Oatmeal Stout Aeration

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Oatmeal Stout Aeration

Postby jam_phan » Tue Nov 20, 2007 2:22 pm

I am thinking of making an Oatmeal Stout this weekend and the recipes I have been finding are calling for 15 minutes of aeration using a air pump. Is this really necessary? I do not want to have to buy additional equipment before I brew this weekend. Is there an alternative to using an air pump?
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Re: Oatmeal Stout Aeration

Postby billvelek » Tue Nov 20, 2007 3:04 pm

jam_phan wrote:I am thinking of making an Oatmeal Stout this weekend and the recipes I have been finding are calling for 15 minutes of aeration using a air pump. Is this really necessary? I do not want to have to buy additional equipment before I brew this weekend. Is there an alternative to using an air pump?
Most brewers do NOT use an airstone and air pump, so you should be able to find plenty of recipes which do not specify that; in any event, you can make the same recipes and skip the pump aeration. There are a number of other ways to aerate your wort, and, in fact, aeration isn't even necessary if you pitch a yeast starter that is large enough and healthy enough. I wish I had more time to explain, but will have to come back to this later; meanwhile, just understand that there is nothing special about an "oatmeal" stout that requires any particular type of aeration.

Cheers.

Bill Velek
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Postby jam_phan » Tue Nov 20, 2007 3:28 pm

"there is nothing special about an "oatmeal" stout that requires any particular type of aeration"

That is the line I was hoping to read. I will plan on brewing as I normally do, pitch the yeast starter and stir like hell!

I am interested in hearing your explanation though, for education reasons.
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Aeration not necessary if yeast count is sufficient

Postby billvelek » Tue Nov 20, 2007 8:25 pm

jam_phan wrote:I am interested in hearing your explanation though, for education reasons.

Okay, you asked for it. :mrgreen: Seriously, I am no expert but this is my understanding based on a lot of reading and many years of brewing.

First, the _only_ purpose for aerating wort (or a starter) is to improve the yeast count and their condition -- the total population of yeast and perhaps their overall health. too. This is because oxygen is an essential constituent of some substances that a yeast cell needs in order to live, grow, and 'bud' another yeast cell (reproduce). Yeast are capable of living in an environment (wort) which either HAS or does NOT have oxygen readily available, and their metabolic processes switch accordingly; when oxygen IS available (aerobic phase), the yeast will produce _some_ ethanol (crabtree effect) but will primarily devote their energy to growth and reproduction. On the other hand, when oxygen is NOT sufficiently available (anaerobic phase), the yeast will STOP reproduction (impossible to reproduce without the necessary building blocks) and will instead merely survive for awhile producing ethanol as a waste product in the process.

What we want to do is convert a given mass of fermentables into the waste product as quickly and efficiently as possible, and there are two ways to do that: either start with a population that is large and healthy enough -- in which case you really don't want reproduction because that would just waste energy -- or you can start with an inadequate population and provide it with what it needs (oxygen being one thing) to reproduce new yeast cells to make up the difference. So, the bottom line is that by making an adequate yeast starter, there is absolutely no need to aerate, and in fact aeration would be not only a waste of time, but also a waste of fermentables (creating unnecessary yeast cells instead of ethanol).

Personally, I don't aerate my worts other than what happens accidentally, because it is a pain in the !@# waiting for the foam to subside to continue filling the carboy.

I don't want to make this any longer than necessary because most folks probably won't read it all anyway. You can find more info at http://www.mrmalty.com including a "Yeast Pitching Rate Calculator" here: http://www.mrmalty.com/calc/calc.html which will tell you all that you need.

By the way, yeast need food (sugar), oxygen, and various minerals and whatnot that forms their cells. You can buy yeast nutrients and yeast energizers to help promote yeast growth in your starter, and I use those products, but I always give my starter solution a very healthy dose of boiled baker's yeast. That's right; I go to Sam's or wherever, and I buy a bulk package of baker's yeast, and when I boil my starter solution, I add a good tablespoon or so of baker's yeast. Those yeast cells rupture during boiling, releasing exactly the minerals that those cells need, and newly developing BREWER'S yeast cells consume whatever they need of that stuff while they reproduce. It's cheap, and I always get a great start without any off flavor's from the baker's yeast that I've ever detected. Just a tip that I picked up from other brewers some years ago.

Cheers.

Bill Velek
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Aeration

Postby brewmeisterintng » Tue Nov 20, 2007 8:32 pm

The simple explanation is that yeast need 02 to multiply. If you have an adequate pitch of yeast, it will do what it is suppose to. Back when I first started brewing I pitched a vile or packet of yeast and though I was good to go. The truth is that I was under pitching my yeast and was expecting the shaking of the carboy to introduce enough O2 for the yeast to multiply and ferment the wort. I have since learned the value of a good yeast starter. I have just built a stir plate as that seems the logical course to ensure that I have an ad equate source of viable yeast.:D
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