'Splain yeast quantities to me, please

[olie]

Like the title says, I'd like someone to 'Splain yeast quantities to me.

WAIT! Not yet!

I understand about cell counts. I understand about wanting a healthy culture that will grow & chew away your sugars pooping-out delicious alcohol. I get that we want the yeast to out-grow any tiny bits of bacteria that might be in there. Those parts all make perfect sense.

What I don't get is:

* My package of yeast says its good for brewing up to 10 gallons.
* My 5 gallon recipe says to put in 2 packages (20 gallons' worth!)

Ok, that's the first thing. The second thing that's bugging me is: folks grow starters from weak/small yeast cultures to develop healthy, big, strong yeast cultures, right?!

* How come that same process can't happen inside the fermentor (carboy)?

That is: why can't I put, for example, 1/4 packet of yeast into my 5 gallon batch[1] and it just doubles & grows until it's the size of a full packet, then 2 packets, then that big blob of sludge that's going to end up on the bottom, anyway?

[1] NOTE: I'm not trying to be cheap with yeast; I'm just trying to better-understand the science of it. When the whole point is that X-amount of yeast will replicate & expand to eat the available yeast-food, I don't get why experienced folks are suggesting to start with 4x the manufacturer's recommended amount.

Is this just a matter of "making double (quadruple!) good & sure", big-hammer "it's an art, not a science" type of superstition stuff? Or is there really some reason why it matters?


Thanks!

P.S. Gentle, please. I'm a n00b, just trying to learn

 

[eric19312]

Well there is a book written for home brewers. The advice you are hearing is mainly consistent with the book. Give it a read... title is Yeast and you can get it from Amazon on Kindle too.

 

[JimRausch]

'Yeast' is a Great(!) book, but maybe beyond the ability of a newbie with the Qs above to understand. I'm not saying "don't get it", in fact "DO get it". A simplified answer is that yes olie, you are essentially correct- the yeast will continue multiplying until they have enough mass to do the job of fermentation, but..... during that initial multiplication it is producing a lot of metabolic byproducts, some of which give you strange flavors- the 'stressed yeast' flavor. Then you have given it a lot of work to do to grow new yeast cells, and may 'tire them out' before they finish the fermentation process yielding a higher FG then you were expecting. And finally, it takes time to grow all those new yeast cells- time that bacteria and other wild organisms can take advantage of and potentially grow quicker than the yeast you chose.
As an example, for lager fermentation, the general recommendation is to pitch twice the numbers of yeast that you pitch for ale fermentation. Why? Because the colder lager fermentation temps slow the yeast growth phase. So, in order to get a vigorous and complete lager fermentation you need a higher initial yeast mass.

 

[applescrap]

There is a good john palmer podcast on this. Cant remember which show. There is a lot in this and the questions you are asking require deep knowledge and insight from someone like palmer. Iirc, what little I know or care to the yeast eat sugar in an initial phase the they split. There are different phases to all this and different important factors to consider in each phase. Easy to see how from a macro level this is a high level discussion. The yeast when split or replicated to many times is not a good thing and too much (rare) can do something bad. Most under pitch, the packets i see and use mostly are theoretically only good for 5g dry and likely not enough. They have something like 150 billion cells if healthy but they degrade and a lot of beers require 200 or 250 billion. There are formulas and calculators and all that, but it is a great question once fermented or from starter there is enough for many batches. And it can be reused. If you really want to know how much yeast to use a calculator is it. For your other questions that palmer podcast or book. Sorry I hope I didn't tell you a bunch of stuff you already know or not help.

 

[renrutle]

A high level review of yeast biology:

There are several factors at play in life cycle of yeast that effect the final taste and aroma of your beer.

Yeast goes through two main phases during the fermentation process. The first is a growth phase in which the yeast cells multiply. This requires oxygen and is also called the aerobic phase. Once all the oxygen is consumed the yeast can no longer reproduce. During reproduction yeast produce several byproducts. Some are desirable; some, like diacetyl, not so much. Many of these by-products can be consumed by the yeast during the second phase.

The cleanup phase is anaerobic, meaning without oxygen. During this phase the yeast still consume sugar producing some different by-products. During this phase they also will consume some compounds produced during the areobic phase.


