How do "dormant" yeast interact with the beer?

[CrystallineEntity]

It's a scientific Showdown!!!!

 

[boss429]

To leave the cake or not leave the cake that is the question..haha good stuff though I wish i could follow and give an opinion..

btw ray g what are your qualifications? just curious

 

[-TH-]

I've never before been so entertained and yet felt so dumb all at the same time.

 

[ajdelange]

It's a scientific Showdown!!!!

It's common for there to be disagreements between scientists (and I'm not one, BTW). There are ways to resolve these but egos sometimes get in the way. For example, on perhaps the simplest point in this discussion: the change in oxidation state of a carbonyl carbon when it is "reduced" to an alcohol, e.g. HCHO + 2H ---> CH3(OH), there are "rules" by which the oxidation state can be determined. The ones promulgated by the IUPAC (an international body that sees to such things for chemists) are quite simple to the point that I can paste them in here:

* * * * *
"Oxidation State

A measure of the degree of oxidation of an atom in a substance. It is defined as the charge an atom might be imagined to have when electrons are counted according to an agreed-upon set of rules: (l) the oxidation state of a free element (uncombined element) is zero; (2) for a simple (monatomic) ion, the oxidation state is equal to the net charge on the ion; (3) hydrogen has an oxidation state of 1 and oxygen has an oxidation state of -2 when they are present in most compounds. (Exceptions to this are that hydrogen has an oxidation state of -1 in hydrides of active metals, e.g. LiH, and oxygen has an oxidation state of -1 in peroxides, e.g. H2O2; (4) the algebraic sum of oxidation states of all atoms in a neutral molecule must be zero, while in ions the algebraic sum of the oxidation states of the constituent atoms must be equal to the charge on the ion. For example, the oxidation states of sulfur in H2S, S8 (elementary sulfur), SO2, SO3, and H2SO4 are, respectively: -2, 0, +4, +6 and +6. The higher the oxidation state of a given atom, the greater is its degree of oxidation; the lower the oxidation state, the greater is its degree of reduction."

* * * *


I would encourage each of you to apply these rules to the simple reaction above and see what you think the oxidation states are in the formaldehyde (left side) and methanol on the right side. Actually I'll do it for you as it's so simple and you can check my work if you like. In the formaldehyde (HCHO) there are two hydrogens (oxidation state +1 each according to the rules) and 1 oxygen (-2) according to the rules. The sum over all the atoms must be 0 so the oxidation state of carbon must be 0. In the methanol, CH3(OH), there are 4 hydrogens (+4) and one oxygen (-2) so the carbon must have an oxidation state of -2 because +4 -2 -2 = 0. The oxidation state of the carbon has been changed from +2 to 0, a reduction of 2. Refer again to the rules for hydrogen. The hydrogen atoms on the left each have an oxidation state of 0. On the right they have an oxidation state of +1 each. Thus the carbonyl alcohol has incurred reduction by 2 and the hydrogens oxidation by 1 each for a total of 2 and everyone should be happy. Matching oxidation and reduction to get chemical equations balanced is one of the main reasons for doing all this.

Now if you don't like that answer there are 2 approaches you can take. The more constructive one is to say "Gee, there's a discrepancy here between what the IUPAC rules give and what I compute. Why is that?" and that's what a good scientist does. The other is to simply declare the IUPAC rules and any textbook that uses them as wrong or, worse still, to accuse your faithful reporter of doctoring what he copied and pasted from the IUPAC website for the sake of winning an argument. This sort of thing, unfortunately, does happen, but is, fortunately, typically limited to those on opposite sides of the global climate change debate.

But the IUPAC rules are not wrong. The rules for assignment of oxidation number are, to quote one text "somewhat arbitrary" and the phrase "agreed-upon" in the IUPAC definition implies that. If my correspondent does not wish to subscribe to the IUPAC rules that's fine but he should, in that case, state whose rules he is following and what they are. It may be that in his industry a different set of rules are used. As an example of this, the "standard conditions" for redox potentials are different for biochemists than chemists of other stripe. In such a case a reasonable scientist says "There's the discrepancy! You are using IUPAC rules but in the YYY field we use the XXX rules." To say "IUPAC is wrong" is an unfortunate response because not only is it antiproductive but it tends to destroy the credibility of the one making such a statement.

For full disclosure: when I calculated the change in oxidation state earlier I used a slightly different, but consistent, set of rules (which you can find in chemistry textbooks or at http://www.newworldencyclopedia.org/entry/Oxidation_state where the IUPAC rules are also stated - look under "From a Lewis structure"). They give the same result but that doesn't necessarily mean that all sets of rules should.

I swore I wouldn't take any more flame bait here but I didn't realize others were following. I'm certainly happy that I was able to provide some entertainment and hope that anyone who has been following along will do his own research and come to his own conclusions.

 

[pjj2ba]

........ As an example of this, the "standard conditions" for redox potentials are different for biochemists than chemists of other stripe. ............

