Why use yeast starter if yeast multiplies anyway?

[ocwo92]

I've brewed beer since 2011 but I somehow consider this a beginner's question anyway. It's just that I didn't really think about it until today when I brewed a beer and realized that I had purchased a liquid yeast instead of dry yeast and so should have made a yeast starter.

When I first began to brew beer, I knew nothing about yeast starters. Back then, at the end of the fermentation, there would always be layer of a half-inch or an inch of yeast at the bottom of the fermenter. I then learned about yeast starters and have used them since then, also producing a layer of about a half to an inch of yeast at the bottom of the fermenter.

This made me think a bit: with properly aerated wort, the yeast will immediately go forth and multiply until there's no more oxygen around. Only then does it begin to convert the sugars into alcohol. So why is it that I need a healthy yeast starter if the yeast grows until the oxygen has depleted anyway?

 

[Denny]

Because there's an optimal number of buddings/reproductive cycles that you want the yeast to go through. (I've heard 2-3 cited.) By pitching enough healthy yeast, they multiply just enough. If that was not the case, you could pitch one cell and eventually make perfect beer. We all know THAT doesn't happen!

 

[GoldenWeekendBrewing]

What would you use your Erlenmeyer Flask for? and stir plate and stir bar? Yeast starters are used, so we can spend more time brewing, buy more things, and pretend the beer tastes that much better!

- Jeff

 

[Qhrumphf]

Denny covered the important part- want an optimal amount of growth. The growth portion is actually what creates a lot of the important flavors from the yeast, good or bad, and too much or too little growth can increase flavors you don't want and/or suppress flavors you do want.

Just wanted to point out that there's a mechanism called the Crabtree effect. In the presence of even a very small percentage glucose, yeast will metabolize it into ethanol even in the presence of oxygen. There's more than enough glucose present in wort. In other words, ethanol conversion is happening from the very beginning. The fermentation process, while often expressed in phases, doesn't really work cleanly like you suggest, with one phase completely stopping and another starting. Lots of things are happening at once.

 

[GoldenWeekendBrewing]

My above post was said jokingly, but is more or less true. That being said, I always make a yeast starter, but I'm not sure it is helping reduce "off flavors," etc. Here is a decent RCT, regarding your very questions with interesting results.

http://brulosophy.com/2015/04/20/yeast-pitch-rate-single-vial-vs-yeast-starter-exbeeriment-results/

Basic science research doesn't always produce real world results, and brewing barrel's vs gallon's is also quite diffrent. RCT's (Radomized Control Trials) are the best way to get to the bottom of things. Maybe conduct a similiar experiement yourself?

 

[ocwo92]

In the presence of even a very small percentage glucose, yeast will metabolize it into ethanol even in the presence of oxygen. ... The fermentation process, while often expressed in phases, doesn't really work cleanly like you suggest

I'm aware of that, but sometimes it's easier to simplify things a little. In my case, I wanted to focus on the yeast growth.

 

[cannman]

There is a lot of yeast Info here,good books written, but here is the bare bone answer to your question:

Take the same yeast vial:

No starter = equals beer with flavor A

Starter B with same og and final og = flavor B

A does not Equal B

Pro Brewers say that beer made with starters or flavor B are better beers.


Now you can take that as truth or find out for yourself, but starters do a lot more for you than flavor like higher chance of hitting FG and making sure you get the right level of esters expected.

Jamil Zainasheff, author of Mr. malty and the Yeast book (with Chris White of White Labs Inc.) is a big proponent of yeast starters and you should read his material

 

[flars]

You may not need starter if you brew beers that have an estimated OG of 1.040 or less. Your entire wort would be a starter wort. Inoculation rate might be off but alcohol production will be low.

 

[ocwo92]

You may not need starter if you brew beers that have an estimated OG of 1.040 or less.

White Labs and Wyeast market their liquid yeasts as sufficient for a 5 gallon brew with an OG until about 1.070. Most brewers recommend yeast starers nonetheless.

In my case, I'm using a Belgian Ale yeast for a wort with an OG of about 1.070 and a little above 5 gallons, so I should have prepared a yeast starter as it's slightly underpitched otherwise. However, it's a porter with rather intense flavor malts, and the yeast is only a few weeks old, so any off-flavors caused by this accidental underpitching will probably be suppressed.

