How Is Dissolved Oxygen Measured in Beer?

Oxygen is both a blessing and a curse in the brewing process. Without oxygen, yeast would not be able to ferment. With too much oxygen, beer ends up tasting off.

For this reason, it is critical for a brewer to understand not only the value of dissolved oxygen in beer but also how to manage and measure it.

What Is Dissolved Oxygen in Beer?

To understand dissolved oxygen in beer, you must first remember the brewing process and its essential ingredient – yeast.

After all, beer was more a discovery than an invention.

Beer is, at its most basic, fermented grain water.

The most ancient recipes involve toasting grains and boiling them in water, filtering out the grains and leaving the cooled wort exposed to the elements.

At that point, wild local yeast will be naturally attracted to the natural sugars in the wort, consume those sugars for energy, and then produce alcohol and carbon dioxide as a waste byproduct.

Then (and this started happening more recently). hops are added to cut down on the sweetness in the beer.

Today, the process is not much more complicated than it was thousands of years ago.

There are a few more steps, like sparging and racking, or secondary fermentation, as we have come to comprehend fermentation on a deeper level, but at its most basic, beer is simple.

What many people don’t realize is how critical oxygen is to the process.

First, yeast needs oxygen to ferment. It can only ferment for a very short period of time without oxygen before getting stressed out and dying off. If you have any hope of saving your yeast for a later batch, you don’t want it to die.

Of course, in ancient times, brewers allowed nature to take its course.

Yeast had access to dissolved oxygen in the beer because the vessel was left open to the air. Then, as carbon dioxide was created through fermentation, along with the krausening, a protective cap was formed on the top of the fermenting beer, locking out new oxygen from entering the beer, and locking in the existing dissolved oxygen already in the beer.

Further, the beer was generally drunk within a few days, a maximum of a week or two, from the time it was fermented.

So, fear of off flavors and characteristics was never a concern.

Effects of Dissolved Oxygen in Beer

Today, of course, brewers, even small, craft brewers, have to consider their beer may not be drunk for several weeks or even months from the time of fermentation.

The more oxygen the beer is exposed to, the more oxidation can take place, which interferes with the smoothing out and cleaning up process beer undergoes once fermentation is complete.

Because we are now planning for a longer-term beer, it is essential that we maintain tight control over dissolved oxygen over beer at every point.

How Is Dissolved Oxygen Measured in Beer?

Brewers are now encouraged to test dissolved oxygen levels at every point along the fermentation process, from before fermentation to during and during every step after fermentation.

The ideal dissolved oxygen level for beer before fermentation is between 8 and 12 PPM, with 5 being the lowest and 17 being the highest.

After fermentation, you want your DO levels to be down to .2 PPM and even lower so as not to interfere with secondary fermentation and filtration.

The measurement process typically involves sensors called dissolved oxygen meters that involve a chemical detection called polarography.

Electrodes are placed in the solution and a voltage is applied, which generates a current. This electrical process allows the sensors to then measure the DO in the solution and provide that measurement to the reader.

Managing Dissolved Oxygen in Beer

Before fermentation, there is not much to do in managing oxygen levels. Yeast is happy and healthy with plenty of oxygen. Still, it is a good idea to measure your oxygen levels at this point, so you have a starting point with which to work.

Once fermentation has begun, however, you will want to limit the wort/beer access to oxygen.

To manage your dissolved oxygen levels, pay attention to areas that may allow oxygen to get into your beer.

During carbonation, oxygen can enter beer through lines or as vessels or tanks are opened or beer is transferred.

During filtrations, your dissolved oxygen levels will naturally increase as beer passes through the filter and then should decrease again as filtration continues.

If you add stabilizers to your beer, be aware that this step is one in which oxygen levels may increase.

Packaging is the final step, and the most concerning area where DO can be increased.

When DO is allowed to enter the bottle with beer, you stand to have a much shorter shelf life as oxygen will wear down, or oxidize the bright, crisp, clean flavors and aromas in beer and result in a flat, flavorless product over time.

If there is any part of the brewing process where you want to minimize oxidation, it is during packaging or bottling.

In the end, having an accurate dissolved oxygen sensor to take continuous readings throughout the brewing process will help you get an accurate intuition for where and when you can manage dissolved oxygen levels in your beer and catch areas where oxygen may be entering your beer.

Quite often, brewers find leaks or pinholes in lines that can be repaired. Another common trick is to ensure your beer maintains a temperature that is cool enough to still produce a foam cap. That carbon dioxide on the beer will act protectively against new DO entering your beer.

Again, it is all about experimenting and fiddling around with your process using sensors that let you know what is going on.

Cheers!

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Sources:

1. https://www.brewer-world.com/control-of-dissolved-oxygen/
2. https://brewingindustryguide.com/managing-dissolved-oxygen-levels/
3. https://byo.com/article/testing-dissolved-oxygen/

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