why does the pitch amount matter?

[frijole]

I don't understand why the amount of yeast pitched matters. Besides the speed that it will multiply. Doesn't it get to the same point no matter what?

 

[ifishsum]

I think there's more to it than that... variables like wort aeration can affect yeast reproduction and final cell count, so by pitching more yeast you're helping ensure a proper sized colony for fermentation even if something else was lacking. I'd think that the composition of the wort would make a difference as well, the amount of nutrients, etc. It also means the yeast don't get stressed as easily and should help reduce ester production and other possibly undesirable flavors. A good healthy quick start to fermentation is a good thing in my book and reduces your possibility of a stuck fermentation or unexpected flavors.

 

[yemu]

the yeast can't reproduce endlessly, and the amount of yeast that end up in the beer depend on how much you pitch. In some beers underpitching will cause underattenuation (it can happen if you pitch too low in belgian strong beers).

also you want to pitch the right amount of yeast to have the right amount of growth (which is associated with ester production which in many styles gives flavour and aroma to the beer). Overpitching is as wrong as underpitching (that is why it's not good to pour fresh wort on a whole slurry from previous beer - there's too much yeast in there)

 

[Joe_Stout]

Overpitching is as wrong as underpitching (that is why it's not good to pour fresh wort on a whole slurry from previous beer - there's too much yeast in there)

I've been told about 1 cup of slurry per 5 gallon batch. Does that sound about right?

 

[Bob]

I've been told about 1 cup of slurry per 5 gallon batch. Does that sound about right?

As in most things in life, 'It Depends'.



There are a wide variety of factors involved which make oversimplification - like 'pitch a cup of slurry per five gallons - dangerous. Different yeasts produce slurries of different density, which affects final cell count; the age of the slurry and the beer in the fermenter from which the slurry was harvested; the gravity of the wort into which the slurry is being pitched; the aeration of the fresh wort; all of these affect how much yeast is appropriate to pitch.

The best method IMO is to use the Mr Malty Calculator. It's tricky with slurry, but it's about the best place to start.

Cheers,

Bob

 

[Bob]

To the OP:

Yeast management is a very complex subject, one which can be daunting to the new brewer. Kudos to you for wanting to understand it!

Yeast management is more complicated than just knocking in a packet of yeast, sealing up the fermenter and forgetting about it. At least, it should be more complicated if you have the goal of brewing the best possible beer.

Yeast are living organisms and have very specific requirements for optimum, well, living. They are most productive within a fairly narrow set of parameters, and those can be manipulated to provide or enhance a specific result - one need only look at how fermentation temperature affects the final flavor of Bavarian Hefeweizen, for example.

Through centuries of practical experience, brewers have discovered certain Rules of Thumb. One of these is the practical amount of yeast cells needed to properly inoculate a given wort.

Knowing how much yeast to pitch - and how much you really are pitching - is something learned by reading and doing and educating oneself. For example, the Rule of Thumb is one million cells per milliliter of wort per degree Plato. For five gallons of wort at 1.048 OG, that approximates 225 billion cells. However, experience says that 75% of that number provides excellent results for ales, and ~125% of that number gives better results for lager beers.

The whys and wherefores are far beyond the scope of an Internet forum post. There are books out there, like Principles of Brewing Science, that explain far better than my poor power.

If you have more specific questions, though, I'll do my best to bore the crap out of you.

Bob

 

[Shawn Hargreaves]

Grossly oversimplified, yeast have a couple of different stages in their lifecycle:

- When they have both oxygen and a sugar supply, they reproduce like crazy, while consuming oxygen and giving off various complex byproducts

- When they run out of oxygen but still have sugar, they ferment that sugar and produce alcohol

- When they run out of both oxygen and sugar, they go into hibernation.

If you pitch a small amount of yeast, they must reproduce many times to create enough yeast to ferment the entire volume of beer. But this only works if they also have enough oxygen for this reproduction (which is why it is so important to aerate your wort especially for bigger beers). Also, the reproduction creates byproducts that contribute important flavors to the final beer. If there is very little yeast, there will be a lot of reproduction, and thus maybe too much of such flavors.

If you pitch a huge amount of yeast, less reproduction will be needed, and thus fewer flavors will be created. This is a good thing if you are going for a clean American ale, but probably not so desirable for a funky Belgian style.

 

[frijole]

I know enough microbiology to know that yeast go into an exponential growth phase at a certain point. So, it seems to me that as long as there is enough oxygen etc. that it shouldn't matter whether you start with one organism, or 1 billion. Assuming that the one survives of course.

The food the yeast need is a constant. The only difference between a lot of yeast and a little is how long it takes to consume that food.

 

[reim0027]

I know enough microbiology to know that yeast go into an exponential growth phase at a certain point. So, it seems to me that as long as there is enough oxygen etc. that it shouldn't matter whether you start with one organism, or 1 billion. Assuming that the one survives of course.

The food the yeast need is a constant. The only difference between a lot of yeast and a little is how long it takes to consume that food.

If I understand things correctly, that was Shawn Hargreaves's point of underpitching. The time it takes to produce enough yeast to fully ferment the wort. Too long in the exponential growth phase and you get undesired byproducts.