 

[ocwo92]

Because there's an optimal number of buddings/reproductive cycles that you want the yeast to go through. (I've heard 2-3 cited.) By pitching enough healthy yeast, they multiply just enough.

That's the answer I was looking for. Thanks, Denny.

 

[brewcat]

White Labs and Wyeast market their liquid yeasts as sufficient for a 5 gallon brew with an OG until about 1.070. Most brewers recommend yeast starers nonetheless.

In my case, I'm using a Belgian Ale yeast for a wort with an OG of about 1.070 and a little above 5 gallons, so I should have prepared a yeast starter so it's slightly underpitched. However, it's a porter with rather intense flavor malts, and the yeast is only a few weeks old, so any off-flavors caused by this accidental underpitching will probably be suppressed.

1.060 is what Wyeast says. I have never made a yeast starter with Wyeast even going a bit above that. No problems. But, wouldn't the smack pack be the yeast starter in that case? Where I would think a starter would be necessary is when you start reusing yeast.

 

[logan3825]

1.060 is what Wyeast says. I have never made a yeast starter with Wyeast even going a bit above that. No problems. But, wouldn't the smack pack be the yeast starter in that case? Where I would think a starter would be necessary is when you start reusing yeast.

No, the yeast pack for Wyeast is just enough to wake up the yeast.

 

[mongoose33]

Because there's an optimal number of buddings/reproductive cycles that you want the yeast to go through. (I've heard 2-3 cited.) By pitching enough healthy yeast, they multiply just enough. If that was not the case, you could pitch one cell and eventually make perfect beer. We all know THAT doesn't happen!

That's the answer I was looking for. Thanks, Denny.

Here's the question I have given Denny's and your responses: how did the yeast multiply in the starter? Haven't they burned up a certain number of budding/reproductive cycles anyway?

 

[brewcat]

NO, the yeast pack for Wyeast is just enough to wake up the yeast.

The nutrient packet must wake them up enough. I have never had a problem with Wyeast starting and finishing as it should.

Interesting stuff. I'd hypothesize that pitch rates should not only function from OG but also fermentation temps.

 

[Qhrumphf]

The nutrient packet must wake them up enough. I have never had a problem with Wyeast starting and finishing as it should.

Interesting stuff. I'd hypothesize that pitch rates should not only function from OG but also fermentation temps.

Pitching rate is a variable, like fermentation temp. And the two can influence a lot of the same characters, and can be manipulated accordingly. For example, with my Weizen styles, I ferment them fairly cold as otherwise the clove phenolic from Weizen yeast doesn't show as much as I would like. However, fermenting cold at normal pitching rates would completely decimate the banana ester. So as a result, I significantly underpitch them as well. Only way I've found to get the yeast expression the way I like it (a prominent amount of both banana AND clove, but a little heavier on the clove).

Issue is, while in general fermenting cooler will suppress esters that might be generated by a lower pitching rate, fermenting cooler is also more likely to cause underattenuation from underpitching.

 

[Denny]

1.060 is what Wyeast says. I have never made a yeast starter with Wyeast even going a bit above that. No problems. But, wouldn't the smack pack be the yeast starter in that case? Where I would think a starter would be necessary is when you start reusing yeast.

Wyeast has confirmed to me that there's so little nutrient in a smack pack that you get virtually no significant cell growth. I find that I get better performance by making a starter for any beer over 1.040. That's based on my own experience, not what Wyeast says.

 

[Denny]

What would you use your Erlenmeyer Flask for? and stir plate and stir bar? Yeast starters are used, so we can spend more time brewing, buy more things, and pretend the beer tastes that much better!

- Jeff

I have given up my stir plate and gone to 1 qt. "Shaken Not Stirred" starters. Results as good or better than stir plate and a hell of a lot easier.

