---
title: "What’s Happening in Your Tank: The Physics of Bubble Size"
url: https://fizzwizz.ca/bubble-size-physics/
date: 2026-10-05T22:07:15+00:00
modified: 2026-10-05T22:07:15+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.

## 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.** A small bubble surrounded by beer is squeezed by the weight of liquid above it. The smaller the bubble, the higher the internal pressure: a bubble the size of a cat's whisker can hold 30 to 100 PSI inside. That pressure differential is what drives CO2 into solution. (Look up "Laplace pressure" if you want the full derivation.)

## What happens when you flow too fast

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.

**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.