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Aerating / Oxygenating Wort

 

Tools for aerating wort

 

Introduction

Most brewers realize that once fermentation is complete beer contact with oxygen must be limited to maximize shelf life and avoid having the beer turn stale, giving it a cardboard like taste. This is especially true with hop forward beers where any contact with oxygen can rob the beer of the delicate hop flavours and aromas, rendering it lifeless.

During the long and vigorous boil most of the oxygen that was dissolved into the wort solution will have been driven off which, based on the comment above, we would assume is a good thing. Unfortunately, to properly ferment wort and turn the sugars into alcohol creating the beer we know and love, yeast needs oxygen. Because of this there is one (and only one) point in the brewing process where oxygen contact is allowed and actually desirable: After the wort has been boiled and chilled down to fermentation temperature, ready for the yeast to be pitched.

This oxygen is used by the yeast for sterol synthesis which helps keep the cell walls pliant, an important aspect to cell growth and overall cell health. Without an adequate supply of sterols, yeast cells characteristically display low viability and poor performance in fermentation. Stuck or stalled fermentations, long fermentation times, slow fermentation starts which are prone to infection, under attenuated beers, yeast stress, and off-flavours are often the result of too little oxygen. Lowered yeast viability with each subsequent generation may also occur (important for brewers that like to reuse yeast).

To help the yeast thrive and ferment properly we therefore need to re-introduce dissolved oxygen to the wort after chilling right before the yeast is pitched. This is the one and only place in brewing where oxygen should be added to wort (or beer for that matter). This is done either through aeration (introducing oxygen via regular air) or oxygenation (adding pure oxygen from a tank). The pros and cons of each, the recommended oxygen levels, as well as the approaches we use are documented below.

Want to learn more about the science behind all things yeast related? Refer to the excellent (and comprehensive) book Yeast: The Practical Guide to Beer Fermentation. A must-have for any brewer looking to maximize the quality and consistency of their beer.

Manufacturers of active dry yeast (such as Fermentis, makers of Safale US-05 and Saflager W-34/70) may indicate that aeration or oxygenation is not required as their yeast is rich enough in sterols (lipids) and minerals for its own multiplication process. When in doubt, there is certainly no harm in aerating or oxygenating anyway. When repitching (reusing) dry yeast the wort should always be aerated or oxygenated

 

Shop control panel kits and parts

 

Recommended dissolved oxygen levels

8 ppm (parts per million) of dissolved oxygen in wort is considered the minimum level that should be achieved before the yeast is pitched, but beers with higher yeast demands (such as lagers, hybrid beers, and high gravity ales) may benefit from more. In other words, the more yeast you pitch per volume of wort, the higher the recommended level of dissolved oxygen. Yeast pitch rates and recommended dissolved oxygen levels are included in all of our recipes. More on yeast demands can be found in our Making a Yeast Starter guide.

Our recommended dissolved oxygen levels and methods to implement are as follows:

Yeast strain / Gravity Recommended dissolved oxygen level Method
Ale strains up to 1.060 8 ppm 120 seconds with an agitating rod
- or - 
Pure oxygen at a rate of 1 litre per minute for 60 seconds per 5 gallons
Ale strains above 1.060, all lager / hybrid strains (Kolsch, Altbier, California Common) up to 1.060 14 ppm Pure oxygen at a rate of 1 litre per minute for 120 seconds per 5 gallons
Ale strains above 1.100 and all lager / hybrid strains above 1.060 14 ppm, plus a second dose of 14 ppm 12-18 hours after the yeast is pitched (the time required for at least one cell division to have occurred) Pure oxygen at a rate of 1 litre per minute for 120 seconds per 5 gallons (twice)

Below are different products we use for achieving these recommended dissolved oxygen levels, along with our recommendations.

The actual dissolved oxygen level will vary based on the exact equipment used, how it's used, wort gravity, wort temperature, and even fermenter geometry. To confirm actual dissolved oxygen levels, use a dissolved oxygen meter and then adjust accordingly.

 

Parts and tools

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Fizz-X wort agitating rod

Fixx-X wort agitating rod

The simplest method to add oxygen to wort, practiced by many home brewers, is to simply vigorously shake or stir the wort (given enough time and backbreaking work).

