Over and underpitching

[gatewood]

Hey guys!

I've been making my brews, always making sure to have a yeast starter handy, and I usually poured about 50ml of the thing on each new batch, and it always worked just fine.

However, I recently came across an article describing this thing about adding too much or too little yeast into your wort (over and underpitching). It only talked about how, if you add too little yeast, it'll use up all of the available oxygen budding/splitting (reproducing) and that, you'll be left with a bunch of old, exhausted yeast and just some new ones that won't be enough to get the job done, and the whole thing will reach very under attenuated levels at best.

I wanted to know more about the subject but didn't quite find satisfactory data (or forums talking about stuff too specialized for me understand), so I decided to turn to the professionals for some professional advice:

What exactly goes on if your wort is added too little, or too much yeast?

 

[jddevinn]

Typical pitch rate is calculated as

Ales Yeast Cells Required = (0.75 million) X (milliliters of wort) X (degrees Plato of the wort)
Lagers = (1.5 million) X (milliliters of wort) X (degrees Plato of the wort)

There are a lot of calculators online to estimate the Viability of the yeast you start with and calculate what you need to make for a starter. I typically overbuild the starter and then save 100 billion cells to make the starter for the next beer for ~5-6 generations.

Popular calc is Mrmalty.com
I use one I based off of Homebrew Dad's Online Yeast Starter Calculator
I also decant between each step and at the end (after pulling off the overbuild) to get the least amount of starter wort into the wort.

 

[jddevinn]

This is a good, cheap, about the right amount of in depth book for homebrewers

 

[Dland]

I'll add my free advice, for what it is worth:

Seems like many of the "yeast calculators" numbers sometimes don't bare out with "facts on ground".

I follow instructions on the yeast packs I use, not because I don't know any better, but because they make sense, and I don't spend twice as much on yeast in a batch than I needed too, and did not have to mess w starter unless it is warrented by special considerations. There is a bit of an over pitching cult on this forum in my opinion.

However, when you bring up oxygen scavenging as a negitive effect of "under pitching", this can easily be resolved by active oxygenation, making for properly pitched oxyegenated wort.

I often use O2 injection when transferring wort, (one also can do in fermentor with O2 wand/stone). I always use O2 when it is not a first pitch of yeast.

Great results so far, just crashed 10 gal batch #102.

 

[slayer021175666]

My 2 Cents?
Don't dwell on it. If everthing is working fine, just go with what you been doin'! The majority of homebrewers have no equipment to actually count cells and too much gobilygoop from the science side can spoil a good time and an otherwise good beer. If completely calculated yeast is an aspect of brewing that intrests you, go for it! Learn all you can! But, if its just an article that you read and it caused you concern or worry, drop it and keep having fun with the hobby.

 

[slayer021175666]

oh, sorry. Too much yeast gives overflowing beer through the airlock. Often a huge mess and a loss of beer. Under pitching gives slow or non-existent fermentation and a big lag time before it ferments. This gives a time window where other microbs and nasties can infiltrate because of the lack of alcohol in the wort that would otherwise kill them.

 

[gatewood]

I'll add my free advice, for what it is worth:

Seems like many of the "yeast calculators" numbers sometimes don't bare out with "facts on ground".

I follow instructions on the yeast packs I use, not because I don't know any better, but because they make sense, and I don't spend twice as much on yeast in a batch than I needed too, and did not have to mess w starter unless it is warrented by special considerations. There is a bit of an over pitching cult on this forum in my opinion.

Well, in my experience, starters do indeed get the brew going a bit faster and seem to completely eliminate the risk of underpitching. They also reduce costs, since you can reproduce the yeast and then pour the starter into multiple batches.

Well, by simple logic, one would think that, overpitching should be a desirable thing to do, since, the more yeast you have around, the faster the batch will get attenuated. Im aware its more complicated than that and, Im probably wrong in multiple places and I'd like to know where those places are.

However, when you bring up oxygen scavenging as a negitive effect of "under pitching", this can easily be resolved by active oxygenation, making for properly pitched oxyegenated wort.

I often use O2 injection when transferring wort, (one also can do in fermentor with O2 wand/stone). I always use O2 when it is not a first pitch of yeast.

Great results so far, just crashed 10 gal batch #102.

"O2 injection" what exactly you mean by that? I usually shake my starters and my worts to oxygenate them and give the yeast a good headstart, at the cost of a bit of sugar being turned into CO2 (though I capture that too to grow plants).

 

[gatewood]

My 2 Cents?
Don't dwell on it. If everthing is working fine, just go with what you been doin'! The majority of homebrewers have no equipment to actually count cells and too much gobilygoop from the science side can spoil a good time and an otherwise good beer. If completely calculated yeast is an aspect of brewing that intrests you, go for it! Learn all you can! But, if its just an article that you read and it caused you concern or worry, drop it and keep having fun with the hobby.

Thanks for the input. Im interested in delving as much as possible into the whole subject

oh, sorry. Too much yeast gives overflowing beer through the airlock. Often a huge mess and a loss of beer. Under pitching gives slow or non-existent fermentation and a big lag time before it ferments. This gives a time window where other microbs and nasties can infiltrate because of the lack of alcohol in the wort that would otherwise kill them.

I see, guess my use of a starter saved me from plenty of headaches and ruined batches... anything else you might wish to share?

 

[Beermeister32]

I've heard yeast counts are always an approximation due to the different sizes of yeast cells.

 

[Dland]

Well, in my experience, starters do indeed get the brew going a bit faster and seem to completely eliminate the risk of underpitching. They also reduce costs, since you can reproduce the yeast and then pour the starter into multiple batches.

