Yeast Starter questions?

I put together a starter the other day from a slant I had made out of WLP840 American Lager Yeast, and posted my steps here. Well, I decided to pour some dregs from an earlier batch I had saved into the starter, and also move the stir plate to room temp (70F). Well, the first thing I remember noticing was the fizz/bubbles that are created at the top of the starter, and the color of the wort begins to change to a lighter color from the original unfermented wort.

This morning I took a gravity reading using my hydrometer and got around 1.020 which is good because the original gravity was 1.056. My question is that will this starter end up with a final gravity of 1.000 if I keep it on the stir plate for an extended period of time?

ipatch said:

I put together a starter the other day from a slant I had made out of WLP840 American Lager Yeast, and posted my steps here. Well, I decided to pour some dregs from an earlier batch I had saved into the starter, and also move the stir plate to room temp (70F). Well, the first thing I remember noticing was the fizz/bubbles that are created at the top of the starter, and the color of the wort begins to change to a lighter color from the original unfermented wort.

This morning I took a gravity reading using my hydrometer and got around 1.020 which is good because the original gravity was 1.056. My question is that will this starter end up with a final gravity of 1.000 if I keep it on the stir plate for an extended period of time?

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No... the yeast will reach their attenuation limit once they no longer can produce enzymes needed to break down the remaining dextrines in the wort.

It is very common in commercial breweries to put some wort on the stir plate and let it ferment out in 24-48 hours to see if the batch is properly attenuated. I know Stone does this for every batch they brew. It helps you detect problems in the process early, so you have time to brew another batch to blend to correct for example, and tells you what gravity is the terminal gravity your beer will finish at so you know when it's really done. It's called a fast ferment test, if you look around you will see some HBT members (kaiser) advocate doing it on every batch. A nice side effect of the fast ferment test is it gives you some yeast that are ready for propagation into another batch without the hazards of repitching yeast.

Saccharomyces said:

No... the yeast will reach their attenuation limit once they no longer can produce enzymes needed to break down the remaining dextrines in the wort.

It is very common in commercial breweries to put some wort on the stir plate and let it ferment out in 24-48 hours to see if the batch is properly attenuated. I know Stone does this for every batch they brew. It helps you detect problems in the process early, so you have time to brew another batch to blend to correct for example, and tells you what gravity is the terminal gravity your beer will finish at so you know when it's really done. It's called a fast ferment test, if you look around you will see some HBT members (kaiser) advocate doing it on every batch. A nice side effect of the fast ferment test is it gives you some yeast that are ready for propagation into another batch without the hazards of repitching yeast.

Click to expand...

Why would you say "NO" when this document specifically says that Lager yeast can "digest/use" all the available sugars in a wort?

The reason I ask this question is because I am trying to build a good starter for my next batch, and wanted to delve into to what makes a good starter a little more.

Well, I did a little more reading and I came across this document. It is a good read to help understand new terms concerning yeast, and the page gives this formula: Attenuation = [(OG-FG)/(OG-1)] x 100

So, using that formula, and plugging in the numbers I have recorded this is what I end up with:

Example: [1.056-1.022)/(1.056-1)] x 100

Attenuation = (0.034 / 0.056) x 100

Attenuation ~ 60 %


Alright, so a little more reading and the White Labs website states WLP840 has attenuation of 75%-80%, so using the formula presented above my starter needs to eat about 20% more of the sugars in the starter wort, and I should have a proper yeast colony to be pitched in my 5 gallon batch.

ipatch said:

Why would you say "NO" when this document specifically says that Lager yeast can "digest/use" all the available sugars in a wort?

The reason I ask this question is because I am trying to build a good starter for my next batch, and wanted to delve into to what makes a good starter a little more.

Click to expand...

When it says all available sugars it means all sugars that yeast are capable of fermenting. There are some sugars and other things in wort that no yeast, lager or ale, will eat. Unless your "wort" was boiled table sugar you are not going to get down to a FG of 1.000.

ipatch said:

Why would you say "NO" when this document specifically says that Lager yeast can "digest/use" all the available sugars in a wort?

The reason I ask this question is because I am trying to build a good starter for my next batch, and wanted to delve into to what makes a good starter a little more.

Click to expand...

First off, there are some sugars, such as maltodextrine, that brewing yeast can't ferment effectively. Second, the grain contributes lots of other "stuff" that isn't sugar. However, the alcohol produced by yeast is less dense than water, so it's theoretically possible to end a ferment at an SG less than 1.0. This is uncommon in beer, but fairly common for wine and cider.

The bigger question is this: So what? Ask yourself this: What's the point of making a starter? Is it to ferment all the sugars in the starter, or is it to produce an adequately sized "crop" of yeast for pitching into wort? I hold that it's the second, rather than the first.

There are a lot of avenues to the goal of pitching plenty of healthy yeast, and more than one of them are right. I just think that if you focus on the fermentability of the starter wort rather than the health of the yeast, you may be heading somewhere that's not going to help you make good beer.

And, at the end of the day, that's what it's about: Good beer.