We employ a similar but simpler method that takes less time, using a Fizz-X wort agitating rod (looks like a paint stirrer) on the end of a hand drill running at high speed. These agitating rods are sold under various names such as 'Degas-X', 'Fizz-X', and 'Brewgas Whizz Stick' and were originally sold for de-gassing wine. Made out of stainless steel and nylon, they are durable and easy to clean and sanitize.

The trick is to create a large funnel and churn air into the wort by making sure the nylon rods on the end are partially exposed to air. 


After there will be many inches of thick / dense foam on top of the wort. The domed lid with a 3" tri-clamp fitting on our stainless steel fermentation buckets helps keep the spinning wort in the vessel.

Because air is only 21% oxygen the maximum dissolved oxygen a brewer can achieve using an agitating rod is approximately 8 ppm, our minimum recommended concentration for ales up to 1.060. Approximately 120 seconds is all that is required to reach 8 ppm.

We prefer and use this agitating rod method of aeration whenever possible as it is quick and requires a minimal amount of cleaning or maintenance. When higher than 8 ppm dissolved oxygen is required pure oxygen must be used.

 

Atmosphere based aeration system with pump and diffusion stone

Atmosphere based aeration system with pump and diffusion stone

An atmosphere based aeration system with pump and diffusion stone can also be used to aerate wort. A pump is used to push air through tiny holes in the stainless steel diffusion stone to create small bubbles.

Similar to the agitating rod method (described above), the maximum level of dissolved oxygen is around 8 ppm as we are still only using atmosphere with 21% oxygen.

Atmosphere based pump aeration systems require 30-120 minutes to reach a level of 8 ppm, and are therefore considerably slower than the agitating rod method which only takes 120 seconds. While a stone with smaller holes such as a 0.5 micron stone would speed up the aeration (small bubbles provide more surface area for diffusion), these simple pumps do not provide enough pressure so larger 2 micron stones must be used.

Extended aeration can be detrimental to head formation and retention. Care must be taken when handling the diffusion stone as simple hand greases can clog the tiny pores. The sanitary air filter also requires periodic replacement.

We do not recommend atmosphere based pump aeration systems due to the extra work and care required, and because the wort spends extra time prone to dust borne wild yeast and bacteria taking hold before our yeast is pitched. The agitating rod method is considerably quicker and simpler and provides similar results when only 8 ppm is required. 

 

Pure oxygen based oxygenation system with tank and diffusion stone

When higher than 8 ppm of dissolved oxygen is required, pure oxygen is the only choice. Since 100% oxygen is used (instead of atmosphere with only 21% oxygen) higher levels of dissolved oxygen can be achieved.

The time required when using pure oxygen is also greatly decreased as unlike atmosphere based pump systems which must use a 2 micron stone, compressed oxygen tanks provide enough pressure such that a 0.5 micron stone can be used instead. A 0.5 micron stone produces smaller bubbles which provide more surface area for diffusion, speeding up the rate at which the wort absorbs oxygen. Oxygenation with pure oxygen is quick and only takes 60-120 seconds with a 0.5 micron stone.

The downside to using pure oxygen is the added cost of equipment (tanks, regulator, flow meter, diffusion stone), tanks require periodic refilling (or replacing if disposable), and care must be taken when handling and cleaning the diffusion stone as simple hand greases can clog the tiny pores. The sanitary air filter also requires periodic replacement (if your system uses one that is, not all do as technically you shouldn't need one with pure oxygen from a tank). While too much oxygen is rarely an issue, over-oxygenation is also possible and may result in undesirables such as fusel alcohols, increased acetaldehyde, and other flavour problems.

Pure oxygen is usually dispensed from either larger refillable oxygen tanks or smaller pre-filled disposable oxygen tanks. Both provide similar results.

A pure oxygen based system with refillable tank, regulator with flow control, sanitary air filter, stainless steel wand, and 0.5 micron stoneA pure oxygen based system with refillable tank, regulator with flow control, sanitary air filter, stainless steel wand, and 0.5 micron stone

A pure oxygen based system with pre-filled disposable tank, regulator, flow meter, and 0.5 micron stoneA pure oxygen based system with pre-filled disposable tank, regulator, flow meter, and 0.5 micron stone

Which sort of tank system you choose is entirely up to you.

Refillable oxygen tanks are purchased empty and come in various sizes anywhere from approximately 1.5 to 150 cubic feet (42-4248 litres). They are initially more expensive, require periodic filling and recertification, but will cost less in the long run than 1.1 cubic foot (31 litre) pre-filled disposable oxygen tanks, especially when a larger size is used. For safety reasons we highly recommend an oxygen tank cart or stand be used with larger refillable tanks. 

