Oxygen requirements for Fermentation

During fermentation, yeast has a couple of choices. If it has oxygen available to it, it will be able to reproduce quite rapidly (doubling every 3 hours). If there is only limited oxygen available, it will turn its task to producing ethanol and other products (about 1300 in all), like higher alcohols (sometimes called fusel oils), esters, organic acids, and carbonyl compounds. To get good initial growth of the yeasts, you want to have a bit of oxygen available - but you can do this simply by stirring the wash vigorously when disolving the sugar. Once you have added the yeast, it is critical to seal the container such that air cant get in, but you can still let the CO2 out, by using an airlock. To minimise the amount of other volitiles produced, make sure that you are using a yeast designed for the job, and keeping it happy with nutrients & with a stable temperature.

Fizz writes ..
    ..for those of us who have heard about the need for oxygenating the water prior to pitching the yeast and (like me) cannot afford extra equipment to do this I would recommend (if you have one) a kitchen stick blender, like what you use to make soups or sauces etc. 2 minutes in that baby and the water had that much O2 in it, it turned milky !
If you're going to use an airstone to aerate the wash, Mecakyrios recommends ..
    1.) I HIGHLY recommend for you to use an in-line HEPA air filter. This will allow for the air going through it to be essentially sterile when it comes out through the air stone. This aids in protecting your wash from becoming infected with unwanted nasties.

    2.) I would recommend using a racking cane with a small piece of tubing connected to your air stone. Let me try to explain better: You have you air pump connected to the correct length of tubing to get to your wash. You connect that tubing to your racking cane. To the other end of the raking cane you add a small piece of tubing, and to that tubing you put on your air stone. Then you submerge the air stone by placing the raking cane into the wash. What this will do for you is allow you to position the air stone where ever you may need to, but more importantly it will keep the stone from floating to the top of the wash. By using the raking cane (or similar device) method you now have more control over the air stone while making sure that it remains submerged.

    There are brew shops that sell both of these products. Some even sell special "air wands" that come with both the filter and a special "wand" that keeps the air stone submerged.

    If you would like more information, or at least a look at some products for this topic, I would recommend going to http://www.williamsbrewing.com/. Go to the fermenting equipment section and then go to "Wort Aeration" section to look at some products that deal with this issue.
Ted Palmer writes ..
    In order to properly "grow up" a series of yeast starters you must aerate the wash with sterile air or pressurized oxygen (O2). The reason for this is that yeast cells bud or reproduce only when there is enough oxygen present to grow. During fermentation yeast cells will still bud, but at a slower rate since it has to pull oxygen out of chemicals. The amount of O2 required is small, on the order of 20 microliters per ml. to support the budding phase.

    So how do you put O2 in your wash?

    Sterile air:
      Pump air through a 0.02 micron filter and then a stone (fish tank bubblers work well) into the wash. If you can't get a filter use a jar setup like a thump barrel only put a stone on the inlet pipe, fill this with hydrogen peroxide halfway full. pump air through this jar and then a stone into the wash. Run this setup 20 - 30 seconds for each liter of wash.

    Pressurized O2:
      Use any tank of pure oxygen fitted to a stone on a length of tubing, run for 5 - 10 seconds for each liter of wash.
    Aerating a fermenting wash will result in one hell of a lot of yeast and very little alcohol. Aerating a fermenting wash for even a short time will oxidize flavor components including ethanol !!!


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