---
title: "Pre-Scrub: Knocking Out Oxygen Before You Carbonate"
url: https://fizzwizz.ca/pre-scrub-dissolved-oxygen/
date: 2026-10-15T07:41:39+00:00
modified: 2026-10-15T07:41:39+00:00
lang: en_US
---

# Pre-Scrub: Knocking Out Oxygen Before You Carbonate

Pre-scrub is an optional step FizzWizz can run before carbonation. If oxygen pickup in your cellar is something you worry about, it's worth understanding what it does and when to use it.

## Why oxygen matters after fermentation

Once fermentation is done, oxygen is the enemy of shelf life. Nova Scotia's Perennia sums up flavour stability as "keep oxygen out and keep it cold", and says cold conditioning is the stage to make sure beer has its lowest possible dissolved oxygen ([Perennia, Brewing Stability fact sheet](https://www.perennia.ca/wp-content/uploads/2023/01/Brewing-Stability.pdf), citing Bamforth's ASBC guide to beer freshness).

Transfers, pumping and filtration can all add oxygen. Press filtering is one example.

## What the pre-scrub does

![Bubbles rising through a tank carry oxygen into the headspace, which then vents out the CIP arm.](https://fizzwizz.ca/wp-content/uploads/2026/10/04-inline-pre-scrub-diagram-1024x683.jpg)

Here's what it does:

1. Once the product reaches its start temperature, FizzWizz dissolves about 3 PSI of CO2 into the product.
2. It then vents the tank down to 1 PSI over 20 to 30 minutes, out through the CIP arm.
3. Carbonation then starts on its own.

The idea is that the first dilution is always the greatest. CO2 bubbling through the product carries freely available oxygen into the headspace, and venting sends it out of the tank. You don't have to do any of this by hand: you select pre-scrub after setting the start temperature, and FizzWizz runs it automatically.

On a plot, you'll see the tank pressure climb to about 3 PSI, ease down to 1 PSI, then rise again as carbonation begins. See [Anatomy of a Perfect Carbonation Plot](/perfect-carbonation-plot/) and, for a warm-arriving product, [Carbonating Kombucha, Pop, and Cider](/kombucha-pop-cider-carbonation/).

## When to use it

Our advice: pre-scrub is a good idea if you use press filtering and are worried about dissolved oxygen. If you're not sure how much oxygen your process picks up, measure it first (see below).

## What pre-scrub doesn't do

Pre-scrub works on oxygen that's freely available in the product when it reaches the bright tank. It doesn't undo oxygen picked up later, during packaging. Perennia's checklist covers that stage separately: low-air filling equipment and protocols, oxygen-scavenging crowns, and proper can seaming.

## Measure it

If oxygen matters to your product, measure dissolved oxygen before and after the pre-scrub on a few batches. Numbers from your own cellar will tell you more than any rule of thumb.

**Questions about pre-scrub on your setup?** [Contact us](/contact/).

## Sources

- Perennia, [Brewing Stability Fact Sheet: Minimizing Flavour Changes in Beer](https://www.perennia.ca/wp-content/uploads/2023/01/Brewing-Stability.pdf) (January 2023), citing Bamforth, *Practical Guides for Beer Quality: Freshness* (ASBC, 2017).
- [Anatomy of a Perfect Carbonation Plot](/perfect-carbonation-plot/) (pre-scrub steps, press filtering advice).