 

[RachmaelBenApplebaum]

I think it's a good thing to mention yeast cell health and viability as part of the conversation. When you rehydrate (I hate using the word starter) you are essentially bringing the yeast cells back to life from being dried. For good cell wall health they need some sugar and a variety of micronutrients (I know most brewers don't use rehydration medium like go-ferm and go-ferm protect) in order to produce healthy bud sites without stress on the cell. All kinds of factors go in to yeast stress and they can typically be avoided altogether by being proactive and giving them a nice burst of energy right out of the gate so that by the time they're introduced to your medium (beer, wine, mead, etc.) They're ready to rock and roll. Everything from osmotic stress (too much sugar) to trying to re-pitch something that already has alcohol content (because you pitched dry the first time and got a stuck ferment, ask me how I know) requires that you have a happy, healthy, active population of yeasts that are acclimated to the environment of your medium. Hope this helps and happy brewing.

 

[Qhrumphf]

I think it's a good thing to mention yeast cell health and viability as part of the conversation. When you rehydrate (I hate using the word starter) you are essentially bringing the yeast cells back to life from being dried. For good cell wall health they need some sugar and a variety of micronutrients (I know most brewers don't use rehydration medium like go-ferm and go-ferm protect) in order to produce healthy bud sites without stress on the cell. All kinds of factors go in to yeast stress and they can typically be avoided altogether by being proactive and giving them a nice burst of energy right out of the gate so that by the time they're introduced to your medium (beer, wine, mead, etc.) They're ready to rock and roll. Everything from osmotic stress (too much sugar) to trying to re-pitch something that already has alcohol content (because you pitched dry the first time and got a stuck ferment, ask me how I know) requires that you have a happy, healthy, active population of yeasts that are acclimated to the environment of your medium. Hope this helps and happy brewing.

Dry yeast is a different scenario. We're talking about liquid cultures.

But I typically see it advised against using wort to rehydrate (go ferm and the like seems to be fine, not sure what those products are composed of). But most indicate that as long as it contains some hardness tap water is sufficient. Distilled water is not good.

However I seldom use dry yeast so far from my area of expertise.

 

[55x11]

I've brewed beer since 2011 but I somehow consider this a beginner's question anyway. It's just that I didn't really think about it until today when I brewed a beer and realized that I had purchased a liquid yeast instead of dry yeast and so should have made a yeast starter.

When I first began to brew beer, I knew nothing about yeast starters. Back then, at the end of the fermentation, there would always be layer of a half-inch or an inch of yeast at the bottom of the fermenter. I then learned about yeast starters and have used them since then, also producing a layer of about a half to an inch of yeast at the bottom of the fermenter.

This made me think a bit: with properly aerated wort, the yeast will immediately go forth and multiply until there's no more oxygen around. Only then does it begin to convert the sugars into alcohol. So why is it that I need a healthy yeast starter if the yeast grows until the oxygen has depleted anyway?

I think there are several purposes of the starter - it's to increase yeast's health, make it active, as well as provide growth to increase cell count.
In the controlled, small (2L or so volume), constantly aerated wort of medium gravity (1.030-1.040) that puts less stress on the yeast but at the same time provides opportunity for growth. Because the focus is on the yeast health, rather than quality of beer produced from the wort, you can accomplish this goal that is more challenging to do by pitching the vial of the dormant yeast directly into a high gravity beer, for example.

 

[Qhrumphf]

As far as the 1.060 per 5 gallons figure Wyeast and White Labs throw out there...

The "standard" accepted pitch rate amongst brewers for the right amount of growth (for both beer flavor, and for yeast health for reuse later) is 0.75 million cells per milliter of wort per degree Plato for ales and double that for lagers. I don't remember what the original source of this was, but this is based around repitched slurry, as is common amongst commercial brewing. And then that's not the be all end all, some beers would benefit from lower or higher rates depending on the target profile (variable that could be adjusted as I said earlier). But, in the "Yeast" book by Chris White and Jamil Zainasheff, it says that pure lab cultures (and not brewery harvested slurry), that rate can be cut in half. Vials and smack packs meet this criterion. Now, from what I understand JZ has actually tried to distance himself from that line, so take that for what it it's worth.

In any event, 5 gallons of wort is 18927.1 milliliters. 1.060 is 14.75°P. So 0.75*18927.1*14.75, you get 209381.04 million cells, ie you want 209.4 billion cells to achieve the above pitching rate. Cut that in half based on the above pure lab culture factor, and you're almost exactly at 100 billion cells, the amount in a White Labs vial or Wyeast smack pack.

