By Chris Jennings
For the Oregon Beer Growler
The process of fermentation is a wondrous one. As brewers, we only have so much control over the outcome of a batch. Much of the work is done by yeast, and we simply strive to create an environment for that yeast to flourish. Besides adding a bunch of sugar for the yeast to metabolize, there is another ingredient that’s often overlooked on the homebrew level: oxygen. Yes, oxygen is bad in a finished beer, giving it a cardboard-like flavor. However, it’s crucial for the beginning of fermentation. Having the right amount of oxygen dissolved in your wort is going to noticeably affect the completed brew. The yeast will reproduce better, fermentation will be faster and the finished beer will be cleaner.
Now that you know that oxygen is beneficial, how do you get it into solution? The easiest and least invasive way to get oxygen into the wort is to either shake your fermenting vessel (not recommended with glass carboys) or by allowing the wort to splash as it flows into the fermenter. These methods are easy and cheap and it’s also next to impossible to get too much oxygen into the fermenter.
Another method involves an oxygen tank (available at some hardware stores) and a diffusion stone (available at most homebrew supply shops). The stone should be connected to a hose that comes off of the regulator on the oxygen tank. When the tank is opened, the tiny holes in the stone force oxygen into the batch. With a pure gas supply, there is the risk of over-oxygenating. If this happens, fermentation will be rapid but the yeast can stall and fail to clean up off flavors such as diacetyl and acetaldehyde — presenting the unwanted essence of buttery popcorn or green apple.
The amount of dissolved oxygen needed is approximately 1 part per million (ppm) for every degree plato. For instance, if you have a beer with a starting gravity of 1.065, your plato is 15.9, so you would need just under 16 ppm of oxygen. There are a handful of ways to measure dissolved oxygen in a solution. The most expensive method is a handheld electronic meter, which comes with a probe that’s inserted into the wort in order to extract oxygen and provide a reading. Unfortunately, this also removes oxygen from the batch, so if you try to obtain another reading from the same spot, the number will be lower.
Another, less-expensive option for measuring is a colorimetric test. This can be found at most aquarium supply stores and works like a chlorine test for a swimming pool. Simply add some wort to a vial, dilute it with water and then add a chemical that will turn the solution a different color (usually blue). Compare this shade to the provided chart and you’ll have a measurement. Of course, this won’t work well on dark beers.
The least-expensive way to measure is simply to experiment, which is what homebrewing is all about anyway! Start by adding small amounts of oxygen with each batch until you notice an improvement in your beer. Record the length of time you allowed the oxygen to bubble or how long you shook your fermenter and then make that a common practice. Once you’re in the right range, you’ll only need to take readings every couple of batches to ensure you’re still on track.
Nasal Blaster [AG]
Nasal Blaster [Extract]
Stories from the print edition of the Oregon Beer Growler.