Theoretically you could start with a single yeast cell and ferment all of the sugars. However, there are a few problems that will need to be over come.

Yeast cell die so you will need to replace some of them to completely ferment all the sugars. This will require the addition of oxygen at come point during the fermentation. Introducing oxygen after fermentation is well underway can oxidize ethanol producing a paper/cardboard/vinegar flavor.

Yeast cells dead too long will breakdown (autolysis) and produce other off flavors.



Yeast reproduction math:

Assume you add 4 yeast cells and enough oxygen for them to reproduce once. You will get a 8 yeast cells.

Assume you add 1 yeast cell and the same amount of oxygen as before. After the first reproduction you will have 2 yeast cells and 3 units of oxygen left. The second reproduction will get you 4 yeast cells and one unit of oxygen left. One more cell can reproduce leaving you with 5 yeast cells and no more oxygen.

5 vs 8 does not seem like a big difference but ramp this up to 1 cell vs 1 billion cells or even 1 billion vs 2 billion and the final aerobic yeast counts will be vastly different.

With too few yeast cells you will not have enough to completely ferment all the sugar. With too many you will run out of sugar before all the secondary compounds have been produced or consumed.

The final flavor of your beer will be different in each case.

Take this as a very high level review. There is a great deal of science behind the pitching rate calculators. It is best to stick with their recommendation and adjust after a batch or two.

 

[RM-MN]

Brulosophy has a whole series on yeast pitch rates. I suggest you read all of them then think about what you are asking and what the results of the exbeeriments show. I think that getting the "perfect pitch" is more of a myth than actual science.

http://brulosophy.com/projects/exbeeriments/

Use the search bar for the term "pitch" and you will get about 10 articles to read.

 

[olie]

All excellent stuff, thanks!

I knew about aerobic vs anaerobic, and about the "race for control" (more yeast to beat-out bad bacteria for space/food), but reminders are always good. Someone else might come along and find this thread who doesn't know that stuff.

Two seemingly contradictory bits of info that maybe someone can clarify:

1) If the yeast have to replicate too often, they can "tire out".
2) You can save the (multiple-times replicated) yeast from batch #1 and use it to start batch #2, where it will replicate many more times, then gather that and use it for batch #3, etc., for a long-long time.

My memory of high school biology (and experience with sourdough starters passed down through generations) leans heavily toward (2), so I guess I'm mostly curious about (1) which seems like either superstition or I'm mis-interpreting what's being said, there. (Assuming good intent, I lean toward "me mis-interpreting", but can't figure out where I've gone astray, there.)

To repeat my original: I'm not trying to cheap-out on yeast -- I use what the recipe/calculator recommends -- I'm just trying to follow-along what's going on, here.

Regarding rerutle's 5/8 cells example: wouldn't a more accurate analogy be: (a) start with 10 yeast cells and 100-billion units of oxygen vs (b) start with 20-billion yeast cells and 100-billion units of oxygen ...? That's kind of the scenario I'm asking about -- an "all other factors being the same" sort of thing. That same thing holds true when talking about the dead yeast cells -- either way, at some point, there are billions of dead cells, no matter how many you start with. That's the thing I'm not connecting-up in my head.

Maybe the biggest part that I'm not quite grokking is the race to establish the strongest colony. I've been thinking of it as "eliminate unwanted bacteria", but maybe it's more like "there are unwanted bacteria in there, like it or not, so we need a bigger force of yeast to quash them with the minimum amount of fighting over resources. "Peace through superior yeast firepower"

I'll check out the book/podcasts recommended. Thanks again!

 

[HopHeavy]

All excellent stuff, thanks!

Two seemingly contradictory bits of info that maybe someone can clarify:

1) If the yeast have to replicate too often, they can "tire out".
2) You can save the (multiple-times replicated) yeast from batch #1 and use it to start batch #2, where it will replicate many more times, then gather that and use it for batch #3, etc., for a long-long time.

My memory of high school biology (and experience with sourdough starters passed down through generations) leans heavily toward (2), so I guess I'm mostly curious about (1) which seems like either superstition or I'm mis-interpreting what's being said, there. (Assuming good intent, I lean toward "me mis-interpreting", but can't figure out where I've gone astray, there.)