Now, that's only going to work if your yeast is laboratory fresh and 100% viable. Which it won't be. How fast it's going to lose viability is up for debate, but it will lose some. Many accuse JZ's viability calcuator on Mr. Malty of being excessively conservative and showing much faster degradation than reality, so again take that for what it's worth.

But point is, 1 vial or smack pack in 5 gallons of 1.060 is pushing it, even if the yeast is fresh. You're better off making a starter.

 

[RachmaelBenApplebaum]

Dry yeast is a different scenario. We're talking about liquid cultures.

But I typically see it advised against using wort to rehydrate (go ferm and the like seems to be fine, not sure what those products are composed of). But most indicate that as long as it contains some hardness tap water is sufficient. Distilled water is not good.

However I seldom use dry yeast so far from my area of expertise.

You are discussing liquid cultures, OP just had a general yeast question. I'm pretty surprised that so few brewers utilize rehydration medium like go-ferm, it's more or less essential in my line of work.

 

[Bobby_M]

Here's the question I have given Denny's and your responses: how did the yeast multiply in the starter? Haven't they burned up a certain number of budding/reproductive cycles anyway?

The yeast doesn't have a limit on how many reproductive cycles they can go through. Denny's answer was talking about optimal flavor development in the actual beer as a result of the reproductive cycles. Pitching the right number of cells into the wort practically limits how many times they have to reproduce to reach terminal gravity.

The reason why you can grow the yeast in a starter without it affecting the beer is that the flavors kicked into the starter are isolated to 1-2 liters of wort which even if pitched in full get quite diluted. Alternatively the starter is allowed to settle in a fridge so that the nasty beer can be decanted off prior to pitching.

 

[Denny]

You are discussing liquid cultures, OP just had a general yeast question. I'm pretty surprised that so few brewers utilize rehydration medium like go-ferm, it's more or less essential in my line of work.

I don't even bother to rehydrate if the beer is under 1.080. Dozens and dozens of batches done like that and compared to rehydrating have convinced me that for my beer it just doesn't make a difference in the outcome. Yes, I know all the theory and numbers, but in the glass it doesn't seem to matter.

 

[Qhrumphf]

The yeast doesn't have a limit on how many reproductive cycles they can go through. Denny's answer was talking about optimal flavor development in the actual beer as a result of the reproductive cycles. Pitching the right number of cells into the wort practically limits how many times they have to reproduce to reach terminal gravity.

The reason why you can grow the yeast in a starter without it affecting the beer is that the flavors kicked into the starter are isolated to 1-2 liters of wort which even if pitched in full get quite diluted. Alternatively the starter is allowed to settle in a fridge so that the nasty beer can be decanted off prior to pitching.

My understanding, there was a limit to how many times a given cell was able to bud due to scarring left on the cell wall from the budding process. And unless under a lab conditions where nutrients, oxygen, pH, etc are precisely controlled, there was a practical limit to the growth that could be obtained during one growth "phase". Whether in a starter or a full batch of wort, under brewery conditions you couldn't practically obtain more than a 6x increase in total cell count in one "phase". In other words, if you pitch 100 billion cells into a full batch, it won't ever reach more than 600 billion. But if you pitch 100 billion cells into a starter, grow that up to 200 billion in the starter, you could then grow up as high as to 1.2 trillion in the full batch. Which poses the problem for single vials/smack packs into high gravity worts. They simply cannot reach the needed cell density to ferment properly without major stress, off flavors, and probably under-attenuation.

 

[ncbrewer]

I don't even bother to rehydrate if the beer is under 1.080. Dozens and dozens of batches done like that and compared to rehydrating have convinced me that for my beer it just doesn't make a difference in the outcome. Yes, I know all the theory and numbers, but in the glass it doesn't seem to matter.

Fermentis instructions are "Alternatively, pitch the yeast directly in the fermentation vessel providing the temperature of the wort is above 20°C (68°F). Progressively sprinkle the dry yeast into the wort ensuring the yeast covers all the surface of wort available in order to avoid clumps. Leave for 30 minutes, then mix the wort using aeration or by wort addition." Do you follow these instructions, or do you find they're really unnecessary?