Oxygen tanks come with different fittings requiring different regulators to control the flow of oxygen. Refillable oxygen tanks use either CGA-540 (industrial/commercial) or CGA-870 (medical/home health) fittings, while disposable oxygen tanks use CGA-601. Make sure to purchase a regulator that matches your oxygen tank as they are not interchangeable.

Before purchasing a refillable oxygen tank do your homework and ensure that you have shops available that can fill for you. Disposable oxygen tanks are more common, and the disposable nature means you'll never run out of oxygen (as long as you always keep a spare). That said, purchase one of the larger refillable tanks and you'll have enough oxygen for literally thousands of homebrewing sized batches.

Regulators for refillable oxygen tanks usually include a dial that allows you to set the exact rate of flow, while regulators for disposable oxygen tanks do not. If using disposable oxygen tanks a separate oxygen flow meter in-line with the 3/16" ID vinyl (PVC) tubing needs to be used to see the exact flow rate. The flow meter uses a floating ball and gravity to measure flow and therefore must be kept vertical. We recommend an oxygen flow meter that reads up to 1.5 litres per minute. 3/16" tubing will fit over 1/4" barbs by first heating the tubing in hot water. To ensure a tight seal use hose clamps (5/16" to 7/8" diameter hose).

If using an oxygen regulator with built-in flow control it's best to use one meant for brewing as the flow rate adjustment range is tuned to allow finer control at the low end where we need it (typically 1 litre per minute). For example, the Blichmann oxygen flow regulator has presets for 0.1, 0.25, 0.5, 0.75, 1, 1.5, 2, 4, and 7 litres per minute. Most industrial or medical oxygen regulators are designed for higher flow rates (up to 15-25 litres per minute) and may have presets that are not as accurate at the low end.  

When using pure oxygen position the 0.5 micron stone as low as possible in the fermenter and slowly circulate, while maintaining a low and consistent flow rate. The goal is to minimize the amount of bubbles you see at the surface as that is wasted oxygen that hasn't been absorbed by the wort. Keeping the stone low is simplified by using a stainless steel oxygenation wand on the end of 3/16" ID vinyl (PVC) tubing. To ensure a tight seal use hose clamps (5/16" to 7/8" diameter hose).

Some brewers choose to add pure oxygen in-line immediately after their wort chiller, through a 1/2" NPT 0.5 micron stone installed in a 1/2" NPT stainless steel tee fitting. This method is difficult to implement with any consistency as the two flow rates (pure oxygen and wort) must be carefully controlled to avoid inconsistent oxygenation. We recommend instead that pure oxygen be added after the wort is in the fermenter as it is easier to control the level of dissolved oxygen.

While pure oxygen can certainly be used for all beers, we only use it for ales with gravity above 1.060 and all lagers, or when high attenuation is required. For lower gravity ales we prefer the simpler agitating rod method of aeration.

Pure oxygen is highly flammable. Ensure you read and follow the safety precautions outlined in the documentation that was included with your oxygen tank and regulator.

 

Milwaukee MW600 dissolved oxygen meter

Milwaukee MW600 dissolved oxygen meter

Different equipment, wort gravity, wort temperature, and even fermenter geometry means that dissolved oxygen levels are difficult to predict and can never be guaranteed. Want to know how much dissolved oxygen you actually have in your wort after aeration / oxygenation? Use a dissolved oxygen meter.

Dissolved oxygen meters have historically been very expensive but over the years have come down enough in price such that serious homebrewers now use them to confirm their wort dissolved oxygen levels before pitching yeast. We recommend the Milwaukee MW600. Using a meter allows the brewer to measure levels and adjust to remove inconsistencies from batch to batch.

The Milwaukee MW600 uses a polarographic probe (no stirring or agitation is required) and supports two-point manual calibration and automatic temperature compensation for greater accuracy.

The probe uses an oxygen-permeable polytetrafluroethylene (PTFE) membrane sensor that requires periodic replacement. When it becomes wrinkled or has stretch marks, it's time to replace it. See Milwaukee MA841 spare membrane. We suggest picking up an extra bottle of Milwaukee MA9071 oxygen electrolyte solution (used for calibration) at the same time.

Milwaukee MA9071 electrolyte calibration solution and MA841 spare membranesMilwaukee MA9071 oxygen electrolyte solution and MA841 spare membranes