Both parts of this contradiction you cited can be true at different times. Of course, yeast don't really get "tired out" from replicating. They have been doing it for millenia. The term "tire out" might be replaced with a number of other terms. Some things to contemplate while you read up and listen to those podcasts...

A simple anecdotal about yeast growth: As we grow a yeast starter, we provide an aerobic environment in which several billion cells are encouraged to replicate themselves through budding. In a perfect starter these cells have adequate oxygen, zinc, nitrogen, etc. to bud healthy daughter cells. If not, they will make due as best they can, perhaps resulting in weaker cell walls or less permeable membranes. If deprived beyond a certain point they can actually alter their reproductive strategy altogether, wrecking your fermentation. Not likely to happen because we use DME for our starters. Minor changes may exhibit themselves in a varying fermentation speed or final gravity in our finished beer. The yeast might seem "tired out" if we can't get down to the anticipated gravity or it takes too long. We may not notice any difference at all.

On to collecting and reusing yeast... I believe you can find tons of articles around about spontaneous mutation, mutations caused by stressed yeast and unintentional selective culturing due to individual harvesting methods. All these concepts play into an idea that we should not reuse yeast more than a couple times. I don't have a big fear of spontaneous mutations as A) the incidence is something like 1 in 1,000,000, and B) I am looking forward to having my own house strain. My personal compromise is that I overbuild and harvest from starters rather than primary fermentations. Has worked so far. My culturing method is probably favoring the more flocculant cells as I sometimes collect without adequately crashing the starter.

Anyway, just some things to think about. Have fun!

 

[bradleypariah]

* How come that same process can't happen inside the fermentor (carboy)?

I have carefully read everyone's responses here, and I don't think anyone has touched on this, and I always wondered this myself. Here's how it was explained to me, and they were dumbing it down for me, so everyone feel free to correct:

If given an entire carboy of wort, a single yeast packet of 200 billion cells would rather get fat than reproduce, so they have a hay day stuffing themselves on sugar, getting amped up, then crashing. They then start producing too many digestive enzymes, like a person getting ill from over-eating. The yeast fall to the bottom, start bottom-feeding out of laziness, and many end up getting self-digested by their own enzymes.

When you make a starter, most of the yeast from the original packet are dead by the time you hit your target pitch rate, but they never autolyzed, they just lived out their lives in a more conservative environment, and reproduced a lot. Those dead and tired yeast are not making it into your carboy. You decant the starter to leave the dead/tired cells behind. You're doubling your cell count, but those cells you're pitching are the "daughters" and "grand-daughters" of the original packet, young and vibrant, and they're ready to chew through your wort. They aren't in such a hurry to get fat, because there's half the resources to go around. They're bumping into one another and concentrating on the oxygen, which equates to even more reproduction, which means even more healthy yeast that aren't self-digesting, so it's a cleaner fermentation.

I know someone else mentioned Brulosophy challenging this, but here me out:
I love Brulosophy, I never miss an episode, I visit the site almost daily. What I don't like is other people's interpretation of the data. Brulosophy always only changes one variable, and people wrongfully deduce that's bullet-proof science. They think that low-statistical results prove single variables are insignificant. I don't think that's Brulosophy's point. Brewing is A LOT of little variables, and if you F'ed with all the variables in a single batch, that's when you would see how much each of the little variables mattered to the bigger picture.

Sure, if you only change one variable - pitch rate -or- carapils -or- step mashing -or- using a secondary -or- squeezing the grain bag -or- black patent malt vs 120L..... and you might not pick up on the subtle changes.

But what if you made these two beers:
1) Single mash temp, .5# of 120L, no carapils, squeeze the grain bag, no sparge, middle-addition hops, low pitch rate, ferment too hot, leave on the yeast cake for a month
2) Step mash, .25# of black patent, with carapils (late mash addition), traditional sparge, hop stand at 170*, high pitch rate, fermented at 62*, transfer to new vessel directly following hitting FG, wait a week, then keg

I figure you catch my drift. All of those little details would fail to produce significance on their own, but beer #2 is going to wipe the floor with beer #1 (objectively). It ALL matters when taken into account together... so it exbeeriments with no statistical significance arguably only prove that if one off variable was the only mistake you made, you'll still most likely have a drinkable beer.

