Define. Starter. Not. Amplification.

Ok. Question. Ready. Here we go...

The idea of a starter is to pitch yeast that is actively fermenting, i.e. during the stationary/fermentation part of the life cycle, right? Doing so allows the yeast to multiply and metabolize all the available oxygen during the log phase. Which leads into the stationary/fermentation phase (pitching stage). That way when you pitch, you have already amplified your yeast and they are ready to metabolize the newly available oxygen and cycle back to the log phase, in turn amplifying the yeast population once again.

If this is so, why are there so many people who see a need to crash cool their starters, therefore shocking the yeast and killing some of the population they worked so hard to amplify. Everyone who has vouched for this has had valid points for why they do this and I am not trying to cramp anyones style. I am merely trying to take some work out of brewing your tasty brews.

Some have said that they do not want the starter wort to get oxidized, but the wort can not be oxidized if the yeast are in the fermentation part of their life cycle. CO2 is blown out and O2 will not enter when CO2 is being expelled.

Others feel they do not want to throw off their numbers by adding an increased volume of wort and this is why the excess must be poured off. But honestly, a quart of starter wort, at most, is all that is necessary for a 5 gallon batch. That little volume of wort, which is now partly ethanol, mmmm ethanol.

Am I wrong in all of this.

There are two qualities with regard to yeast, viability and vitality. Vitality is health, viability is count of live cells. I doubt crash cooling "kills" many yeast, having probably minimal effect on viability. It probably does decrease vitality to a degree as the yeast goes dormant.

The other day I made a Koelsch which required a 6L starter. I have two 2L vessel to make starters in. So for practical reasons alone, it would be impossible for me to make a single 6L starter, so I stepped it up, doing 2L then 4L, crashing in between.

Have you ever tasted the spent wort from starters? Starters should be fermented warmer than fermentation temp, which results in off-flavors. For a 38L batch, 6L is about 15% of the beer volume. I would not want to have 15% of my beer to have fusels and other off-flavors.

So yes, if you're only doing a 1L starter in 5gal, maybe not a big deal. For a 2-3L starter in 5 gallons, I think the risk of poor flavor is not worth the risk of slightly reduced yeast vitality.

jlaureanti said:

The idea of a starter is to pitch yeast that is actively fermenting, i.e. during the stationary/fermentation part of the life cycle, right?

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Sorta. The idea is to increase your yeast's population and health. Some people swear by pitching yeast at high krausen, others prefer to pitch yeast that has already completed fermentation and gone dormant. Both work fine.

jlaureanti said:

If this is so, why are there so many people who see a need to crash cool their starters, therefore shocking the yeast and killing some of the population they worked so hard to amplify. Everyone who has vouched for this has had valid points for why they do this and I am not trying to cramp anyones style. I am merely trying to take some work out of brewing your tasty brews.

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Cold crashing doesn't kill the yeast. It actually causes the yeast to build up glycogen and trehalose reserves, which is valuable for the main pitch.

jlaureanti said:

Some have said that they do not want the starter wort to get oxidized, but the wort can not be oxidized if the yeast are in the fermentation part of their life cycle. CO2 is blown out and O2 will not enter when CO2 is being expelled.

Click to expand...

Getting oxygen into your starter is very important. The function of a stir plate is to do exactly that. That's also why you don't want an airlock on your starter flask. I don't think there's much doubt that spent starter wort is extremely oxidized, though whether or not that will be detectable in a biggish full sized batch is open for debate.

For me, a starter has very little to do with what you stated: "The idea of a starter is to pitch yeast that is actively fermenting, i.e. during the stationary/fermentation part of the life cycle, right? Doing so allows the yeast to multiply and metabolize all the available oxygen during the log phase. Which leads into the stationary/fermentation phase (pitching stage). That way when you pitch, you have already amplified your yeast and they are ready to metabolize the newly available oxygen and cycle back to the log phase, in turn amplifying the yeast population once again."

The idea of a starter is simply to increase the cell counts, as liquid yeast packages that are supposed to contain "100 billion cells" usually don't, and a starter is about increasing the quantity of yeast. Ideally, you'd pitch with the optimum pitch rate. Please see this article: http://www.mrmalty.com/starter_faq.php about 1/2 way down the page, that explains professional pitching rates and the idea that for an ale, you want to pitch around 0.75 million cells of viable yeast, for every milliliter of wort, for every degree Plato.

Nateo said:

There are two qualities with regard to yeast, viability and vitality. Vitality is health, viability is count of live cells. I doubt crash cooling "kills" many yeast, having probably minimal effect on viability. It probably does decrease vitality to a degree as the yeast goes dormant.

The other day I made a Koelsch which required a 6L starter. I have two 2L vessel to make starters in. So for practical reasons alone, it would be impossible for me to make a single 6L starter, so I stepped it up, doing 2L then 4L, crashing in between.

Have you ever tasted the spent wort from starters? Starters should be fermented warmer than fermentation temp, which results in off-flavors. For a 38L batch, 6L is about 15% of the beer volume. I would not want to have 15% of my beer to have fusels and other off-flavors.

So yes, if you're only doing a 1L starter in 5gal, maybe not a big deal. For a 2-3L starter in 5 gallons, I think the risk of poor flavor is not worth the risk of slightly reduced yeast vitality.

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The yeast vitality being only "Slightly" reduced is debatable, some feel it is considerably reduced. I don’t have any links or information to back this up...just experience. When commercial breweries build up yeast they brew a small batch and the next day they brew a second batch and throw it on the already fermenting smaller batch.

Yooper said:

Please see this article: http://www.mrmalty.com/starter_faq.php

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Yooper, thanks for this article. It answered a lot of questions I had.

King of Cascade said:

The yeast vitality being only "Slightly" reduced is debatable, some feel it is considerably reduced. I don’t have any links or information to back this up...just experience. When commercial breweries build up yeast they brew a small batch and the next day they brew a second batch and throw it on the already fermenting smaller batch.

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Maltfet already addressed that previously:

MalFet said:

Cold crashing doesn't kill the yeast. It actually causes the yeast to build up glycogen and trehalose reserves, which is valuable for the main pitch.

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And there is documentation to back that up.

On adaptive phases:

"As yeasts enter their dormant state, they build up glycogen reserves, and
so this adaptive phase is when the cells begin to awaken from their inactive state."
- http://www.mgriesmeyer.com/doatest/bjcp/yeastAndFermentation.pdf





On environmental changes (i.e., cold crashing):
(all the below quotes are from http://www.springerlink.com/content/1d21b9muaejd27th/fulltext.pdf)

"In fact, mutants lacking functional trehalose-6-P-synthase activity (tps1) are deficient in (at least) acquired thermotolerance and halotolerance (Lewis et al. 1995; Hounsa et al. 1998)."

"The enzymes required for both trehalose synthesis and hydrolysis in yeasts behave as general stress-responsive proteins."

"There is also a strong correlation between trehalose content and stress resistance in industrial baker’s yeast, but only in the absence of fermentation (Van Dijck et al.
1995)."

"The trehalose content of brewer’s yeast has also been proposed as an important indicator of cell vitality for optimizing fermentation in the brewing industry."

"Under conditions of freezing- or drying-induced dehydration, trehalose shows an exceptional capacity to protect enzymes and biological membranes. In addition, the rapid hydrolysis of trehalose by trehalase is necessary during stress recovery for cellular structures to be liberated from bound carbohydrate (Singer and Lindquist 1998)."




I'm a biology student, I could do this crap all day

Good info gentlemen. I'm glad to see there are differing ideas on how to go about this. As well as some info to back up some of the arguments!

Cheers