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I have a Dunkelweizen from a Northern Brewer all-grain kit that I brewed and pitched 2 weeks ago. I have one problem, I forgot to aerate before I pitched the yeast. I'm concerned that the yeast will not have enough oxygen to carbonate when I bottle it. I have more yeast I can pitch when I prime(Wyeast 3068), but will that be enough? Will aerating it now give it a bad taste? Any advice would be appreciated!

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a side note: I wouldn't add yeast right before you bottle youtu.be/Kuv8F4uORA8 or youtu.be/4cf10vcFCck –  Ryan Shdo Nov 30 '11 at 4:27
    
As a side note, separate aeration is all well and good, but not 100% necessary. On your next batch, before pitching the yeast, just shake the carboy really good once the wort is cooled down. This will introduce enough oxygen to make a good beer. –  Graham Dec 13 '11 at 13:36

3 Answers 3

The carbonation process occurs due to fermentation of the priming sugar. Fermentation is an anaerobic process, therefore no additional O2 is needed for carbonation to happen. You'll pick some up anyway through simply by racking.

Excess O2 post fermentation will oxidize the beer and create stale flavors as well.

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+1 Prompted more reading: "When oxygen is present, the sugar molecules are broken down into carbon dioxide and water (plus energy that the yeast uses to grow and reproduce). In the absence of oxygen, the sugar molecules are not broken down completely. The end products are alcohol (with two carbon atoms) carbon dioxide (one carbon atom), and water. Less energy is extracted from each sugar molecule: the energy that could be extracted from the alcohol molecule if oxygen were present." Which explains why we want O2 at first: the yeast are more energetic and will reproduce more happily. –  JoeFish Nov 30 '11 at 14:33
    
Link for above quote: sciencebuddies.org/science-fair-projects/project_ideas/… –  JoeFish Nov 30 '11 at 14:34

If the beer has been fermenting leave it be and if you pitch more yeast to save the beer then use a champagne yeast or safe ale 05 but don't aerate it will make matters worse like everyone else has said.

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this wasn't my downvote, but it seems you may have mistaken the question. Your answer is a better fit to saving a stuck ferment, while the question is about bottle priming, and if aeration is needed there. –  mdma Dec 23 '11 at 0:11

You should only aerate before the yeast have had a chance to really get going, so that they can consume all of the oxygen that's in suspension. It's really too late now, and will likely result in oxidized flavors. The yeast should be fine for carbonating your beer with simply the priming sugar, though.

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I'm not sure baka said it strongly enough: DO NOT AERATE BEFORE BOTTLING. Your yeast would have benefited from the aeration in the early stages of fermentation, when they are multiplying, as this is an aerobic process. Now that fermentation is complete, the only thing this will do is greatly accelerate staling. –  Dustin Rasener Nov 29 '11 at 23:19

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