Repitching on cake - overpitching risk overstated?

Hi all,

I've read quite a bit online about the virtues of repitching wort on top of a used yeast cake, and one concern that always comes up is the risk of overpitching the yeast.

I've read quite a few accounts of people who just pitch on top of the old cake time after time with fantastic results, and just as many accounts of people who take great pains to collect the spent cake, wash it, and then repitch just a portion of the harvested yeast to avoid overpitching.

What I haven't seen anywhere are people who have just repitched on top of the old cake and had off flavors or other problems associated with overpitching. So I'm wondering if people who worry about overpitching are being overly cautious? Has anyone ever had a problem with too much yeast in their beer due to repitching?

Thanks,

TD

There are several potential problems associated with massive overpitching:

1) Formation of off-flavors.
2) Lowered ester production. Good for (most) lagers, bad for ales, and especially bad for most wheat beers.
3) Loss of hop bitterness. The extremely vigorous fermentation you get from dumping on a cake can push a lot more hop compounds out the blowoff than normal, dropping your IBUs.

All that said, I've pitched on a cake a couple of times and noticed nothing majorly off, and the practice does have its merits (who doesn't like having a beer done in 2 days, anyway?).

It really depends on what you're brewing. I'd never pitch a Belgian or wheat on a prior yeast cake as there wouldn't be enough yeast growth to produce all the desirable esters and phenolics. For a clean ales or especially lagers, I like to pitch back-to-back batches on the cake two or three times. It really does produce a cleaner beer.

I wash my yeast to get rid of as much of the non-living yeast debris as possible in the cake. There is a huge amount of dead yeast cells, precipitated proteins, hop refuse, etc in that cake that will, at some point, start to contribute less than desirable additions to the flavor of the beer.

Would I lose sleep over these possible off flavors if I pitched directly, no. But still, at some point that debris is going to degrade to the point where it starts emitting noticable levels of off flavors. I would prefer not to have a beer on it when that happens.

The reason I would pitch on a lesser amount of yeast than is in the cake is the lowered esters. This especially for Belgians where the yeast provides so much of the flavor profile. And yes, I can taste a flatter profile in an overpitched Belgian.

I find it doesn't take more than a minuet to swirl up the yeast cake and dump it into a measuring vessel. When you overpitch at that extreme of a level the yeast will use up the nutrient and oxygen stores far too quickly. This will lower the vitality of the yeast and you also won't get much reproduction, which will substantially reduce many of the flavors we associate with beer.

You also will have no idea how much yeast you pitched, making it impossible to reproduce.

dontman said:

I wash my yeast to get rid of as much of the non-living yeast debris as possible in the cake. There is a huge amount of dead yeast cells, precipitated proteins, hop refuse, etc in that cake that will, at some point, start to contribute less than desirable additions to the flavor of the beer.

Would I lose sleep over these possible off flavors if I pitched directly, no. But still, at some point that debris is going to degrade to the point where it starts emitting noticable levels of off flavors. I would prefer not to have a beer on it when that happens.

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Thanks for your input!

I understand the principle that at some point the trub will have a detectable effect on the beer, just like overpitched yeast can have an effect. What I'm trying to find is someone who has taken it too far and can tell us where that line is.

TD

I'll pitch on a cake once, then I pour off most of the trub for successive batches. I've never had off-flavors, but trub build-up can be annoying.

jkarp said:

It really depends on what you're brewing. I'd never pitch a Belgian or wheat on a prior yeast cake as there wouldn't be enough yeast growth to produce all the desirable esters and phenolics. For a clean ales or especially lagers, I like to pitch back-to-back batches on the cake two or three times. It really does produce a cleaner beer.

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Tonedef131 said:

I find it doesn't take more than a minuet to swirl up the yeast cake and dump it into a measuring vessel. When you overpitch at that extreme of a level the yeast will use up the nutrient and oxygen stores far too quickly. This will lower the vitality of the yeast and you also won't get much reproduction, which will substantially reduce many of the flavors we associate with beer.

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Thanks for the advice!

So I see that one problem with repitching on a yeast cake is that beers that depend on the byproducts of yeast growth, like Belgians or Hefes, will not develop the desired flavor profile.

There are whole classes of beers that don't depend on the yeast to provide flavor to the beer; what about those?

Has anyone ever pitched on top of a used yeast cake and later said 'Damn! I wish I hadn't done that!' What happened with that beer?

TD

I've done it a dozen times or so and I've never had an issue. We hear about overpitching but when has anyone here ever come back and said they had off flavors because of it?

I'm not saying it's not possible but I think it falls in the category of HSA or autolysis; it can in theory happen but it's rarely does.

Nurmey said:

I've done it a dozen times or so and I've never had an issue. We hear about overpitching but when has anyone here ever come back and said they had off flavors because of it?

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That's exactly why I started this thread; I'm hoping to hear from people who've had the problems that are usually only mentioned theoretically.

Nurmey said:

I'm not saying it's not possible but I think it falls in the category of HSA or autolysis; it can in theory happen but it's rarely does.

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That's what I suspect may be happening, so I thought I'd get that conversation started to see if we can get anywhere.

What do you think of the point that it'll have a negative effect on beers like Belgians that depend on byproducts that would be considered off flavors in other beers?