Well, by simple logic, one would think that, overpitching should be a desirable thing to do, since, the more yeast you have around, the faster the batch will get attenuated. Im aware its more complicated than that and, Im probably wrong in multiple places and I'd like to know where those places are.


"O2 injection" what exactly you mean by that? I usually shake my starters and my worts to oxygenate them and give the yeast a good headstart, at the cost of a bit of sugar being turned into CO2 (though I capture that too to grow plants).

O2 injection is done with an in line device, in this case one attached to fermentor, that allows one to inject o2 into the wort stream as it enters the fermentor. I used a regular stone/wand oxyegenator for a while though, with good results, but it is a bit less elegant sanitation-wise.

I'm OK with $4 for one pack of ale yeast, eg US-05, or $12 for two packs of lager yeast, eg S-189, for 10 gallons., specially since I usually make two or three batches in a row without breaking down fermentor, so it usually costs less than that.

 

[gatewood]

O2 injection is done with an in line device, in this case one attached to fermentor, that allows one to inject o2 into the wort stream as it enters the fermentor. I used a regular stone/wand oxyegenator for a while though, with good results, but it is a bit less elegant sanitation-wise.

I'm OK with $4 for one pack of ale yeast, eg US-05, or $12 for two packs of lager yeast, eg S-189, for 10 gallons., specially since I usually make two or three batches in a row without breaking down fermentor, so it usually costs less than that.

oooh... ok I see, you mean like those things they put in fish tanks.

hmmm... now what do you mean with "breaking down the fermentor?"

 

[Dland]

oooh... ok I see, you mean like those things they put in fish tanks.

hmmm... now what do you mean with "breaking down the fermentor?"

Not fish tank gear, although that might work, might not be as easy to sanitize, this is injector I have:
https://www.morebeer.com/products/ss-brewtech-inline-oxygenation-kit.html
This is the wand:
https://www.morebeer.com/products/oxywand-2-micron.html
Break down fermentor; take apart all the parts of a conical fermentor to clean and sanitize. I have found I do not have to do this with each batch, since it is kept sealed and trub dumps and rack downs displaced by CO2.

This allows me to put new wort on yeast cake in recently emptied fermentor. I will only do this if fermentor is going to get new wort within a short time of racking, and have so far only gone 3 batches between cleaning and sanitation, though usually it looks like I could have gone further batch(s) when I open it up even after 3 batches.

 

[jddevinn]

I follow instructions on the yeast packs I use, not because I don't know any better, but because they make sense, and I don't spend twice as much on yeast in a batch than I needed too, and did not have to mess w starter unless it is warrented by special considerations.

Batch size plays into this as well. One 'pack' of yeast may be sufficient for most 5 gal batches but when you brew larger amounts purchasing new yeast gets expensive. Overbuilding starters and then saving reduces the cost of yeast as it can be used for multiple generations.

Brew variety plays a part as well. I don't always use the same yeast repeatedly. Overbuilding and saving allows for a moderate sized collection of yeast to be stored.

There is a bit of an over pitching cult on this forum in my opinion.

Brewing Science and Practice

The actual pitching rate used varies considerably between breweries and rates of 5 to
20 million cells/ml of wort are common depending on the specific gravity of the wort. An
optimum level is considered to be 10 to 12 million cells/ml and this should result in a
reproduction rate for lager yeast of 3 to 5 times

This lines up with the formula I quoted above. I don't think overpitching is a "cult", range of yeast requirement is a known science. Although of course cell count is estimated.

"O2 injection" what exactly you mean by that? I usually shake my starters and my worts to oxygenate them and give the yeast a good headstart, at the cost of a bit of sugar being turned into CO2 (though I capture that too to grow plants).

8-12 ppm Oxygen in the Wort at beginning of fermentation is a typical requirement.
Oxygenation / Aeration | Wyeast Laboratories

 

[Qhrumphf]

Another big factor with pitching appropriately is the health of the yeast on the other side. Both over and under pitching negatively impact the health of subsequent generations. If you don't repitch from batches (whether using fresh yeast over time or overbuilding starters instead of harvesting from full batches), then that may be less of an issue for you.

Pitching rate is a variable that can be adjusted like anything else. Both overpitching and underpitching have their risks, but an overpitch is typically safer than an underpitch.

Even if you do actually count cells under a microscope, you're STILL approximating (since you're extrapolating total numbers from small diluted samples), though it's by far the most accurate. Most commercial breweries will look under a microscope to verify approximate cell density, and then from there harvest and pitch yeast by weight, not volume.

 

[Dland]

Batch size plays into this as well. One 'pack' of yeast may be sufficient for most 5 gal batches but when you brew larger amounts purchasing new yeast gets expensive. Overbuilding starters and then saving reduces the cost of yeast as it can be used for multiple generations.

Brew variety plays a part as well. I don't always use the same yeast repeatedly. Overbuilding and saving allows for a moderate sized collection of yeast to be stored.
Brewing Science and Practice
This lines up with the formula I quoted above. I don't think overpitching is a "cult", range of yeast requirement is a known science. Although of course cell count is estimated.

8-12 ppm Oxygen in the Wort at beginning of fermentation is a typical requirement.
Oxygenation / Aeration | Wyeast Laboratories

Only responding since you quoted me, but it looks like you responded to my posts w/o reading them completley. Pitch away my friend, spend time w starters and all, try to keep them clean, never implied there is anything wrong w that. I'm glad you got brew books to quote, I just have well informed tests, trial, error, science, and learning by doing. Have a great evening, and most of all, enjoy your beer.