Author Topic: Real Wort vs. Dextrose Yeast Starter | xBmt Results!  (Read 1179 times)

Offline brulosopher

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Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« on: June 06, 2015, 06:23:59 PM »
Contributor Greg Foster compared the differences between fermenting the same beer with a real wort starter vs. a starter made from corn sugar, something I've been very curious about. Results are in!

http://brulosophy.com/2015/06/05/real-wort-vs-dextrose-yeast-starter-exbeeriment-results/

Offline erockrph

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #1 on: June 06, 2015, 06:47:06 PM »
Your results make biological sense to me. It's not so much that cells lose the ability to produce enzymes over time, it's just that there are biological feedback loops that upregulate or downregulate the production of proteins. This takes time - it's not a quick process.

My guess is that yeast cells upregulate the production of maltose permease (the enzyme that brings maltose into the cell) and/or maltase (the enzyme that cleaves maltose into its constituent sugars) in response to increased maltose concentrations. In other words, if the yeast is in the presence of malt sugar it will take steps to increase its ability to use it.

Yeast grown in the absence of maltose are less likely to have a large amount of these enzymes. The genes that encode for the production of these enzymes are always present, they're just not always turned on. Once they are signaled to ramp up production it takes time to start churning out these enzymes. That would seem to explain the increased lag times and slower drop in gravity for the dextrose-starter beer.

What I was most interested in reading was that there was little difference in flavor between the two. I guess you could use another sugar source in a pinch if you really needed to boost cell count, but wort still seems like the best option. I have run into a situation where I was lower than expected on DME. I might consider boosting the starter with sugar if I ever run into that situation in the future.
Eric B.

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Offline narcout

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #2 on: June 06, 2015, 06:48:35 PM »
Are you in LA? 

I've never joined Pacific Gravity, but I can see that the meeting was at Culver City Homebrewing, which is my LHBS.
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Offline brewinhard

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #3 on: June 06, 2015, 06:59:19 PM »
Very cool report.  I love reading your xBmt's.  Keep'm coming! 

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #4 on: June 06, 2015, 07:04:00 PM »
I have been using a starter wort that is composed of 50% extra light DME/50% dextrose with a pinch of Fermax for quite some time.  I switched from using 5% w/v extra light DME to using MYGP as the medium that I use for making plates and slants last year.  I prepare my own MYGP, which consists of 0.3% w/v malt extract, 0.3% w/v yeast extract, 1.0% w/v glucose (dextrose), and 0.5% w/v peptone. I use a soy-based product called Soytone because of the threat of BSE (a.k.a. mad cow disease).  The prion that causes BSE is not denatured by autoclaving at 121C.

Offline brewinhard

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #5 on: June 06, 2015, 07:14:13 PM »
What benefits of this 50/50 blend have you observed to make you switch?  Cost, ease?

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #6 on: June 06, 2015, 07:53:28 PM »
The first time that I made a starter using 50% DME/50% dextrose was due to the fact that I was low on DME.  I continued to use the recipe with the addition of Fermax because it seems to produce a higher cell count per gram.  It's important to use Fermax or other nutrient that contains yeast extract (a.k.a. autolyzed yeast).  I pay close to the same price for a pound of dextrose as I do for a pound of DME, so it is not much of a cost savings. 

Briess Pilsen DME (what I use) has the following composition:

Glucose 13%
Maltose  48%
Maltotriose 14%
Higher Saccharides 19%

If we add 50% dextrose (assuming that the dextrose is pure glucose), the sugar composition is as follows:

Glucose 56.5%
Maltose  24%
Maltotriose 7%
Higher Saccharides 9.5%

It's not like the yeast cells do not have to transcribe the enzymes necessary to break apart the glycosidic bonds that hold maltose and maltotriose together.  It's just that they have a lot of glucose that they can utilize directly before they have to shift to reducing disaccharides and trisaccharides to glucose.  Additionally, the higher saccharides have been cut in half.  Most brewing yeast strains cannot reduce these sugars to glucose.  Adding Fermax boosts the free amino nitrogen level and provides vitamins and trace elements.

One last thing, as I have mentioned many times before, the dry yeast manufacturers propagate yeast using a fortified molasses-based medium.  Dry yeast does not see malt-based extract until it is pitched into a batch of wort. 
« Last Edit: June 07, 2015, 04:14:10 PM by S. cerevisiae »

Offline erockrph

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #7 on: June 07, 2015, 03:34:46 PM »
It would be interesting to see if there is a difference between sucrose (table sugar, a disaccharide) and dextrose (i.e., d-glucose, a monosaccharide). I don't bother keeping dextrose on hand because sucrose works just as well for my brewing needs up to this point.

It's not like the yeast cells do not have transcribe the enzymes necessary to break apart the glycosidic bonds that hold maltose and maltotriose together.  It's just that they have a lot of glucose that they can utilize directly before they have to shift to reducing disaccharides and trisaccharides to glucose.  Additionally, the higher saccharides have been cut in half.  Most brewing yeast strains cannot reduce these sugars to glucose.  Adding Fermax boosts the free amino nitrogen level and provides vitamins and trace elements.

That makes me wonder if a dextrose-boosted starter may be a better medium for at least the first step of a starter for yeast that may be in poor health (bottle dregs, old slurry, outdated/mishandled smackpack, etc.). This way it gets an initial boost of easily used sugar to get it going early, but still has some maltose in solution to get it ready for further steps into an all-malt fermnentation. I think I'll give this a try in the near future.
Eric B.

