[narvin]

I'm starting to question whether I need added aeration at all for ales.  I make large, aerated, stir plate starters, so I always end up with healthy yeast. For my Belgian beers, I think I get a better flavor profile when under-aerating (and still very high attenuation - 85 - 90% on beers with sugar).  I just made a Porter with WLP002, and other than splashing in the carboy, I did no aeration -- I didn't use my aquarium pump and stone. The result was great attenuation, a clean profile with just a hint of fruity esters, and less work.  I suppose I could get the same result with a smaller starter and aeration, but what's the point?

[mabrungard]

I am in the camp that aerates.  Even though you've created a population of healthy yeast with high sterols, they can still use more sterols as they acclimate and multiply in the lag and growth phases.  This is especially important with higher gravity worts. 

The good thing is that you indicate that you've made a large starter.  Have you compared that estimated yeast population to one of those pitching guides such as Mr. Malty?  If you're overpitching, then the need for aeration is reduced.  If you're only marginal, then aeration is still warranted. 

Remember that the effects of aeration only last about 30 minutes according to the new book on yeast.  The yeast consume oxygen very quickly according to that book.

[narvin]

I am in the camp that aerates.  Even though you've created a population of healthy yeast with high sterols, they can still use more sterols as they acclimate and multiply in the lag and growth phases.  This is especially important with higher gravity worts.  

The good thing is that you indicate that you've made a large starter.  Have you compared that estimated yeast population to one of those pitching guides such as Mr. Malty?  If you're overpitching, then the need for aeration is reduced.  If you're only marginal, then aeration is still warranted.  

Remember that the effects of aeration only last about 30 minutes according to the new book on yeast.  The yeast consume oxygen very quickly according to that book.

I definitely overpitched on the Porter by at least 10%, since it ended up being a lower gravity than I expected due to a mistake.  And although I'm usually pitching according to Mr. Malty for the Belgian ales, there are some breweries (Duvel, for example) that purposefully pitch below the standard ale rate of .75 million cells/ml/plato.  Going forward, I plan to use proper pitching rate and aeration for American or British ales, but I think I might keep experimenting with the pitching rate/aeration balance for Belgians.

[mabrungard]

Underpitching is also a good idea for Hefeweizens to enhance ester production.  I'm still thinking that aeration of a Hefe wort would be a good idea since the population needs to be built up.

[wingnut]

I have had similar thoughts... on the order of "just how much aeration do I need?" and "How easiest to do it?"  What I have pondered is just holding the drain line from my kettle about two or three feet over the fermenter and letting it splash in. 

My hypothesis is that more wort surface area will be exposed to the air and result in saturation of the wort very quickly.  To reduce the chance of dust/bacterial contamination on the first experiment, I thought about drilling a hole in the bottom of a brew bucket and inverting it over the fermenter... protecting the space from floating dust, but still exposing the wort to a large volume of air.

Anyone done/doing something similar?

[Kaiser]

Anyone done/doing something similar?

I recently posted results of an aeration experiment that used a perforated pipe: http://braukaiser.com/lifetype2/index.php?op=ViewArticle&articleId=140&blogId=1

In that experiment I only got to 4 ppm O2, which is about  50% of what you can get with air. The problem is that you need to be able to create lots of fine bubbles to ensure wort saturation with O2.

The oxygen need for fermentation has been the subject of many studies and while pro brewers will state that different yeasts have different O2 needs it is difficult for the home brewer to use this information. You would have to brew the same beer over and over and reuse the yeast from batch to batch to notice if the O2 you are giving the yeast is sufficient or not. For home brewers the O2 for the yeast comes from both the aeration in the starter and the aeration of the wort. Even with an oxygen meter that can measure the O2 in the wort it is difficult to assess the O2 that the yeast stored as sterols while growing in a starter.

Kai

[Kaiser]

One more point.

Narvin,
If you are interested in eliminating wort aeration for ales, go ahead and brew a side-by-side experiment. I think that it is possible if the yeast filled up with sterols in the starter. In addition to that the pitching rate should be high enough that yeast growth is limited to the amount that can be supported by those sterol reserves.

I.e. if the yeast sores 2x the sterols it needs for healthy cell walls, it can grow by 2x once until there will be a sterol deficit in the yeast cells. If it grows by 4x each cell only has ½ the sterols it needs for healthy cell walls. In wort fermentation the extent of yeast growth is largely limited by the available amino acids and sterol reserved. But we don’t want the latter to be the limiter since that means that the yeast has only marginal sterol reserves.

If you do this experiment you may also want to do the fast ferment test to see how close each of the test fermentation comes to the attenuation limit. This is also an indication of yeast health.

