supply from your pressure regulator, set to about 25 to 30 PSI.
- **Stone line:** a quarter-inch pneumatic hose from the FizzWizz to the top of your carbonation stone.
- **Separator:** connects the FizzWizz to the CIP arm, with a small sight glass at the bottom. More on why that matters below.
- **WizzTemp temperature sensor:** in its own dedicated thermowell, via a spare well, a thermowell adapter on the sample port, or the WizzStone-Combo. See [What Is a Thermowell](/what-is-a-thermowell/).

## The three controls on bubble size

1. **The size (length) of your carbonation stone**
2. **The pore size inside the stone**
3. **How fast you flow CO2 through the stone**. On FizzWizz, that's a flow controller measured in cubic feet per hour (CFH).

## Why small bubbles win

**Buoyancy.** Big bubbles are mostly gas, so they race to the headspace and never dissolve. Small bubbles barely rise; they linger in the beer, and lingering time is dissolving time.

**Surface area.** Fit many small bubbles in the space of one big one and you get far more gas-to-beer contact area for the same volume of CO2. It's the same reason crushed ice dissolves in a gin and tonic faster than one big cube.

**Laplace pressure.** Surface tension squeezes every bubble, and the smaller the bubble, the harder it squeezes. The extra pressure inside rises as the bubble shrinks (ΔP = 2γ/r, the Young-Laplace equation; see [LibreTexts](https://phys.libretexts.org/Bookshelves/Classical_Mechanics/Essential_Graduate_Physics_-_Classical_Mechanics_%28Likharev%29/08%3A_Fluid_Mechanics/8.02%3A_Surface_Tension_Effects)), and that extra pressure pushes CO2 out of the bubble and into solution. The effect only becomes large at microscopic sizes. Using a measured surface tension for lager of 55 mN/m ([Atasi et al.](https://arxiv.org/pdf/2211.02253)):

| Bubble diameter | Extra pressure inside (approx.) |
| --- | --- |
| 0.1 mm (just visible) | 0.3 PSI |
| 10 µm | 3 PSI |
| 1 µm | 32 PSI |
| 0.3 µm | 106 PSI |

Those micron sizes overlap with the pores in a fine stone; sintered stainless stones are sold with pores as small as 0.2 µm ([GW Kent](https://www.gwkent.com/replacement-12-stone.html)). A stone that releases bubbles close to its pore size gives you bubbles that want to dissolve.

**Depth.** The weight of the beer helps too, in a different way. Liquid depth adds roughly 1.4 PSI per metre, so the stone at the bottom of the tank sits at a higher pressure than the headspace.

## What happens when you flow too fast

In the video's animation, the FizzWizz runs in carbonation mode at its default of 2.4 volumes. At 1 CFH you get a fine cloud of tiny bubbles that dissolve locally, and almost nothing reaches the headspace. At 4 CFH the bubbles grow and more of them escape upward. At 8 CFH you get big lazy bubbles, foam on top of the tank, and poor transfer. Stouts and other highly foamy styles are especially punished: they need slower flow and smaller bubbles than, say, a pilsner.

## The sight glass: your only warning

In a real tank you cannot see foaming at the top. That's why the FizzWizz separator has a **sight glass**. If you see beer dripping into the sight glass, you are flowing far too fast. The fix is not to nudge it down: **cut the flow rate to at least half** and let the bubbles shrink back.

## And if you need to carbonate faster?

Don't turn the flow up. Get more small bubbles instead: a longer carbonation stone gives you more emission area, so you can run a higher CFH without creating big bubbles. Or add a second stone: the [Splitter-Wizz](https://www.brewwizz.com/products/splitter-wizz) runs two stones in one tank at the same time.

**Every stone is different.** [Contact us](/contact/) and we'll review your setup and help you dial in the right flow rate for your stone. For a quick estimate, try the [Stone Flow Rate Calculator](https://mobilebrewwizzdata.onesmartview.com/co2FlowRate).