Instructions for making starters include using a stir plate for several hours to introduce oxygen into the starter wort. Are there any issues with using pure oxygen and a wand/stone to inject oxygen in lieu of the stir plate to save time?
Joined: 12 Dec 2010 Posts: 10058 Location: Ottawa, Canada
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Link Posted: Mon Mar 11, 2019 12:14 pm Post subject:
Most instructions for making starters will tell you to use a stir plate until fermentation is completely done - that's typically a day or two, or possibly longer depending on the age of the yeast (older yeast will take longer to build up and finish). Really fresh yeast may be done within 12-24 hours, I've had packs that are 6-12+ months take 3-5 days.
The constant stirring introduced by a stir plate helps speed up fermentation and also introduces atmosphere which has the O2 that the yeast needs.
Starters are typically low gravity (around 1.030-1.040) so using pure oxygen isn't required to get to optimal O2 levels for maximum yeast growth. Seems like overkill and would be hard to regulate the slow constant addition of O2 over a day or two not to mention that at the rate you'd be introducing O2 it wouldn't be stirred, so I don't see how it would speed things up. With constant pure O2 addition it may also be possible to over oxygenate which may have other consequences.
Using pure O2 (or even an aquarium pump) would also cause the wort to foam a lot. You'd need a much larger container or flask to avoid it bubbling over (just like when you aerate 'regular' wort with pure O2 or an aquarium pump - it tends to foam up a lot).
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.
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