Kai

[euge]

I'm a splasher. And long questioned the need for extra efforts to aerate as long as a good healthy pitch is used. It does cross my brewer's mind every brew session though. Good thing this topic has been raised.

So thinking along... How about pitching a yeast-cake? To me that's over-pitching, but the need for aeration would be minimal. Or should the yeast be re-invigorated by using a portion of the cake to make a healthy starter?

[hopfenundmalz]

The yeast have different requirements, as Kai has stated.  The rules that I have read say that lager yeasts need a lot, as do flocculant yeast.  Powdery ones not so much.  There are also exceptions.

Sierra Nevada uses just filtered air.  Some of the Britiish brewers use a recirc. pump to spay the wort/beer through a fishtail nozzle back into the fermenter.  Some British brewers use(d) the double drop method to give the yeast more air well into the fermentation (about 16 hours). 

You could probably get by with minimal air for the first pitch, and then maybe see problems if you repitch many times.  I just go ahead and give the wort some O2.

[Kaiser]

So thinking along... How about pitching a yeast-cake? To me that's over-pitching, but the need for aeration would be minimal. Or should the yeast be re-invigorated by using a portion of the cake to make a healthy starter?

At the end of fermentation yeast has gown as much as it can grow. That what they do. And I’d assume that the sterol levels in each cell are fairly low. If you add this to fresh wort w/o aerating the yeast will still grow, since it has all it needs for that, but the sterol levels will get depleted even further. That may stop growth at some point and/or create yeast which has little tolerance towards alcohol. Either issue may cause flavor problems.

You also need to keep in mind that the level of yeast growth affects the flavor of the beer. You don’t want too much and you don’t want too little. Hence the idea of proper pitching rates. I do like refreshing yeast in a starter. One reason for that is that I noticed that the yeast performance quickly degrades during storage. I can tell the difference between yeast from a starter that has been dormant for 2 days vs. the same yeast having been dormant for 4 days. Maybe not in taste but in the time it takes the yeast to finish fermenting a batch of beer.

Sterols (i.e. aeration) and alcohol tolerance are closely related.  As he alcohol level increased the cell walls are under attack I think the alcohol leads to some sort of pitting. The yeast’s response to that stress is to increase the sterol content in the cell walls. This has been shown in laboratory experiments where the yeast actually had O2 available at the time of the alcohol stress.

But this is different in beer fermentations. When yeast is ready to bud it assess if it has enough sterols for itself and the daughter cell. At this point there is not much alcohol in the wort and the yeast doesn’t have to use a lot of sterols to reinforce its cells walls. So it may grow until each yeast cell has only the bare minimum of sterols left. But later, as the alcohol increases, it would like to make stronger walls but can’t and eventually may be forced to give up on fermenting even before all the sugars are consumed -> stalled fermentation. This is how I see the problem of higher gravity fermentation, pitching rate and need for aeration. Fill the yeast cells will sterols during yeast propagation, add an adequate amount of O2 to the wort and pitch more yeast than usual so the individual cells don’t have to bud and share split their sterol reserves so often.

Kai

[wingnut]

I recently posted results of an aeration experiment that used a perforated pipe: http://braukaiser.com/lifetype2/index.php?op=ViewArticle&articleId=140&blogId=1

In that experiment I only got to 4 ppm O2, which is about  50% of what you can get with air. The problem is that you need to be able to create lots of fine bubbles to ensure wort saturation with O2.

Thanks Kai!

Gotta love hard data and I really appreciate you posting your experiments!

[oscarvan]

It so happens there's an oxy-acetylene set in the brew house......so I just got a stone and hook it up to the O2 bottle.....many tiny bubbles for a few minutes. No hard science, but good fermentation.

[majorvices]

Just to add to everything Kai has said, the yeast are what needs the air - not the wort. If you can be sure the yeast has been aerated (and, hence, the sterol reserves built up properly such as on a stir plate) you shouldn't need to aerate the wort. However, aerating the wort is the easiest way for most brewers to get the o2 to the yeast. That said, I have heard of a few breweries that aerated only the starter and not the wort.

[Kaiser]

I wonder how much o2 the yeast actually gets on a stir plate. I say that only because I have seen increased fermentation performance from yeast that has been grown with continous aeration.

Kai

[majorvices]

I say that only because I have seen increased fermentation performance from yeast that has been grown with continous aeration.

Me too. In fact I grow almost all my yeast now under constant aeration. I've also wondered about how much aeration the yeast get on a stirplate. Don't you have a DO meter? You should test it. Though I assume it would be hard to measure once the yeast start creating Co2.