[morticaixavier]

so "as long as the gravity is low" and "wont be making alcohol"....not sure i get that. low OG still makes alcohol, no? how low we talking about.

Brewing yeast can both respire (requires presence of fee oxygen) and ferment (which does not).  However, even in the presence of oxygen, yeast will ferment rather than respire if there is sufficient glucose present (the Crabtree effect).

I've seen different figures listed for the glucose threshold, including 0.3%, 0.4% and 0.5% w/v.   

ok makes sense. so how do you make a starter that builds new yeast without glucose?

The Yeast labs have propagators that continuously feed the yeast sub 1.009 wort and o2. this keeps them below the crabtree threshhold so they stay in full aerobic reproductive mode.

[Wort-H.O.G.]

That's cool- guess we won't be replicating that process at my house!

[Wort-H.O.G.]

So while we are on the topic- what's the forum think for generations for non propagated low glucose starters? If I'm taking slurry from a batch, and then taking about 1/3 cup and building a new starter for the next batch- how many times would one consider this a good practice before you want to move on to a fresh vial of yeast?


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[a10t2]

how many times would one consider this a good practice before you want to move on to a fresh vial of yeast?

The typical answer is 5-10 generations, but if the sanitation is good and it's still performing consistently, I'll go longer. I think in Yeast they recommend 5 generations.

[Wort-H.O.G.]

how many times would one consider this a good practice before you want to move on to a fresh vial of yeast?

The typical answer is 5-10 generations, but if the sanitation is good and it's still performing consistently, I'll go longer. I think in Yeast they recommend 5 generations.

ok. i just recently started to repitch as ive always just got a new vial and made a starter. im on my 3rd round of repitch and so far so good (after my first hiccup).

[thebigbaker]

Interesting replies, thanks for all the info and feedback everyone!

[S. cerevisiae]

Depends on how you make your starter. If you keep them in the respiratory stage then it does not count as a gen. If you make a simple, unstirred/unaerated starter then that counts as one gen.

Least, that's how I understand it.

Yeast do not respire in the presence of glucose levels above the Crabtree threshold.  All beer worts, even 1.020 starters, are above the Crabtree threshold.  All growth above the Crabtree threshold is fermentative growth. However, in the presence of dissolved O2, a small amount of glucose is shunted to the respiratory metabolic pathway for the synthesization of ergosterol and unsaturated fatty acids.

[S. cerevisiae]

My question is, with each new starter I do, is that considered a new generation of yeast?  If so, about how many generations (or cycles?) can I do this, considering my sanitation is good?

Several generations of yeast cells are created every time a culture is propagated.  However, we can conveniently think of each subculturing event as a generation. 

There are no hard and fast rules with respect to how many generations a yeast culture can be subcultured.  A yeast culture may remain stable for as little a couple of generations or as long as thousands of generations.  I often suggest that people who want to maintain a liquid culture do so until it starts to exhibit a decline in performance.  Yeast culture performance decline usually occurs over more than one generation.

If a brewer repitches a culture long enough, it will adjust to his/her brew house.  Many house strains started out as a common strain and became house strains through mutation.  The house culture that Ipswich was using back in the nineties started out as Wyeast 1028.  I do not know if they are still using the same house culture.

[denny]

so "as long as the gravity is low" and "wont be making alcohol"....not sure i get that. low OG still makes alcohol, no? how low we talking about.

Brewing yeast can both respire (requires presence of fee oxygen) and ferment (which does not).  However, even in the presence of oxygen, yeast will ferment rather than respire if there is sufficient glucose present (the Crabtree effect).

I've seen different figures listed for the glucose threshold, including 0.3%, 0.4% and 0.5% w/v.   

You just made me realize I mistyped the number!  .5% is what I've heard.

[majorvices]

Depends on how you make your starter. If you keep them in the respiratory stage then it does not count as a gen. If you make a simple, unstirred/unaerated starter then that counts as one gen.

Least, that's how I understand it.

Yeast do not respire in the presence of glucose levels above the Crabtree threshold.  All beer worts, even 1.020 starters, are above the Crabtree threshold.  All growth above the Crabtree threshold is fermentative growth. However, in the presence of dissolved O2, a small amount of glucose is shunted to the respiratory metabolic pathway for the synthesization of ergosterol and unsaturated fatty acids.

Thank you for factualizing my comments!

[reverseapachemaster]

how many times would one consider this a good practice before you want to move on to a fresh vial of yeast?

The typical answer is 5-10 generations, but if the sanitation is good and it's still performing consistently, I'll go longer. I think in Yeast they recommend 5 generations.

On White Labs' homebrewing side of their website they recommend five generations as a good stopping point but at least at one time the craft brewing side recommended up to fifteen pitches.

[majorvices]

A friend of mine who worked at Harpoon said they go 50 gens on their yeast but of course they do heavy lab work. I generally go 5-7 maybe 10. It is easy to see when the yeast start to act differently. The first thing I notice is a difficulty to clear the beer even after fining.

[thebigbaker]

A friend of mine who worked at Harpoon said they go 50 gens on their yeast but of course they do heavy lab work. I generally go 5-7 maybe 10. It is easy to see when the yeast start to act differently. The first thing I notice is a difficulty to clear the beer even after fining.

My first 5 turned out well and I'm currently fermenting the 6th, so we'll see how this one turns out.  As far as active fermentation, there really was no difference (at least w/ the eye test) from the 1st to the 6th. 

Sounds like this might be a good topic for an article in Zymurgy, that is if there hasn't already been one. 

[S. cerevisiae]

A friend of mine who worked at Harpoon said they go 50 gens on their yeast but of course they do heavy lab work. I generally go 5-7 maybe 10. It is easy to see when the yeast start to act differently. The first thing I notice is a difficulty to clear the beer even after fining.

They've also more than likely selected an isolate that remains relatively stable under their brewing conditions.  I have that culture on slant.  I plated it from a bottle of Harpoon UFO.  It's in the culture tube labeled "HAR" in the photo shown below.

[erockrph]

A friend of mine who worked at Harpoon said they go 50 gens on their yeast but of course they do heavy lab work. I generally go 5-7 maybe 10. It is easy to see when the yeast start to act differently. The first thing I notice is a difficulty to clear the beer even after fining.

They've also more than likely selected an isolate that remains relatively stable under their brewing conditions.  I have that culture on slant.  I plated it from a bottle of Harpoon UFO.  It's in the culture tube labeled "HAR" in the photo shown below.

Are you sure the UFO strain is the same as their core beers? Their core beers taste like London Ale to me, but I've always suspected that the UFO line was a different strain.