Why so much yeast?

[helibrewer]

I throw this out to gain a little more knowledge. I have yet to read Yeast but it's on my Christmas list.

I come from a wine background where we pitch about 1g/gal of yeast. Lallemand says that there are >15 billion viable cells per gram in their dry yeasts so in 5 gallons of wine must I would use 5 grams giving me >75 billion viable cells. Now mind you, this is for 23-25 Brix (about 1.101) which is much higher gravity than most beer we make.

So if I used Mr. Malty for this wine, it suggests 20 grams of yeast vice the 5 grams that is actually used.

Since wine and beer is made with the same critter (S. cerevisiae), that eats the same sugar, why does beer require 4X the amount of yeast that would be used on a similar gravity wine?

 

[KAMMEE]

The sugars are different, the maltose and maltotrios sugar chains are harder to break down and in order to make a beer without lots of fermentation off flavors, you need more yeast. Also, even after properly rehydrating dry yeast, there is no guarantee that it will be 100% viable. So, especially with dry yeast, Mr. Malty will suggest a higher pitch rate to ensure you get enough healthy, viable cells to ferment without producing phenols and esters that are not wanted.

 

[Dark_Ale]

Lots of outdated info on the net, lots of more knowledge coming forward with yeast pitches. I'm a homebrewer no pro but my 2 cents will say that one reason could be to get fermentation off to a quick start, and a quick healthy fermentation makes beer taste more better than a slow sluggish fermentation, and also a good fast fermentation will help overtake any nasties that may be present? I think camden is added to wine must to kill any nasty's 24 hrs or so before yeast is pitched. Some of the wine yeast also may attenuate more than beer yeast, and lagers are fermented cold so you need a big ol slurry to get it going and get the gravity down, like an oktoberfest(fermented cold) . Dont take anything I say to to bank

I have never had a problem with dry yeast when I rehydrate and pitch one pack in a 5 gallon batch, it always kicks off pretty quick.

Smack packs for me usually kick off quick in my experience as long as they swell pretty quick

The while labs vials I always make a starter if I dont its a long lag time.

I'm sure there are plenty more reasons, good question looking forward to other responses

 

[helibrewer]

The sugars are different, the maltose and maltotrios sugar chains are harder to break down and in order to make a beer without lots of fermentation off flavors, you need more yeast. Also, even after properly rehydrating dry yeast, there is no guarantee that it will be 100% viable. So, especially with dry yeast, Mr. Malty will suggest a higher pitch rate to ensure you get enough healthy, viable cells to ferment without producing phenols and esters that are not wanted.

I can get the complex sugar idea. My understanding from my biochem days (30 yrs ago) is that during the lag phase the yeast are multiplying until they reach their optimum concentration in the medium, once this concentration is reached, the alcoholic fermentation begins (exponential growth phase). So it seems that by pitching varying amounts all you are really doing is shortening or lengthening the lag phase...no matter how much you pitch, the yeast will multiply until the optimum population is reached, then go to work.

Or maybe not....

 

[RM-MN]

From what I understand about yeast is that they need certain things to multiply, one of which is oxygen or some replacement for that. When we brew our beer we put it in an airtight container and when the oxygen is used up, there will be no more multiplication of the yeast. If you aerate the wort well, there will be more oxygen available but then you risk the dreaded oxygenation of your beer that doesn't help the flavor. The optimum concentration for beer may be different from wine, I don't know.

 

[helibrewer]

From what I understand about yeast is that they need certain things to multiply, one of which is oxygen or some replacement for that. When we brew our beer we put it in an airtight container and when the oxygen is used up, there will be no more multiplication of the yeast. If you aerate the wort well, there will be more oxygen available but then you risk the dreaded oxygenation of your beer that doesn't help the flavor. The optimum concentration for beer may be different from wine, I don't know.

True, and I oxygenate my red wines even though they are open fermented and the cap is punched down several times a day. Whites are fermented in a closed pail (or carboy) with an airlock somewhere between ale and lager temps, basically identical to the beer process.

EDIT: I also oxygenate my pre-ferment wort and starters with pure O2

 

[KAMMEE]

You're correct about the growth phase, but the idea here is that if you pitch more yeast, they won't have to grow as many new cells from a small population. When the growth phase occurs, yeast produce bi-products that may not be wanted in the beer. To reduce the amount of bi-products and keep it cleaner, you start with a higher population of yeast. When you pitch into a full batch of wort, your goal isn't necessarily to grow yeast, if you were growing yeast you would want ideal conditions for that: primarily a 1.030 to 1.040 wort that doesn't have hops in order to keep the cells from being coated in hop oils which slow and slightly hinder growth, and a continuous source of oxygen. That would grow your yeast appropriately, but would not make very good beer.

 

[BrewKnurd]

I can get the complex sugar idea. My understanding from my biochem days (30 yrs ago) is that during the lag phase the yeast are multiplying until they reach their optimum concentration in the medium, once this concentration is reached, the alcoholic fermentation begins (exponential growth phase). So it seems that by pitching varying amounts all you are really doing is shortening or lengthening the lag phase...no matter how much you pitch, the yeast will multiply until the optimum population is reached, then go to work.

Or maybe not....

I'm pretty sure that the bulk of reproduction occurs in the exponential growth phase... that's why its called the exponential growth phase.

 

[helibrewer]

I'm pretty sure that the bulk of reproduction occurs in the exponential growth phase... that's why its called the exponential growth phase.

Yeah, I'm getting square on the specific phases now....this is from the Wyeast site:

"Many of the significant aromatic and flavor compounds are by-products of cell growth and are produced during the exponential phase. Many large breweries try to limit the amount of yeast growth by pitching larger quantities of yeast and therefore minimize ester synthesis. Keeping fermentations cold also limits ester production by limiting the rate of growth."

This isn't something that overly concerns wine makers (ester synthesis) so I'm starting to see the differences now....

 

[BrewKnurd]

Yeah, I'm getting square on the specific phases now....this is from the Wyeast site:

"Many of the significant aromatic and flavor compounds are by-products of cell growth and are produced during the exponential phase. Many large breweries try to limit the amount of yeast growth by pitching larger quantities of yeast and therefore minimize ester synthesis. Keeping fermentations cold also limits ester production by limiting the rate of growth."

This isn't something that overly concerns wine makers (ester synthesis) so I'm starting to see the differences now....

white labs also has a nice summary of the yeast life cycle: www.whitelabs.com/beer/Yeast_Life_Cycle.pdf

 

[Esmitee]

white labs also has a nice summary of the yeast life cycle: www.whitelabs.com/beer/Yeast_Life_Cycle.pdf

WOW That was an interesting read Thanks!