How Much is Too Much Yeast?

[twitt]

I recently threw an American Ale (AG) onto a yeast cake from a Victory Hop Devil clone (Extract). I do 5 gallon batches when I brew and have been re-pitching the yeast like this for a few batches. I've been saving it in a 64oz bottle in the 'fridge in-between batches. I haven't detected any off-flavors, but wouldn't really know what to look out for even if there were any. I've read elsewhere that dead yeast cells aren't good, but what are the negative effects (if any) of pitching too much yeast?

Photos here (scroll to the bottom of the page):
http://www.TheBitterBrewer.com/viewtopic.php?f=13&t=26

[talkingseagull]

you can over pitch, but it ain't easy...

http://www.fermentarium.com/content/view/183/58/

[majorvices]

Going directly on a low gravity yeast cake with a low gravity beer would be over pitching by way too much. You will make beer. But you will make better beer if you try to pitch in the correct range.

[taeagan]

On the homebrew scale it's virtually impossible to determine whether or not you're pitching the proper amount of yeast. You have very little ability to determine the quantity and viability of the yeast. How old is it? What percentage of the slurry is actually yeast and not beer or trub? You can use a calculator like on mrmalty.com, but that's nothing more than an educated guesstimation. And it is always better to overpitch than underpitch. So as the man says... rdwhahb.

[beardog]

So what are the negative side effects of overpitching?

[taeagan]

That the finished beer might taste lifeless or lack complexity - certainly characteristics that are even more subjective than the usual descriptors. Possibly overattenuation.

Personally, I can't recall ever coming across a beer that made me think "this was probably overpitched".

[beardog]

So if I ever wanted to make a commercial american lager I should overpitch? This is a serious question, I want to prove just once that I can do it to my lame friends who drink that stuff all the time.

[taeagan]

Generally speaking, unless you get a gallon jug of fresh yeast slurry from a professional brewery, you should not worry about over-pitching. You should be less worried about overpitching a lager than an ale, and you should be even less worried about overpitching an American lager than any other lager. If you're brewing an American lager, pitch a lot of yeast, give it a bunch of O2, and ferment it as low in the yeast's temperature range as you can. If you're pitching a lot of yeast in a lager like this the best way to do it is to pitch it at a temperature a few degrees lower than the yeast's preferred range and let it free-rise up to the fermentation temperature. This minimizes the production of esters during the growth phase. Good luck.

[majorvices]

On the homebrew scale it's virtually impossible to determine whether or not you're pitching the proper amount of yeast. You have very little ability to determine the quantity and viability of the yeast. How old is it? What percentage of the slurry is actually yeast and not beer or trub? You can use a calculator like on mrmalty.com, but that's nothing more than an educated guesstimation. And it is always better to overpitch than underpitch. So as the man says... rdwhahb.

I agree with what you are saying, but not completely. I did a series of Hefeweizens this summer in which I intentionally over pitched by running the starters on stir plates and pitching probably about 2xs as much yeast. I found I got more banana esters by over pitching and more spice by slightly underpitching (pitching a one Liter starter at high krausen). These were fermented with WLP380 IV strain in the high 50/s low 60s.

Learning how to use a yeast to get it what you want it to do involves learning the approximate amount of yeast you need to pitch. I agree that on the HB and even small brew pub level it is impossible to be precise - but it is good to get close and there is a gray area,

I wrote a bunch about over pitching hear earlier this AM: viewtopic.php?f=26&t=70147

[HomeBrew]

Learning how to use a yeast to get it what you want it to do involves learning the approximate amount of yeast you need to pitch. I agree that on the HB and even small brew pub level it is impossible to be precise - but it is good to get close and there is a gray area

The best thing we can do on th HB scale is to keep procedures consistent. Whether you are pitching active starters or slurries, keeping the wort type/ SG, inoculation rate, incubation temps, growth times, etc. are all very important. It still won't be precise, but you can better determine the affects of pitch rate once you standardize these variables.

[Kaiser]

I did a series of Hefeweizens this summer in which I intentionally over pitched by running the starters on stir plates and pitching probably about 2xs as much yeast. I found I got more banana esters by over pitching and more spice by slightly underpitching (pitching a one Liter starter at high krausen). These were fermented with WLP380 IV strain in the high 50/s low 60s.

That’s what is commonly found in the brewing literature: more yeast -> more esters. But so far there have been little reports by home brewers that confirm this. And most home brewing literature also states the opposite.

Thanks for running this experiment.

One concern about repitching an old slurry/cake is the amount of dead cells in there. As yeast gets old and dies it starts to release compounds that are detrimental to beer quality. One of them is a protein degrading enzyme that can hurt your head retention.

I’m a proponent of either growing new yeast for each batch or using yeast that is no more than 2 weeks old from the time it was pitched. If you keep yeast sediment for a long time I recommend taking a small sanitary sample (about a tbsp worth) and step that up until you have enough for pitching.

Kai

[bluesman]

One concern about repitching an old slurry/cake is the amount of dead cells in there. As yeast gets old and dies it starts to release compounds that are detrimental to beer quality. One of them is a protein degrading enzyme that can hurt your head retention.

I’m a proponent of either growing new yeast for each batch or using yeast that is no more than 2 weeks old from the time it was pitched. If you keep yeast sediment for a long time I recommend taking a small sanitary sample (about a tbsp worth) and step that up until you have enough for pitching.

Kai

Very interesting Kai. Where did you find the data to support this mechanism.

[Kaiser]

I came across this in Kunze’s “Technologie Brauer und Maelzer”. There is also an English version that some homebrewers seem to own as I occasionally see references to this book.

He is rather adamant about the negative effects of dead yeast and how important healthy yeast is. Now this comes from commercial brewing and I don’t know at what level it becomes detrimental enough that we homebrewers also have to worry. It’s not the most important thing, but if you can make sure your yeast is as fresh as possible.

The enzyme is called protinase A and is secreted by the yeast during fermentation. Especially under stress (e.g. high alcohol levels). If you search Google for “proteinase A beer head” you’ll find a number of links to scientific studies. From this I take that there is a large interest in controlling and understanding this particular enzyme.

Kai

[twitt]

I’m a proponent of either growing new yeast for each batch or using yeast that is no more than 2 weeks old from the time it was pitched. If you keep yeast sediment for a long time I recommend taking a small sanitary sample (about a tbsp worth) and step that up until you have enough for pitching.

So if I take your advice on making a new starter from the yeast cake, then would it make sense after a batch is harvested to rinse the slurry with water, let it settle for a day or two, pour off the top liquid, then scoop a tablespoon of slurry from the top of what remains? I'm guessing that this would be the best yeast to grab as it'll contain the least amount of trub. Your thoughts?

[Kaiser]

So if I take your advice on making a new starter from the yeast cake, then would it make sense after a batch is harvested to rinse the slurry with water, let it settle for a day or two, pour off the top liquid, then scoop a tablespoon of slurry from the top of what remains? I'm guessing that this would be the best yeast to grab as it'll contain the least amount of trub. Your thoughts?

If you are taking a fairly small samle in order to grow a lot more yeast from it, don't bother about the little trub you will be getting with this. Washing the yeast would remove that trub but also increases the risk of infection (every yeast handling step increases the infection risk) w/ much benefit.

So don't bother.

Kai