As a brewer, you already know the importance of controlling dO2 in your finished product. But did you know that it’s just as important to measure dO2 in wort? The right O2 balance – usually following your yeast manufacturer’s recommendations — will keep your yeast happy, so they don’t impart unwanted off-favors to your beer. However, if you’ve ever tried to measure the dO2 of wort using the same portable O2 analyzer you use for beer, then you know the challenge of minimizing flow chamber clogging from bits of trub and hops.
Years of dealing with this problem have lead to a simple solution, and it really works: run a sample of aerated or oxygenated wort (chilled!) from a sample valve into a small Erlenmeyer flask or beaker while holding a small probe from a hand-held analyzer in the flask. There are a few tricks, but for the most part this is a very straightforward way to get your measurements. Here are the main tracking points:
- Use an optical — also called Luminescent Dissolved Oxygen (LDO) – probe, so the flow rate of the sample can be low. Electrochemical probes require a fairly high flow rate.
- Run the wort from the sample valve and through a tube into the bottom of the flask. Use a flask with a reasonably narrow opening. Have the probe in the flask at the same time you are flowing your wort into the flask.
- It’s important to have flow into the beaker. It can be low, but put the outlet of the tube near the sensor, so the sensor responds well.
- Whenever possible, take your wort sample – the one you will use in the flask – from the process pipe before the yeast is pitched.
- Likewise, take the wort sample as far from the air or oxygenation point as possible.
- If you take your wort sample from the fermentation vessel, then you need to be on your toes, even taking the Erlenmeyer flask to the vessel so that you are measuring as close to real-time as possible. This is because yeast will quickly gobble oxygen, and that in turn can lead to significant underestimation of your starting oxygen value.
My final thought is that wort dO2 measurements can be as important as beer oxygen measurements. Keeping the yeast happy is your first step to creating a fantastic brew.