 

[Denny]

Fermentis instructions are "Alternatively, pitch the yeast directly in the fermentation vessel providing the temperature of the wort is above 20°C (68°F). Progressively sprinkle the dry yeast into the wort ensuring the yeast covers all the surface of wort available in order to avoid clumps. Leave for 30 minutes, then mix the wort using aeration or by wort addition." Do you follow these instructions, or do you find they're really unnecessary?

I look at it as a guideline rather than a rule. I can't recall the last time I pitched at a temp over 63F and often lower.

 

[ocwo92]

My understanding, there was a limit to how many times a given cell was able to bud due to scarring left on the cell wall from the budding process.

New yeast cells multiply, too, so even if old scarface can no longer reproduce, his clones can. It doesn't take many cycles of exponential growth to reach a huge number of cells.

 

[madscientist451]

So why is it that I need a healthy yeast starter if the yeast grows until the oxygen has depleted anyway?

The quick answer is you don't NEED a yeast starter at all. Open the package and throw it in, eventually you'll have beer.
The longer answer is you may WANT to make a yeast starter because:
#1 You'll be drinking your beer sooner
#2 Your beer may taste better, or you might not be able to tell.
#3 You can empty your fermenter sooner and make more beer.
#4 You'll be able to sleep better at night because you'll have done as your told and conformed to common wisdom about all things beer.
I'll go out on a limb and say if you make two regular gravity beers one with a starter and one without, the differences may be noticeable, but probably not all that significant, so do what you want and enjoy your beer.

 

[mongoose33]

My understanding, there was a limit to how many times a given cell was able to bud due to scarring left on the cell wall from the budding process. And unless under a lab conditions where nutrients, oxygen, pH, etc are precisely controlled, there was a practical limit to the growth that could be obtained during one growth "phase". Whether in a starter or a full batch of wort, under brewery conditions you couldn't practically obtain more than a 6x increase in total cell count in one "phase". In other words, if you pitch 100 billion cells into a full batch, it won't ever reach more than 600 billion. But if you pitch 100 billion cells into a starter, grow that up to 200 billion in the starter, you could then grow up as high as to 1.2 trillion in the full batch. Which poses the problem for single vials/smack packs into high gravity worts. They simply cannot reach the needed cell density to ferment properly without major stress, off flavors, and probably under-attenuation.

This is the part I don't understand.

If you can only get a 6x increase in total cell count, what difference does it make whether the first doubling is in the starter or in the wort? It's as if that rule doesn't matter if you make a starter, but it does matter if you pitch directly into the wort w/o a starter.

What am I missing here?

And along those lines, how on earth do the yeast labs create the numbers needed to sell yeast to us, if there is this practical limit on how many times yeast can double?

I've read the Yeast book, btw, and this just isn't making sense to me.

 

[Qhrumphf]

This is the part I don't understand.

If you can only get a 6x increase in total cell count, what difference does it make whether the first doubling is in the starter or in the wort? It's as if that rule doesn't matter if you make a starter, but it does matter if you pitch directly into the wort w/o a starter.

What am I missing here?

And along those lines, how on earth do the yeast labs create the numbers needed to sell yeast to us, if there is this practical limit on how many times yeast can double?

I've read the Yeast book, btw, and this just isn't making sense to me.

There's a limit to how much an individual cell can bud. The new cells that it creates would then have the same limitation. Through successive fermentations it could be built up exponentially. From what I understand, a single fermentation is where that 6x limit comes into play, which I assume is a combination of the limit a certain cell can bud, and the yeast using up resources for reproduction rapidly getting rid of the possibility for limitless growth. Once a new fermentation is underway (say, in a batch of wort after the starter) and the yeast go through their full process again, starts over with all the new yeast created. I'm not 100% clear on the mechanisms behind it either. The Yeast book is where I read it, and in that particular facet I don't recall it being clear. I do know that in a lab, where dissolved oxygen can be measured and controlled, pH measured and controlled, and the exact nutrient content of whatever fermentation medium (likely not wort, probably closer to a nutrient rich go-ferm like substance) it's no longer the case, leading to my assumption above.

