Author Topic: A couple questions on starters  (Read 1839 times)

Online mabrungard

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Re: A couple questions on starters
« Reply #15 on: December 03, 2010, 12:51:14 PM »
Kai has an interesting approach, but I'm concerned with the foaming and loss of yeast volume. 

On page 130 of White & Zainasheff's Yeast book, there is a story that illustrates the number of yeast cells in foam.  Its hard to determine the true yeast numbers in the foam from the story, but it implies to me that there was a huge number sequestered in the foam since the cell count went from 6 million to 35 million per mL after the foam was mixed in. 

Blowing off foam is OK for beer making, but its too valuable when making starters.
Martin B
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Offline Kaiser

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Re: A couple questions on starters
« Reply #16 on: December 03, 2010, 01:08:17 PM »
Kai has an interesting approach, but I'm concerned with the foaming and loss of yeast volume.

The yeast loss is minimal in lagers. This is a different story for ales. I cannot propagate the latter that way and for those I use a 2l flask on a stir plate.

Kai

Offline dak0415

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Re: A couple questions on starters
« Reply #17 on: December 03, 2010, 02:03:06 PM »
I would think that you could just insert an air tube into the small side of a carboy cap (the 6.5 gal caps fit a 2L flask, the 5 gal caps fit 4000 and 6000ml flasks) and blow filtered air onto the surface of the starter wort.  That will mix things up and tend to displace the CO2 so more O2 would be available to the yeast coming to the surface.  You could also try submerging the end of the tube and just allow a slow flow into the wort, that should alleviate most of the foaming problems caused by stones.

My $.02
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Offline tschmidlin

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Re: A couple questions on starters
« Reply #18 on: December 04, 2010, 01:12:31 AM »
Catabolite repression is caused by glucose, not maltose, and our worts are primarily maltose.  However, maltose is converted to glucose (but not in the presence of glucose), so if the rate of that conversion is high enough maybe it could trigger the Crabtree effect.  Maybe conversion is so fast that even 100% maltose will still trigger it in brewing strains?  Typical brewing strains are likely to more maltase than standard lab strains, which typically come from bread making.  This is good to keep in mind with any published research.

The Crabtree threshold will also be dependent on the expression of various enzymes that will tend to push it toward the TCA cycle instead of fermentation.  So it seems to me the threshold can be strain dependent even within brewing strains.

Anyway, I don't have access to the primary research (and it's in Polish), but it was reported by DeDeken (1966) that Slonimski (1956) puts the level of glucose at 6 mM.  That's ~1g/l, or 1.0004.  Also in 1956 Ephrussi et al reported that 3% glucose (SG = 1.012) triggers the Crabtree effect.

As far as I know, we still don't understand exactly what causes the catabolite repression, meaning what pathway does the level of glucose trigger that causes aerobic fermentation.  But for what it's worth, standard lab yeast growth media uses 2% glucose (SG = 1.008). I asked my PI years ago why 2% and if that avoided the Crabtree effect.  He didn't know what I was talking about, just shrugged and said that's what is standard.  :-\
Tom Schmidlin

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Re: A couple questions on starters
« Reply #19 on: December 04, 2010, 05:46:12 AM »
I'm curious.  Would lager foam contain the same quantity of yeast cells as ale foam when measured on a weight basis?  In other words, does a gram of lager foam have a similar cell count as a gram of ale foam? 

As Kai wrote, I would assume that a top-cropping ale yeast would more typically produce a foam stand than a bottom-cropping lager yeast.  But, is that always true?  If it is true, then I can agree that yeast cell losses from a lager starter are lower.
 
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Offline ipaguy

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Re: A couple questions on starters
« Reply #20 on: December 04, 2010, 06:12:19 AM »
Nice photo of Kai's setup.  I'm not sure, but I think the air tube is routed up through the inside of the blowoff  tube and into the carboy.  Looks applicable to a primary fermenter, as well as for starters.  Just run the pump for an hours or so after pitching.  I like this setup because you can get as much O2 into the wort as you want without worry about poisoning the yeast from overuse of pure O2.
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Offline Kaiser

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Re: A couple questions on starters
« Reply #21 on: December 04, 2010, 04:57:37 PM »
Ipaguy, yes the airline is routed through the blow-off hose. I also weigh down the aquarium air stone with a stainless steel nut.

Martin, lager kraeusen contains way less yeast than ale Kraeusen. The hydrophobicity and formation of branched colonies causes ale yeast cells to rise into the Kraeusen.

Kai

Offline thcipriani

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Re: A couple questions on starters
« Reply #22 on: December 05, 2010, 12:04:51 AM »
I actually asked Chris White about starter gravity right before the new yeast book came out - I was surprised to see the book espousing JZ's oft quoted 1.030-1.040 starter after having received this response from Dr. White:
Quote
To really eliminate the crabtree effect, you need to be down under 1.010, and slowly feed the yeast sugar.  But 1.025-30 is still a good range, and I think it is a good compromise to good yeast physiology and good fermentation.  So I think that is the best gravity

Also, Kai, have you ever considered something like this as a cheap alternative to conical propagation:
http://www.midwestsupplies.com/fermentap.html
Tyler Cipriani
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Offline tom

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Re: A couple questions on starters
« Reply #23 on: December 05, 2010, 10:59:39 AM »
Kai, Why don't you like to use a foam control product?


AFAIK all the yeast suppliers culture at <1°P (1.004) to avoid the Crabtree Effect entirely. The only reason that isn't a viable approach (pardon the pun) for most brewers is that you need to be able to add precise quantities of wort, and remove precise quantities of alcohol, continually through the entire culturing phase.

It is my understanding as well that the Crabtree Effect already becomes effective at fairly low gravities. 1.020 is already too high. However, like Sean pointed it out, there is a practicality aspect to the starter wort gravity. Too high and the yeast gets stressed too much and too low and you’ll need large starter volumes.

In addition to that, in an aerated environment, oxygen is not the growth limiting factor. At least in brewer’s wort it is nitrogen and you may have to add nitrogen to the wort to reap the benefit of the more yeast growth when you manage to suppress the Crabtree Effect enough that the the yeast actually starts to metabolize sugars aerobically.
All we want in our starters is for the yeast to build up as many sterol reserved as they can by supplying unlimited amounts of oxygen. Unless we can handle very low gravity worts I doubt that we can prevent them from fermenting the sugars.

For a while now I’m propagating my lager yeast like this:



The Carboy contains 10-12l of 2 Plato wort and is constantly aerated with an aquarium pump through and air stone. I don’t like using foam control which is why I blow off excess foam into a pot. The aeration provides a constant movement in the starter beer which helps in keeping the yeast in suspension. I have been able to raise very well performing yeast with this set-up but recent measurements of the new growth per gram of extract showed less than 1 Billion/g which is not as good as the results that I get on a stir plate. There I can get 1.3-1.6 Billion/g.

If I had a conical I’d love to give this set-up a try:


Yeast harvesting in this set-up would be much easier.

But this is a subject that interests me very much and we should keep discussing this. Maybe we can find a conclusive answer to the question regarding Crabtree Effect and the wort gravity at which is starts.

Kai

Brew on

Offline Kaiser

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Re: A couple questions on starters
« Reply #24 on: December 06, 2010, 02:00:54 PM »
Kai, Why don't you like to use a foam control product?

I just don't need it. Just like I don't think Whirlfloc/Irish moss are needed.

I try to be a purist when it comes to brewing and don't like to add more than what's needed unless there is a real benefit. But we have discussed the issue of foam control before and nobody could bring the argument of adverse effects on beer foam which would be the primary concern about using this product.

Kai