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #8 on: June 07, 2015, 04:27:33 PM »
It would be interesting to see if there is a difference between sucrose (table sugar, a disaccharide) and dextrose (i.e., d-glucose, a monosaccharide). I don't bother keeping dextrose on hand because sucrose works just as well for my brewing needs up to this point.

At some point, I would like to perform a true controlled study of dextrose fortified starter wort.  Even with a 5% w/v (1.020) solution, the amount glucose in pale DME is over twice that of the Crabtree threshold of 0.3% w/v; therefore, all reproduction is via the fermentative metabolic pathway.  Boosting the glucose percentage to 56.5% does not change that dynamic.

5 * 0.13 = 0.65% glucose w/v
5 * 0.565 = 2.285% glucose w/v

Edit: I meant to say "all reproduction is via the fermentative metabolic pathway," not "all reproduction is via the respirative metabolic pathway." 

« Last Edit: June 08, 2015, 12:24:39 AM by S. cerevisiae »

Offline brulosopher

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #9 on: June 07, 2015, 06:48:39 PM »

Are you in LA? 

I've never joined Pacific Gravity, but I can see that the meeting was at Culver City Homebrewing, which is my LHBS.
Greg is in Redondo Beach and is a PG member.

Very cool report.  I love reading your xBmt's.  Keep'm coming!
Thanks, will do!

I have been using a starter wort that is composed of 50% extra light DME/50% dextrose with a pinch of Fermax for quite some time.
This is great, I ought to try it out.

At some point, I would like to perform a true controlled study of dextrose fortified starter wort.  Even with a 5% w/v (1.020) solution, the amount glucose in pale DME is over twice that of the Crabtree threshold of 0.3% w/v; therefore, all reproduction is via the respirative metabolic pathway.  Boosting the glucose percentage to 56.5% does not change that dynamic.

5 * 0.13 = 0.65% glucose w/v
5 * 0.565 = 2.285% glucose w/v
I would love this!

Offline brewinhard

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #10 on: June 07, 2015, 07:26:33 PM »
One last thing, as I have mentioned many times before, the dry yeast manufacturers propagate yeast using a fortified molasses-based medium.  Dry yeast does not see malt-based extract until it is pitched into a batch of wort.

Including fermentis?  Does this enable some to be gluten free options?

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #11 on: June 08, 2015, 01:23:21 AM »
Yes, Fermentis propagates yeast using a molasses-based medium.  Fermentis and Lallemand both propagate yeast aerobically using a continuous process and a device known as a bioreactor.  This process is very different than way you, I, White Labs, Wyeast Labs, and most of the brewing world propagates yeast.  We use batch propagation where the glucose level exceeds the Crabtree threshold of 0.3% glucose w/v.  Above this threshold, the Crabtree effect kicks in.  The Crabtree effect causes yeast cells to favor reproduction via the fermentative metabolic pathway even in the presence of dissolved O2

Reproduction via the fermentative metabolic pathway is significantly less efficient than reproduction via the reparative metabolic pathway.  If we can hold the medium in a steady state below the Crabtree threshold, the Pastuer effect will kick in.  What happens when Pasteur effect kicks in is that the yeast cells convert pyruvate to acetyl CoA instead of ethanol.  Acetyl CoA is fed directly into something known as the TCA (Tricarboxylic Acid) or Krebs cycle where it is converted to energy. 

If we examine this process from a chemical point of view, it is easy to see that carbon is more effectively utilized in the respirative metabolic pathway than it is in the fermentative metabolic pathway. To keep things simple, let's just look at the major compounds that are formed.  Both metabolic pathways take in glucose, which has the chemical formula C6H12O6 (6 carbon atoms bound to 6 water molecules).  The major compounds produced by the respirative metabolic pathway are H2O and CO2.  The major compounds produced by the fermentative metabolic pathway are CH3CH2OH (a.k.a. ethanol) and CO2.  As one can plainly seen, ethanol is a carbon-based compound.  If a cell is excreting carbon, it is not using it for energy.

One last thing, yeast cells do not consume sugar.  They consume carbon.  Sugar is carbon bound to water.  All of the sugars found in wort are multiples of CH2O.  The simplest sugars are called hexoses because they contain 6 carbon atoms.  Hexoses are monosaccharides.  An interesting thing happens when two hexoses combine to form a disaccharide.  A water molecule is lost.  This loss forms something known as a glycosidic bond, which is a type of covalent bond.  While the chemical formula for glucose is C6H12O2.  The chemical formula for maltose, which consists of two glucose molecules bound by a glycosidic bond is not C12H24O12.  It is C12H22O11.  A yeast cell splits maltose into two glucose molecules by transcribing1 an enzyme that inserts a water molecule; hence, the term hydrolysis.  Hydrolysis is the combination of "hydro" (water) and "lysis" (break apart). Hydrolysis means to break apart via the insertion of water.   The formal name for mashing is the hydrolysis of starch.

[1] For curious, transcription is the process by which an organism's genes encode proteins. Enzymes are proteins.

Offline dak0415

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Re: Real Wort vs. Dextrose Yeast Starter | xBmt Results!
« Reply #12 on: June 08, 2015, 12:45:19 PM »
I can't find the post right now, but I seem to remember that Tom Schmidlin stated that S. Cerevisiae do not lose the ability to use maltose with sucrose as the starter, as they do with dextrose.
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