 

[Shawn Hargreaves]

My understanding is that the difference is in how many generations you are requiring the yeast to go through before it can settle down to fermentation. The more generations, the more funky flavors are produced, and also the more stressed out the yeast will be, which can adversely effect their ability to produce a clean beer and reach good attenuation.

 

[ifishsum]

Not to mention that the chance (however small it might be) of a non-intended organism taking hold ahead of your slow starting yeast during a long lag phase. Not likely a big concern with good sanitation, but a possibility nonetheless.

 

[Edcculus]

Jamil talks about pitching rates on his site.

Simply, pitching at proper rates makes for a better beer. Underpitching causes stressed yeast. I'd much rather overpitch. The point is to pitch the proper amount in the first place so fermentation starts faster. A fermentation that starts within a 12 hours of pitching is preferable to starting within 72 hours.

 

[frijole]

the undesirable byproducts make sense to me. But, the FG at the end should always be the same no matter the size of the pitch......right?

 

[ifishsum]

the undesirable byproducts make sense to me. But, the FG at the end should always be the same no matter the size of the pitch......right?

Not necessarily...otherwise why would the yeast manufacturers recommend starters or multiple packages for higher gravity brews? Wyeast recommends pitching one smack pack only on a wort up to 1.060. Above that they say to use two or even 3 packages (or make a starter)

 

[Edcculus]

It also depends. Vastly underpitching will lead to underattenuation. In theory, pitching one cell will create a lot of cells during its reproductoin phase. I'd say if you underpitched by an abnormal amount, your wort would not reach the same FG as the same wort pitched with the proper amount of yeast (0.75 million cells, for every milliliter of wort, for every degree plato. - mrmalty.com). I guess if you gave it enough time it might.

Also, if you could make beer with significantly less amounts of yeast, breweries would probably be doing it. In most instances, they are pitching more than .75 million/mm of wort/degree plato.

Its easy enough to make a starter though, so I say, why not pitch the proper amount?

 

[Shawn Hargreaves]

But, the FG at the end should always be the same no matter the size of the pitch......right?

No. If the yeast just got done frantically reproducing from a tiny starting volume, they will be stressed, tired out, and in no shape to embark on a mammoth fermentation project. As a result, they will conk out much earlier as the alcohol goes up and the sugars run out.

Think of it like a marathon. Who do you want on the starting line: well rested and healthy 20 year olds fresh from a nutritious starter, or scrawny and malnourished 10 year olds who just got done being raised by a teenaged mom?

 

[frijole]

that would be true if the yeast were old. But, they're babies. babies shouldn't be tired yet. They were just created.

sorry, this didn't really make sense, youre saying its good that they are older.

 

[remilard]

I know enough microbiology to know that yeast go into an exponential growth phase at a certain point. So, it seems to me that as long as there is enough oxygen etc. that it shouldn't matter whether you start with one organism, or 1 billion. Assuming that the one survives of course.

The food the yeast need is a constant. The only difference between a lot of yeast and a little is how long it takes to consume that food.

Sure if you continuously provide nutrients and oxygen you can grow as much yeast as you want. Growing yeast and making beer are not the same thing. Trying to do both at once is an excellent way to do a mediocre job of both.

 

[frijole]

im just saying there are say:

10 units oxygen and 10 units sugar in the wort (for arguments sake)

if you pitch 10 yeast that eat 1 oxygen and 1 sugar a day, you will consume the oxygen and sugar in 1 day.

if you pitch 1 yeast it will take 10 days to do the same job

but, either way the same amount of sugar and oxygen has been eaten

the end point is the same




I am not saying this is the way anyone should make their beer. I am just trying to understand why it is good to pitch more. besides it being faster, and less likely to get contaminated by a competing organism.

 

[PseudoChef]

During the reproduction phase, the yeast produce their phenols. Too long of a reproductive phase and the phenols in the finished product are going to be overwhelming.

 

[frijole]

that makes sense. thanks.

 

[Shawn Hargreaves]

that would be true if the yeast were old. But, they're babies. babies shouldn't be tired yet. They were just created.

That's not true even for humans. A child born to a healthy and well fed 20 year old mother will be very different to the baby of someone who was malnourished, who came under an undue amount of stress during the pregnancy, or who is way too young or too old.

This is even more the case for yeast than for humans. Mammals are designed to nurture and feed our babies, even at huge cost to the mother. But yeast reproduce primarily by cell division. Instead of mommy yeast and baby yeast, you have two copies each of which gets half of what used to be the mommy.

Concepts like age almost don't apply when you are dealing with single celled organisms!

 

[frijole]

you're right. I misunderstood what you said. I can see that now, they need to be more mature to have all of the necessary enzymes etc.

 

[Edcculus]

I haven't had a chance to listen to it yet, but I'm VERY sure The Brew Strong Episode on Yeast Starters will answer all of your questions and then some.

In the end, we are dealing with a living creature. Its not just a figure of # of yeast and oxygen. Pitching proper amounts of yeast have been proven by big breweries, homebrewers and award winning "celebrity" homebrewers like Jamil, Palmer, CP and more.