One of the best things you can do to promote yeast health is to provide plenty of oxygen at the start of fermentation. Oxygen is vital for yeast growth and development. But how much do you need, and how do you get there?
Professional brewers and yeast manufacturers recommend that oxygen be present in wort at a concentration of about 10 parts per million (ppm), a bit higher for lagers and high-gravity ales. The pros usually inject pure oxygen through a diffusion stone as chilled wort passes from the heat exchanger to the fermentation vessel.
As homebrewers, many of us don’t own a diffusion stone and a pure oxygen source, but you can achieve surprisingly high levels of dissolved oxygen with remarkably rudimentary techniques.
The yeast experts over at Wyeast Laboratories have experimented with various methods that homebrewers commonly use and measured the oxygen concentration using a dissolved oxygen meter. Here’s what they found:
- Allowing wort to spray into the fermentation vessel during siphoning achieves roughly 4 ppm.
- Vigorously shaking a carboy of wort for 40 seconds will get you up to 8 ppm.
- Injecting air into wort using an aquarium pump with a diffusion stone (see above) achieves 8 ppm in 5 minutes.
- Injecting pure oxygen into wort with a diffusion stone gets you to 12 ppm in 60 seconds.
So, if you routinely brew beers that can benefit from reliably high levels of oxygen (lagers and high gravity beers), then you may need a diffusion stone and pure oxygen to get you there. But if you mostly brew average strength ales, you can do just fine by shaking the carboy for a minute or so.