I've done it twice, and I do not do it anymore. One time it turned out alright, the beer was a hop bomb and I wouldn't say it was any better or worse than any other beer. The other time in a lighter beer it was not right, it was clean and I didn't notice any trub off flavors or contamination, it just tasted weird. I think if you are going from an Ordinary Bitter to a Barleywine it's a good idea, if you are doing a one dimensionally hoppy beer you can probably get away with it. However if you are doing anything that requires yeast characters or is light flavors in general it's not a very good idea.

The primary reason I don't is because it is so easy to measure out the right amount. It literally takes a minuet and you know your pitch rate. This way you know you are pitching the correct amount and if you want to reproduce the beer again you know how to.

Tonedef131 said:

The primary reason I don't is because it is so easy to measure out the right amount. It literally takes a minuet and you know your pitch rate. This way you know you are pitching the correct amount and if you want to reproduce the beer again you know how to.

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Well, a minute to measure the slurry, but 10 minutes to wash the carboy. I'm a lazy man, quite possibly the laziest man in Toledo. Which puts me in the running for laziest worldwide.

Seriously though, you just pour the cake into a measuring cup and pitch it into the next batch without washing the yeast? Are you able to leave the trub behind? This sounds like it might be the best of both worlds.

One of the times I pitched on a cake was when brewing a RIS with a belgian yeast. I used the cake for two reasons- first to provide a quick and healthy start to the yeast (the wort OG was 1.105), and the second was that I wanted "some" belgian flavor but not so much as to overpower the stout flavors.

I achieved the first goal, but not the second. I got next to no belgian yeast flavor, and what there was got completely lost in the dark roasty flavors. If I were to go back and do it over, that is one beer that I would definitely not pitch a whole cake.

ToledoDave said:

Seriously though, you just pour the cake into a measuring cup and pitch it into the next batch without washing the yeast? Are you able to leave the trub behind? This sounds like it might be the best of both worlds.

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Well I don't let any trub into my carboys, I chill in the kettle and let everything settle out before racking clear wort into my carboy. So other than maybe a little cold break formed during cold crashing there isn't really any trub to wash out.

Tonedef131 said:

I find it doesn't take more than a minuet to swirl up the yeast cake and dump it into a measuring vessel. When you overpitch at that extreme of a level the yeast will use up the nutrient and oxygen stores far too quickly. This will lower the vitality of the yeast and you also won't get much reproduction, which will substantially reduce many of the flavors we associate with beer.

You also will have no idea how much yeast you pitched, making it impossible to reproduce.

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I'm actually about to give this a shot for the first time in a few weeks when my ESB is done fermenting. What would be the desired amount to measure off? Is there some chart that would show me for different styles. I'm not planing on doing re-pitching for belgians, or wits. But was considering it between some ales, and potentially pitching a milk stout onto the cake from an amber ale.

Well, why not double up the next few batches you brew? Dump one on a cake and pitch the proper amount in the other and find out for yourself. For me, this is one of those areas that might not be noticeable to most palates - but it can definitely keep a good beer from becoming a great beer. I strive to make great beer

The whole lazy excuse is poor, it really takes 5 minutes to pitch proper yeast (slurry) amounts.

I've had great results when I pitch on the cake. I only do so when I need a very big yeast starter, I use the regular batch as a way to get enough yeast for something like a barleywine or IIPA.

I've pitched a Belgian tripel on a cake from a wit. It turned out delicious. No restricted ester production or anything like that, it was as estery as can be.

I've repitched 3 times in a row doing Edworts Haus Pale Ale. The second batch was better tasting and cleaner than the first but the third started getting a bread taste to it. Mind you it wasn't bad but you could tell the yeast was getting involved in the taste.
BTW I used Safale US-05.

BA_from_GA said:

I'm actually about to give this a shot for the first time in a few weeks when my ESB is done fermenting. What would be the desired amount to measure off? Is there some chart that would show me for different styles. I'm not planing on doing re-pitching for belgians, or wits. But was considering it between some ales, and potentially pitching a milk stout onto the cake from an amber ale.

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You can repitch any Belgian ales, there is no reason not to. You simply need to measure out how much yeast is needed so you still get the flavor profile you want. Use this calculator to find the desired quantity of slurry:
Mr Malty Pitching Rate Calculator

I've done this once, so not a huge sample size or anything, but if you go from light to dark, light to heavy color and flavor, smaller to bigger beer, I think pitching on the cake works very, very well. I doubt pitching the same kind of beer or going lighter will produce the same effect though. You need a beer big engouh and complex enough to steamroll any very minor changes in flavor that the trub from the previous beer might provide.

That said, the one time I did it, I was thrilled with the results, and will be doing it again.

Just make sure its the yeast you want to use, that it was not stressed in the first brew (too hot, high ABV, etc) and that the flavors from the first beer, in small quantities, wont be offputting in your next proposed batch.

Oh, and buy a blowoff tube. Like a rocket, I tell you.

mindcrime said:

Oh, and buy a blowoff tube. Like a rocket, I tell you.

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I use fermcap in the fermenter and that tends to keep them krausen under control as long as I am fermenting cool, which I always do because of the styles I like.

I just bottled an English IPA that I pitched onto an American Wit cake. US 05 yeast.

Took off in 2 hours, sprayed my ferm fridge out of the blow off tube bottle.

Tasted great at bottling. Will know more in 3 weeks.