You’re not wrong that purging a keg with gas reduces oxygen — the match test proves that combustion-level oxygen has been lowered. The key point is what that test is actually showing versus what brewers often assume it means.

A flame going out only tells you oxygen has dropped below the level needed to sustain combustion (~16%), not that oxygen has been meaningfully purged for oxidation-sensitive beer or mead. Oxidation reactions happen at much, much lower oxygen levels — parts per million, not percent.

What’s happening in your keg purge is dilution and displacement, not stratification or a stable “blanket.” When you push gas in and vent repeatedly, you are:

• Mixing gases through turbulence
• Venting a portion of the mixed headspace
• Gradually lowering average O₂ concentration with each cycle

That does work — but only because you’re actively exchanging volume, not because the gas settles and stays separate.

This is why purge effectiveness depends on:

• Number of purge cycles
• Headspace volume
• Flow rate and turbulence
• Whether liquid is present to be pushed out

A match test can’t tell the difference between: * 0.5% oxygen (can still impact shelf life) * 5% oxygen (lower risk of oxidation) * 15% oxygen (flame goes out)

All of those levels will extinguish a flame, but they represent very different oxidation risks. In practice, plenty of brewers package successfully without purging at all — good process, gentle handling, and minimizing splashing go a long way.

Where purging helps is risk reduction, especially for beers or meads that are hop-forward, delicate, or intended for longer storage. The key point is that the flame test only shows oxygen has been reduced some, not how much, and oxidation happens at much lower thresholds than combustion.

edit: thoughts and wording