 

[Lifer59]

If I can tag along and have something ‘Splained to me? I buy a pure pitch and call that Gen 0. If I make a starter, is that Gen 1 and the beer Is Gen 2? Or is that whole beer a part of Gen 0?

 

[bradleypariah]

If I can tag along and have something ‘Splained to me? I buy a pure pitch and call that Gen 0. If I make a starter, is that Gen 1 and the beer Is Gen 2? Or is that whole beer a part of Gen 0?

There's no real gap between generations, and truthfully, a single yeast cell only dies after budding too many times. Its own outer hull becomes so scarred from splitting, that its cell wall doesn't lend itself to proper metabolism. Most yeast will bud anywhere between 10 and 40 times before death.
The budding of a single cell happens roughly every 90 minutes.

 

[applescrap]

@olie
Aghhh, just lost another post. It's my understanding that yeast do not tire out per say. The idea iirc is that if each yeast is asked to replicate too many times, then they don't like it and get stressed out. Basically a scenario of under pitching. Rather than replicating two or three times , each yeast is asked to replicate four or five times. I am not sure if those numbers are exact but it's something like that. The molecular processes of all this are well beyond anything that has been discussed on this thread so far. You will need to find that podcast and or the like if you are interested at that level. I would think the average home Brewer just wants to know, hey, does all this matter and like anything I fear the answer is yes and no. Too often in these discussions it has to be a matter of what's better or what's worse. The reality is each scenario creates more likely a difference. Is that difference bad or is that difference good. Quite possibly there are scenarios we're doing something that might be seen as bad can create something good and unique or special. It's my understanding that some Belgian yeast at high temperatures produce amazing flavors. Yet you can search page after page on this forum about how important fermentation temperature control is and it's very rare you will hear someone say it's a good idea to ferment really warm. Yet it's possible that in some situations this would be awesome. The real reality is that to find amazing and awesome beer would likely require someone to make a batch of beer with very little yeast and a lot of yeast. And to make each of those at very cold temperatures and very warm temperatures. Then get with a group of friends and blind taste them all to see which ones taste best. All of the great beers that we all love to drink are quirky in some way or another I'm sure. Okay I'm in the weeds sorry. Every beer is different, every yeast is different, every situation is different.

 

[madscientist451]

The lazy brewer way, breaking a bunch of "rules":
When using a new vial, I'll make a 2 gallon batch or make a starter, either using some wort from a current batch, some extract, or sometimes I'll put another gallon or two of water in the mash tun at the end of another batch, drain it off, boil it and make a 1 gallon batch. (some I will actually drink after fermenting). I don't decant the starter, I just swirl it up and chuck it all in the next batch. The same if I make a 2 gallon batch, all the yeast and anything else in the bottom of the carboy goes into a 5 gallon batch. The slurry from a 5 gallon batch goes into a sanitized quart jar and I'll user about 1/2 of it in the next 5 gallon batch.
The only time I've gotten off flavors is when I let the yeast sit around too long after fermenting is done (like several weeks or months) in warm weather. Get the yeast out of the carboy and in the fridge when its done.
I've stopped washing yeast, it doesn't seem to make any difference, but I'll usually discard a yeast after 5-6 runs and start over, but I have some yeast strains I've gone much longer with.

 

[cmac62]

I just started making starters, for the first few years of brewing I warmed up a WL vile/packet pitched it into the Fermenter and let it go. A lot of the time I never even saw my airlock bubbling, but I always figured beer was happening in the bucket. Low and behold every time it turned to beer. I'v used yeast from other batches, sprinkled dry and stirred it in and every other thing you can do and it has always come out with beer. I'm sure with proper pitch rate all of the prior beers would have been subtly different, but they tasted good to me. Anyway, I hope this helps too

 

[BrianDorry55]

I can only speak to my experiences...

I hate making starters, and almost never do it.

I make good beer that virtually never under attenuates. I usually have a very healthy aggressive fermentation within a few days that finishes quickly.

I buy very fresh yeast...almost always less than a month old from my homebrew store...I ferment at cool temps...and I shake the ever living hell out of the carboy after pitching.

I only use a starter if I’m making a high gravity beer, over 1.080...and even then sometimes I’ll just buy multiple smack packs.

I’m not lazy, just busy, and it works for me.