Pitching on the cake + aeration

So I'm thinking there's no burning need to aerate a wort that is pitched onto a yeast cake. My understanding is that the purpose of aeration is to supply oxygen that yeast need during reproduction / population growth, and that once fermentation begins the little beasties need no more oxygen. Since a cake is "mostly" viable yeast, it shouldn't reproduce much and therefore wort pitched on a cake shouldn't need aerated.

Am I off base here?

Except that you'll miss out on the growth phase of the yeast and the flavors/esters that imparts.

Mr. Malty has a pitch calculator for the amount of slurry you would need to pitch so that you don't "overpitch."

I dont aerate when I pitch onto a cake.

On second thought, I dont aerate anything at all, I dont have a stone or whatever, so I am no help.

mmb said:

Except that you'll miss out on the growth phase of the yeast and the flavors/esters that imparts.

Mr. Malty has a pitch calculator for the amount of slurry you would need to pitch so that you don't "overpitch."

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I realize that Mr. Malty has a calculator. My question was simply about aeration. Seems to me that there are a few beers out there that might benefit from a quick, esterless fermentation.

I plan to try out a small split batch- pitch one to spec, and pitch the other with the entire rest of a cake.

With any beer where you would use Nottingham, US-05, US-04, 1056, or any other "clean" flavor profile just pitch on the cake, no aeration needed. Fermentation will be done in 2-3 days and as long as you control the profile it will finish out clean and ferment out completely. My last pale ale I pitched onto a cake of 1056 and it blew off 4 hours after I pitched...crazy stuff!

Pouring the wort into the fermenter with a yeast cake should be any/all aeration needed when using a cake or a lot of slurry.

it boggles my mind that anybody would want to pitch onto a yeast cake.

RBlagojevich said:

it boggles my mind that anybody would want to pitch onto a yeast cake.

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Why not? There's plenty to recommend it- it's a guaranteed, fast-starting fermentation that hits FG quickly.

RBlagojevich said:

it boggles my mind that anybody would want to pitch onto a yeast cake.

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Please explain. I consider a yeast cake a 5 gallon starter.

+1 to the goodness of the yeast cake.
I won't usually do it if I have to keep the cake longer than overnight, but if I bottle/rack one night and know I am planning a brew the next day, I will always try and pitch on the yeast cake. It is a HUGE starter, and I hear that is good, plus you save either the $6 for liquid yeast or $2 for dry. I can understand some of the ultra snob brewers will not want the possible autolysis, leftover trub, or hop residue but I have never had a bad brew from a cake pitch, just doesn't happen. Hell, I have cross pitched before, putting a cider on top of a beer cake. Grow a pair and try some stuff!

RBlagojevich said:

it boggles my mind that anybody would want to pitch onto a yeast cake.

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Have you read any of Jamil's recipes? Some of them call for starters > 2L...that's a LOT of yeast. I think I remember seeing one that was 7L. And most commercial breweries aim to have fermentation over in 3-4 days MAX. Fast fermentation means less chance for infection, lower power bill, and quicker to market.

I pretty much always pitch onto the cake or if it's going to be more than a day, I pour the cake into mason jars and pitch on that. I usually don't even wash the yeast if I'm going to use it in a week or two. Never had a problem yet, the beers ferment out in a couple days, and always taste great. I've kegged hefes within a week that way.

As TwoHeadsBrewing and the original post pointed out, pitching onto a yeast cake is going to be overpitching for most beer styles, but for those where you want a clean fermentative character that is caused by little yeast growth, it might produce nice effects.

The second question concerns oxygenation. In my opinion, I would slightly aerate the wort that is pitched onto the top of the yeast cake. As malkore noted, the process of simply pouring the wort into the carboy may provide enough aeration in this situation. But the reason why this is the case is interesting. Highly aerating it would be a problem, because a large amount of the sugars in the new wort would be utlized for aerobic yeast growth (increase in biomass) rather than for fermentation (production of ethanol), due to the huge amount of yeast available.

The yeast in a yeast cake are going to have substantially exhausted their reserves of lipids (sterols and unsaturated fatty acids), which are built up in an aerobic environment. If unaerated wort is pitched onto yeast in such a state, there is the possibility that an unsuccessful fermentation is going to occur, because these reserves of lipids are required to support cell metabolism. "Failure to provide sufficient oxygen is one of the prime causes of slow and sticking fermenations" (Brewing: Science and Practice). However, given the huge yeast count in a yeast cake, the cells do not have to build up a large supply of reserves in order to completely ferment the fresh wort poured on top of them, because the wort would probably be completely fermented after only 1 or two cell doublings. Therefore, the limited amount of aeration provided by pouring the wort on the yeast cake MIGHT be sufficient to bring fermentation to completion. But, rather than risk it, I would moderately aerate the wort. Both over-aerating and under-aerating can both cause you to miss your target final gravity, but under-aerating will also mean under-attenuation. Over-aerating will mean more of the sugars were used for the production of cell biomass, CO2 and water instead of ethanol, so it is probably better to err on this side.

Anyway, to finally answer the original question -- yes, you do not need any more yeast growth, but the yeast do need lipid reserves in order for fermentation to progress. So although you have enough yeast in the yeast cake, the nutritional requirements of those yeast are not fulfilled by simply providing them with unaerated wort, and so you are risking the possibility of a stuck fermentation. The large amount of yeast reduces this risk, but the results are unpredictable because there is not a good way to know exactly how much aeration to provide to such a large amount of yeast.

mmb said:

Except that you'll miss out on the growth phase of the yeast and the flavors/esters that imparts.

