Wort Oxygenation & Aeration
In the presence of oxygen yeast are able create certain materials (sterols & unsaturated fatty acids) they need grow and create healthy cell walls. Healthy cell walls mean healthy yeast. When yeast are healthy, yeast ferment strongly and have shorter delays before the start of fermentation. Healthy yeast are also better able to handle the stresses of high SG / final alcohol beers (> 1.065 SG) and as a result will create less sulfur compounds and attentuate reliably. In short, healthy yeast make better beers!
Understanding the Need To Add Oxygen:
The most important time for oxygen to be in the wort is when the yeast first go into the wort (inoculation) and begin the growth phase. However, when we boil the wort, it effectively removes most of the oxygen from the liquid. If there is to be oxygen in the wort, then we must add it ourselves.
How Much Oxygen Is Needed & How do I Add It?:
While most yeast strains have individual oxygen requirements, the average amount needed for a healthy fermentation (SG < 1.065) is between 7 to 18 ppm (around 10 ppm). There are two ways to introduce oxygen into wort, Shaking/Agitation/Splashing and forcing gas through a Stainless Steel Diffusion Stone. Each method delivers a certain amount of oxygen:
- Shaking/Agitation/Splashing for 40 seconds = 8 ppm max
- Aquarium pump with a diffusion stone for 5 min (using air, which is 20.8 % oxygen) = 8 ppm max
- Pure oxygen in a pressurized tank with a diffusion stone for 60 seconds = 0-26 ppm
Note: The most effective method is the pressurized tank, but it is also the most expensive. If you are doing standard gravity beers (SG < 1.065) any of the above methods should supply the necessary oxygen. However, keep in mind that wort with a SG > 1.065 requires higher starting oxygen levels to keep yeast healthy, and at higher sugar levels oxygen solubility actually decreases. So, if you are doing higher gravity beers, a pressurized gas set-up is really the only way to get enough oxygen into your wort.
Some Useful Information When Oxygenating:
- Only add oxygen to wort when inoculating at the beginning of fermentation. (Adding it later will oxydize the beer.)
- Only add oxygen to cooled wort (< 80 F). Adding oxygen to hot wort creates off flavors (Hot Side Aeration) and can darken the color.
- Yeast use all availible oxygen in the first 3-9 hours. As long as you are doing a 1 or 2 time dose and are not running pure oxygen on a continuous basis, there is no real danger of over-oxygenating, only under-oxygenating.