 

[ocwo92]

From what I understand, a single fermentation is where that 6x limit comes into play, which I assume is a combination of the limit a certain cell can bud, and the yeast using up resources for reproduction rapidly getting rid of the possibility for limitless growth.

I believe that the real reason we want to avoid too many multiplications of yeast generations in the wort may be that the high sugar content and the increasingly hostile (ethanol) environment makes the cell walls weaker, causing the cells to spill more off-tastes.

 

[brewerdoc]

The biggest reasons to use a starter are mainly applicable to that of the professional brewer. This is because time is money and one of the biggest things that pitch rate effects is time to finish fermentation. If you had a business and could pitch 2 times the yeast to finish 2 days earlier then that time is time that you can start brewing another beer and in turn make more money. For the homebrewer I'm not as convinced that a starter actually has that large of an impact on beer if you stick to usual pitch numbers and do not grossly under pitch or over pitch.

Here is the conclusion that I have come to after doing some research online.

• The amount of alcohol produced in various pitch rates did not vary
• pH of the beer did not vary
• Bitterness of the beer is an important quality parameter. It is caused by the α-acids of added hops, which are isomerised during wort boiling. In these studies there were no difference in bitterness between any of the beers
  Higher level alcohols were only slightly more predominant in those with higher pitch rates (propanol, isobutanol, isoamyl alcohol)
• Ester levels (compounds which often have a flowery taste and smell) did not differ in these studies***other studies in the past have found that higher pitch rates negatively affect ester production [1,2,3]***
• Diacetyl was present in dramatically higher amounts at the end of the fermentation’s with higher cell density (ranging from 19.1 ppb in the lowest pitch rate to 511 ppb in the second highest pitch group) Of note: there was a dramatic increase from 48 to 307 ppb from pitch rate of 20 to 40 X106 viable cells/ml. ***Other studies such as reference #5 have found the opposite may be true. I suspect this varies depending on the strain of yeast used.****
  

Many people also discuss about the number of replications of a certain yeast and a limit on this, well there is truth to this however the number of times varies per strand and per stress placed on the yeast. Most will say by 10 divisions the yeast culture needs to be replaced or purified to a single yeast as the starter. This is because as cells divide there may be a little miss match here and there of the genes of the yeast and over time this accumulates. If you don't separate out these cultures then after 10 generations you might effectively have a culture of the same yeasts with all various kinds of genes that might be producing all kinds of weird effects. It's not as if the yeast is tired and not producing any more compounds or ethanol, its just not longer close to being a pure or close to pure culture.


References:

1. Suihko M-L, Vilpola A, Linko M (1993) Pitching rate in high gravity brewing. J Inst Brew 99:341–346
2. Edelen CL, Miller JL, Patino H (1996) Effects of yeast pitch rates on fermentation performance and beer quality. Tech Q—Master Brew Assoc Am 33:30–32
3. Verbelen PJ, Van Mulders S, Saison D, Van Laere S, Delvaux F, Delvaux FR (2008) Characteristics of high cell density fermentations with different lager yeast strains. J Inst Brew 114:127–133
4. P. J. Verbelen et al. Impact of pitching rate on yeast fermentation performance and beer flavour. Appl Microbiol Biotechnol (2009) 82:155–167
5. Erten, H. et al. The Effect of Pitching Rate on Fermentation and Flavour Compounds in High Gravity Brewing. Journal of the institute of brewing. VOL. 113, NO. 1, 2007 pages 75-79

 

[smyrnaquince]

I think there are several purposes of the starter - it's to increase yeast's health, make it active, as well as provide growth to increase cell count.
In the controlled, small (2L or so volume), constantly aerated wort of medium gravity (1.030-1.040) that puts less stress on the yeast but at the same time provides opportunity for growth. Because the focus is on the yeast health, rather than quality of beer produced from the wort, you can accomplish this goal that is more challenging to do by pitching the vial of the dormant yeast directly into a high gravity beer, for example.

I also have never figured out why growing yeast in a starter was different than growing yeast in the wort, meaning I've never understood why a starter would help. I always figured that the yeast would grow either way, perhaps limited by the generation count mentioned in this thread.

The above posting is the first time I've gotten an explanation of the difference that I can understand.