Mr. Malty has a pitch calculator for the amount of slurry you would need to pitch so that you don't "overpitch."

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So, when you are using a yeast cake, you are really just supposed to use a piece of the cake? So, am I an idiot for using the entire cake?

Confusing terminology.

I only pitch on a yeast cake when the new wort is 1.100 or close to that. It has worked great so far in getting good attenuation. I don't shake it to aerate, but I'm sure it wouldn't hurt if you did.

Edit: I don't do Belgians, on those you would want the growth phase of the yeast so probably only pitch part of a cake even at high gravity.

I just used washed yeast on friday when I brewed an Arrogant Bastard clone. I washed the yeast the night before from my APA and put it in three jars. I wasn't making a starter and I got a pretty thin layer of yeast in my jars so I went ahead and used two jars in the AB brew. I aerated and had about a 12 hour lag time but it was krausen city after that.

kniles38 said:

So, when you are using a yeast cake, you are really just supposed to use a piece of the cake? So, am I an idiot for using the entire cake?

Confusing terminology.

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When people say "pitching on a yeast cake," they mean they whole thing. Plenty of people do it and undoubtedly make great beer.

The fact of the matter is that the recommended pitching rate for ales is 0.75 million cells per milliliter per degree plato (double that for lagers). This is what the experts (Wyeast, etc.) say. If you call that the "correct" pitching rate then pitching onto an entire cake, in most cases, is over pitching. Just as pitching one tube or smack pack is under pitching. IMO, this is not the debated part.

The debate lies, however, in whether over pitching makes a noticeable difference. Yeast make unique flavors during the growth phase, if you pitch essentially enough yeast where no growth occurs you will not get those flavors at that point. Now the question comes up: "Does that matter?" I think this is the point people debate. It is entirely possible that the flavors that a yeast makes during the rest of fermentation make detection of the earlier flavors impossible or that other parts of the beer cover them up (hops, roast, etc.).

Someone really needs to do some side-by-side experiments. Ferment out a batch, harvest all the yeast, use the Mr.Malty calculator (or better yet a microscope) to determine the "correct" amount of yeast to pitch. Pitch the "correct" amount in a subsequent batch and double (or triple) that in another. Ferment the beers out noting lag and and time to FG. Then, most importantly, do some triangle tests and see if people can detect the difference and if either is preferred. I would suspect that people would be able to detect a difference and have a strong preference only in certain styles (not hoppy ones, etc.).

dwarven_stout said:

Why not? There's plenty to recommend it- it's a guaranteed, fast-starting fermentation that hits FG quickly.

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I would (and many others) argue that if you pitch the proper amount of healthy yeast (0.75mil/ml/degPalto) you will get a fast-starting fermentation that hits FG quickly. (This has been my experience). More yeast is simply not necessary for this to happen.

TwoHeadsBrewing said:

Have you read any of Jamil's recipes? Some of them call for starters > 2L...that's a LOT of yeast. I think I remember seeing one that was 7L. And most commercial breweries aim to have fermentation over in 3-4 days MAX. Fast fermentation means less chance for infection, lower power bill, and quicker to market.

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But all of those starter sizes are based on 0.75million yeast/ml/degPlato (double that for lagers) in a simple starter from one pack/tube. Some big beers do require a lot of yeast/big starters. I think Jamil would even agree that making starters this big is way too much work and pitching from a previous batch is easier. I would also argue that commercial breweries that re-pitch are not over pitching, they harvest the yeast and split it up or pitch into a larger batch. I have never heard of brewery repitching the entire yeast load from one batch to another.

If the cake is cali ale or something I use a lot of and I'm ready to pitch a new wort when I happen to be racking out a previous batch, I collect a one quart slurry first and pitch on what remains. That's still at least the same yeast amount as a 2 liter starter, probably much more. Yes, I still apply 60 seconds of pure O2, just like any other batch. It's more about yeast health than trying to build up more cells.

I've brewed a number of beers pitching directly onto the cake, and have been happy with the results.
For clean, simple ales, it's sheer laziness and thrift, not having to clean out the fermenter and saving $2 on dry yeast.
For brewing heavier lagers, I've done it to avoid having to make huge starters with multiple yeast packs.
I also enjoy the medieval aspect of it

So with the argument that the yeast need to build up their lipid reserves, does that mean that the much talked about and debated practice of adding olive oil to the fermentation would account for the needed lipids in order to make the yeast more healthy? Possibly add a bit of oil to the cake and pitch on top to avoid the lipid reserve issues brought up by stoutaholic?

Someone in the audience asked about olive oil at the troubleshooting panel with Vinnie Cirulzo, John Palmer, Ken Grossman and others and they all basically said, give it a shot but we already have enough head retention concerns without adding more oil.

Beerrific said:

Someone really needs to do some side-by-side experiments. Ferment out a batch, harvest all the yeast, use the Mr.Malty calculator (or better yet a microscope) to determine the "correct" amount of yeast to pitch. Pitch the "correct" amount in a subsequent batch and double (or triple) that in another. Ferment the beers out noting lag and and time to FG. Then, most importantly, do some triangle tests and see if people can detect the difference and if either is preferred. I would suspect that people would be able to detect a difference and have a strong preference only in certain styles (not hoppy ones, etc.).

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I definitely plan to do this at some point.

I actually suspect that hoppy and bitter beers, as well as belgians, would be the ones that you don'twant to massively overpitch- belgians because you'd miss out on yeast character, and higher IBU or hoppy beers because you'd lose a lot of hop characteristics out the top with the blowoff (IIRC, Ray Daniels cites a source in Designing Great Beers that claimed excessive blowoff can translate into a loss of up to 40% calculated IBU).

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