How to Aerate Wort: Oxygen for Yeast, Methods and How Much
Yeast need oxygen at the start of fermentation, and boiled wort has almost none. Why to aerate chilled wort, how much oxygen to aim for, and how splashing, air pumps and pure oxygen compare.
In this post
The short answer: aerate wort once, right after you chill it and before or as you pitch the yeast. Yeast use that oxygen to build healthy cell walls and multiply, which gives a faster start and a cleaner fermentation. Boiling drives almost all the oxygen out, so you have to put it back. Aim for about 8 to 10 ppm for most ales and 10 to 12 ppm for lagers and strong beers. After fermentation starts, oxygen is the enemy: keep it out.
Aeration methods compared
| Method | Roughly how much oxygen | Good for |
|---|---|---|
| Splashing the wort into the fermenter | Some, hard to control | Better than nothing |
| Shaking or stirring hard for a few minutes | Up to about 8 ppm | Small batches of normal-strength ale |
| Air pump with a filter and stone | Up to about 8 ppm; air is only 21% oxygen | Ales, if you’re patient (20 minutes or more) |
| Pure oxygen through a stone | 10 to 12 ppm or more in a minute or two | Lagers, strong beers, any batch you want to start fast |
| Inline oxygen into the wort line after the chiller | Precise and repeatable | Larger batches and pumped transfers |
How to aerate with pure oxygen
- Chill the wort to pitching temperature first. Cold wort holds far more oxygen than warm wort.
- Sanitize a 0.5 micron stainless stone. Our carbonation stone doubles as an oxygenation stone.
- Connect it to an oxygen regulator, using oxygen sold for food or beverage use.
- Open the flow gently, until you see a stream of fine bubbles without big foam.
- Give 5 gallons about a minute, a little longer for lagers and strong beers, then pitch.
Inline, the way breweries do it
With a pump and a counterflow chiller, you can put the stone in a tee in the wort line just after the chiller, ideally before a sight glass so you can watch the bubbles. Start the oxygen low and open it until you see small bubbles flowing with the wort, with the stone always covered. Every drop of wort gets the same dose on its way into the fermenter. Our counterflow chiller and tri-clamp fittings make this easy to plumb.
Aeration vs oxidation
| When | Oxygen is | Why |
|---|---|---|
| Hot wort | Keep it low in the mash; little concern in the boil | Mash-temperature wort still holds some oxygen and heat speeds up oxidation; boiling wort holds almost none. See is hot side aeration a myth? |
| Chilled wort, before pitching | Good | The yeast use it up within hours |
| Once fermentation is under way | Bad | It stales the beer, dulls hop aroma and shortens shelf life |
More in our guides to why yeast need oxygen and keeping oxygen out after fermentation.
Frequently asked questions
Do I need to aerate if I use dry yeast?
Less so. Dry yeast is produced with plenty of stored reserves, so a normal-strength ale will ferment fine without extra oxygen. Liquid yeast, lagers and strong beers benefit most.
Can I over-oxygenate?
It’s possible with pure oxygen, which can push levels high enough to stress the yeast. Stick to about a minute for 5 gallons.
Is an aquarium pump safe?
Yes, with an inline air filter to keep dust and microbes out, but it can only reach about 8 ppm because air is mostly nitrogen.
When should I aerate?
After chilling, right before or as you pitch. Never after fermentation has started.