i don't have a stir plate and was wondering if it's beneficial to add O2 via canister to the starter? Currently, I swirl my gallon jug as much as possible.
Starters are specifically for increasing the yeast population density. Yeast reproduce in the presence of Oxygen and predominately produce CO2 and alcohol anaerobically. Shaking or swirling your starter (caution it will foam up) will introduce O2 into your wort.
Yes, excerpt from Mr. Malty: Q: Should I add oxygen to my starter? Yes. You'll get far healthier yeast and far more yeast growth if the yeast have oxygen throughout the process. Adding oxygen at the beginning helps, but the most effective starters provide a continuous source of oxygen. Oxygen is critical to yeast growth. Not providing any oxygen to the yeast can have a long-term negative impact on yeast health. Yeast use oxygen to synthesize unsaturated fatty acids and sterols, which are critical to creating a healthy cell membrane and good cell growth. With oxygen present, yeast convert sugar to carbon dioxide and water and they grow rapidly. With no oxygen, yeast create alcohol, grow far more slowly, and reach a lower total mass of cells. There are several ways to add oxygen: intermittent shaking, a stir plate, pure oxygen, or an air pump with a sterile filter. A stir plate is perhaps the most effective method. When using a stir plate, don't plug up the starter vessel with an airlock. A sanitary piece of aluminum foil or a breathable foam stopper is all you need. Bacteria and wild yeast can't crawl and a loose fitting cover will allow for better gas exchange. Shaking the starter as much as possible, every hour or two, makes a large difference in the amount of yeast growth and health. With enough attention and good air exchange, shaking is just about as effective as a stir plate. Continuous air from a pump and sterile filter can be effective too. The major drawbacks are being able to control the flow of air to prevent excessive foaming and evaporation of the starter. Shaking is just as effective as intermittent aeration with a pump. Continuous pure oxygen from a tank or oxygen generator is both expensive and unnecessary.
I used pure O2 to oxygenate my last starter, along with using a stir plate afterward for two days... Must have made some extremely healthy yeast as when decanted and pitched into my beer, fermentation took off in just a few hours with intense blowoff activity. I never had yeast work so quickly. Fermentation wrapped up in just three days and I could have probably kegged the beer after four or five days in primary. I will continue to use pure O2 for all future starters.
