The Importance of Dissolved Oxygen (DO) Meters for Brewing Beer

One of the oldest curated drinks known to man has now exploded across the world in the craft and hobbyist world. We’re talking about a good, hearty pint of beer. From light beer to dark beer, bitter to sour, sweet to spicy, beer now comes in a large variety of styles, aromas, and flavors. 

This article will focus on an important aspect of the beer brewing process, water and the dissolved oxygen levels in that water. If you’re looking more specifically at dissolved oxygen for other water applications, the Atlas Scientific blog has a variety of other topics around water quality and dissolved oxygen such as how to measure dissolved oxygen. On the other hand, if you’re interested in the role dissolved oxygen plays in the beer brewing process you’ve come to the right place.

What is beer made of?

The simple four-letter word beer is a perfect word to describe this four-component beverage. In the base form, beer consists of barley, hops, yeast, and water. And that’s it! Of course, there are plenty of variations in this simple chemical formula depending on the type of hops, the type of yeast, different additives, even different types of grains—like rice beer which is a great gluten-free alternative to regular beer. However, the base liquid water remains the same. The tried and true H₂O that contains our best friend dissolved oxygen, but potentially our worst enemy in the brewing process.

What is dissolved oxygen in water and beer?

Dissolved oxygen is exactly as it sounds, oxygen from the air or plants or O₂ tanks that dissolve directly into the water. Oxygen gas particles will dissolve directly into liquid water just like sugar or salt in an at-home experiment. This fundamental action in nature coins the dissolved oxygen term and helps us understand the general quality of water. Any water, tap water, lake water, ocean water, and our hot topic of the day, water for beer brewing.

You may be thinking, but isn’t water made up of oxygen? You are correct as well, since water is made up of two parts hydrogen and one part oxygen (H₂O) it does have oxygen in the base liquid. However, the big distinction here is that this one oxygen atom is bonded to two hydrogen atoms. So it cannot go floating around willy nilly and provide life to aquatic organisms or fuel yeast in the brewing process. 

Therefore dissolved oxygen is pure oxygen gas (usually in the form of O₂) that dissolves and fits between the individual H₂O water molecules. This phenomenon can even be seen with the naked eye in a glass of water left out in the sun. To continue, this free-floating dissolved oxygen is what supports aquatic life in natural waterways, and needs to be considered in practically all water applications (hydroponics, environmental sampling, fish farming, aquariums, brewing, etc). And this is the same dissolved oxygen in the beer-making process.

If you could care less about the science behind dissolved oxygen in water, just remember that dissolved oxygen provides fuel for yeast to metabolize sugar and create ethanol. However, it cannot exist in excess. So controlling these levels will be extremely important in the brewing process to find the dissolved oxygen sweet spot.

What is the beer making/brewing process?

The chemistry, tips and tricks, and in-depth details of the beer brewing process will not be included here. This section is purely for reference on where to implement an industrial dissolved oxygen meter or where to sample for dissolved oxygen.

That being said, considering the four ingredients (barley, hops, yeast, water) let’s dive into the high-level process following the schematic diagram.

1. The barley is malted (slightly germinated by a wet environment)
2. The malted barley is milled to remove the outer grain husk
3. The leftovers are mashed to turn the starches into sugar. This creates the liquid “wort”
4. The wort from the last step is then boiled and hops are added
   1. (This is where dissolved oxygen levels become important)
   2. DO < 0.05 ppm
5. Once complete, the solution is cooled, yeast is added and the fermentation process begins
6. Fermentation can range from 2 weeks to many months, allowing the yeast to turn sugar into ethanol and carbon dioxide
7. Optional: The fermented beer then enters a second fermentation to increase carbon dioxide and enhance clarification
8. The beer is packaged in bottles, cans, or kegs
9. The beer is enjoyed!

As you can see, step 4 when the wort starts to boil and the hops are added is a critical spot to start measuring in-line or sample measuring with a lab-grade dissolved oxygen meter. 

Why are dissolved oxygen meters important in the beer brewing process?

In the natural world, aquatic life relies heavily on enough oxygen to survive just like you and me. If dissolved oxygen levels drop too low there can be a large loss of fish and plant population. Therefore, dissolved oxygen measurements can provide a great insight into water quality, especially when paired with pH, temperature, and other probe measurements.

Conversely, in the beer brewing process, this relationship is almost the exact opposite. For the most efficient brewing process, water should contain almost zero dissolved oxygen to prevent contamination and oxidation during the brewing process, packaging, or after packaging. This contamination due to dissolved oxygen can lead to an old, musty beer taste and smell at a minimum and increase to worst-case scenarios where beer is undrinkable. Therefore, monitoring low dissolved oxygen levels with a DO meter is an extremely important step in the brewing process.

For context, in natural waterways, according to the Environmental Protection Agency (EPA), dissolved oxygen levels approaching 3 mg/L are in the danger zone for supporting common aquatic life, and that levels below 1 mg/L cannot support any aquatic life. On the other side, levels around 8-9 mg/L will support all life (fish or plants) and approach the oxygen saturation level of water.

On the opposite side, the brewing process requires a small amount of dissolved oxygen to fuel the yeast during fermentation, a very small amount. This dissolved oxygen level should be no greater than 0.05 mg/L or 0.05 parts per million throughout the brewing process.

Generally, dissolved oxygen will naturally balance itself in moving waterways full of fish and plant life. Since natural aeration, agitation will increase dissolved oxygen levels; but in a controlled brewing process DO levels should not increase or change drastically if all the equipment and aeration is working as planned. Reference this table for common dissolved oxygen levels in the brewing process.

For reference, three other factors affect dissolved oxygen including temperature, pressure, and salt concentration (salinity).

1. Temperature – as temperature rises, DO levels decrease
2. Pressure – as pressure decreases, DO levels decrease
3. Salinity – as the salt content increases, DO levels decrease

These 3 factors define the oxygen saturation level of a particular water system. In most cases, the dissolved oxygen level will not increase, naturally, beyond 13-14 mg/L but these three factors can be tweaked in the brewing process to create extremely low dissolved oxygen levels. 

As a result, proper monitoring of dissolved oxygen levels in the brewing process is extremely important to prevent over or under aeration (too much or too little dissolved oxygen). As a result, you’ll want to have an accurate and reliable dissolved oxygen meter. This particular kit from Atlas Scientific will provide everything you would need to measure and monitor dissolved oxygen. 

How do you measure dissolved oxygen in the beer brewing process?

Now that you understand the general process of brewing beer, the importance of dissolved oxygen in brewing beer, let’s take a closer look at actually measuring dissolved oxygen in the brewing process.

As stated above, the critical step to begin dissolved oxygen measurement and monitoring is where the wort starts to boil and hops are added (step four in this article). Additionally, on a lesser note, dissolved oxygen is inversely related to temperature so the boiling process will theoretically eliminate all the dissolved oxygen in the wort and brewing step. 

(Note: When taking DO measurements of the wort, ensure that all gases are in solution. Soluble gases such as oxygen are displaced by bubbles and other gases that will throw off the accuracy of dissolved oxygen measurements.)

Measuring dissolved oxygen in the beer brewing process can either be done in-line (direct, continuous measurements in the piping) or sampling at each step. In either case, a calibrated probe will be required to measure accurate levels of dissolved oxygen in the brewing process. Since the brewing process requires DO measurements and conditions below 1.0 mg/L, you will need to use zero dissolved oxygen calibration solution. Other brewers recommend using oxygen-free gas like ultra-pure nitrogen (pure CO₂ is usually not pure enough for calibration). However, when using oxygen-free gas for calibration it will require a more intense setup with calibrated air cylinders, air flow regulators, and so on to ensure the probe is only reading the oxygen-free gas. Either way, be sure to calibrate the DO probe to 0 ppm before measuring the brewing process.

This is a very important step. 

Do not skip calibrating the DO meter with a zero dissolved oxygen solution, otherwise the meter will not pick up the fine readings and small values of dissolved oxygen in the brewing process. Normally, the DO meters from Atlas Scientific will calibrate in air, but for this beer brewing case you will need to submerge the probe in a zero dissolved oxygen calibration solution, and then adjust the meter to read zero mV or zero mg/L. After this step, continue with one of the two measurement options: in-line or spot sampling.

Spot sampling of dissolved oxygen

For home brewers without a large setup or a new brewing operation, one will want to sample the wort with a calibrated dissolved oxygen probe (like the mini lab-grade DO probe) at various points along the process after boiling—to ensure dissolved oxygen levels stay below 0.05 ppm or 0.05 mg/L.

In-line measurement and monitoring of dissolved oxygen

Conversely, large brewing operations will want to consider in-line dissolved oxygen monitoring, via the industrial DO kit that attaches directly into piping, to spot issues quickly and reduce the time necessary to sample and measure dissolved oxygen. In this way, maintenance tasks and wasted product will be reduced with increased monitoring—to be preventative instead of reactive.

It is important to note if the pipes used for beer brewing are cleaned/exposed to normal air after each batch then you will need to recalibrate between batches. In this way, it is also a solid approach to spot measure with industrial processes, and keep a mobile DO measurement unit that stores the probe tip in an oxygen-free environment. 

Conclusion

Dissolved oxygen is an extremely important characteristic of water quality for any application (hydroponics, environmental sampling, fish farming, aquariums, brewing, etc) and especially for beer brewing (but in the opposite way as most other water applications. DO should exist in very small amounts, less than 0.05 ppm, to prevent unwanted contamination of the beer throughout the brewing process. However, a little bit is necessary to fuel the yeast in the fermenting process.

In this way, DO should always be monitored once the boiling process begins and the hops are added. Always keep a close eye on the dissolved oxygen levels of the wort throughout the brewing process. Be mindful of the conditions (temperature, pressure, salinity) and other natural factors that influence dissolved oxygen; but either way, these levels should stay low in a contained and validated brewing process. Overall, always use your calibrated dissolved oxygen meter to accurately measure and monitor dissolved oxygen to ensure that tasty brew does not go to waste.

If you would like to learn more about other water quality measurements, characteristics, or applications for dissolved oxygen, do not hesitate to reach out to the world-class team at Atlas Scientific.

Dissolved Oxygen Probes & Sensors