As I was reading the thread, this was my exact thought as to the source of the disagreement

I swore I wouldn't take any more flame bait here but I didn't realize others were following. I'm certainly happy that I was able to provide some entertainment and hope that anyone who has been following along will do his own research and come to his own conclusions.

Thanks for the entertainment! For what it is worth, I'd have to say I found no flaws in your statements. I have taken quite a few advanced biochemistry classes (it has been a few years though). I've also conducted my fair share of enzyme assays but am mostly doing DNA/RNA stuff lately, so my hard core biochem. is a little rusty. My organic chemistry is much rustier.



Also, I have a pdf copy of Understanding Alkalinity and Hardness pt II and I love it! It got me into using lime to reduce my temporary hardness. This made a big change in smoothing out the bitterness of my beers. Thank you!!!!

The one thing I've always been curious to know, and keep meaning to test, is just how quickly will the temporary hardness come to equilibrium with CO2 in the air? I keep mulling this over in my head. If I bubbled air through a tank of water (say 10 gal) how quickly with it come to equilibrium (and remove a good chunk of the temporary hardness)? My ideal situation would be to have a large water tank with a spigot that I'd fill with water, bubble for a week or whatever, then drain off what I need for a batch, and then just top off and keep on bubbling. My understanding is that this is the same as removing hardness by boiling. All the boiling does is to speed up the reaction. So if one were patient enough, could one just put air bubbler on and wait?

ps. I 'd be tempted to first run the air through a water trap to help keep evaporation to a minimum.

 

[ajdelange]

The one thing I've always been curious to know, and keep meaning to test, is just how quickly will the temporary hardness come to equilibrium with CO2 in the air? I keep mulling this over in my head. If I bubbled air through a tank of water (say 10 gal) how quickly with it come to equilibrium (and remove a good chunk of the temporary hardness)? My ideal situation would be to have a large water tank with a spigot that I'd fill with water, bubble for a week or whatever, then drain off what I need for a batch, and then just top off and keep on bubbling. My understanding is that this is the same as removing hardness by boiling. All the boiling does is to speed up the reaction. So if one were patient enough, could one just put air bubbler on and wait?

Slowly! We (as respiring creatures) wouldn't be able to regulate blood pH by CO2 exchange were it not for an enzyme (so this isn't that far OT), carbonic anhydrase which speeds the dissolution thousand fold (or more - that's just a guess). If I do add chalk to water to create an authentic profile I bubble pure CO2 through and it often takes 24 hr or more to get all the chalk dissolved.

But this probably isn't the best way to remove alkalinity. As the air scrubs out CO2 lime will precipitate and ultimately the mix will come to the CO2/carbonic/bicarbonate/lime equilibrium which is determined by air CO2 content. That's about 8 something pH and there can be a fair amount of alkalinity in the water at that level. The way to do this is to sparge with air but at higher temperature where the CO2 is less soluble, more leaves, and more CaCO3 precipitates. This is of course the standard way of decarbonating. You don't even have to bring it to a boil as long as you are sparging with air. The reason you need to boil if you don't is so that steam bubbles can do the sparging job.

 

[Cipper]

Yesterday's was my last.

Regards.

So you actually broke up with him before he broke up with you?

Chris

 

[ajdelange]

...there can be a fair amount of alkalinity in the water at that level.

I should have gone on to say that this residual level is about what you'd get by boiling or lime treatment i.e. you will get decarbonated to about the same extent if you are willing to wait. Perhaps a twist on this is that water that is reasonably super saturated wrt CaCO3 may not form a precipitate at all or so slowly that it effectively stays super saturated. Adding some finely divided chalk to provide nucleation sites may help in this situation.

 

[ajdelange]

To leave the cake or not leave the cake that is the question.

In all the arcana I guess that question didn't really get answered. You want the beer to have low ORP (oxidation reduction potential) so that 1) existing carbonyl carbons (diacetyl, acetaldehyde) will be reduced and 2) no reduced (saturated) carbons get oxidized (to trans 2 nonenal or other manifestations of staling). The other thing you want is low pH.

The basic reduction reaction is

R(CO)R1 + NADH + H+ --> R(HCOH)R1 + NAD+

R and R1 stand for the rest of the molecules. You want CO converted to HCOH (i.e the carbon reduced). CO is what's responsible for the nasty taste/smell of acetaldehyde (and any other aldehyde) and diacetyl (and other VDK's). Even though diacetyl contains 2 carbonyl groups (the second one is part of R1), reducing either one reduces the strength of the objectionable flavor dramatically. So you want the reaction to procede to the right. LeChatelier's principal says that you do that by increasing the concentration of one or more of the reactants (on the left) and/or decreasing the concentration of one or more of the products (on the right). Active yeast do both. They:

1) produce acid (H+ ~ low pH)
2) produce NADH and
3) produce the NADH from NAD+.

Thus you want yeast present. The question is when and for how long. The following comments are based on lagers where diacetyl seems to be more of a bete noir than in ales.


Diacetyl not produced by yeast. The yeast form acetolactate and that gets non enzymatically oxidixed to diacetyl which must be reduced. So how long you keep the beer on the yeast depends on how you plan to manage diacetyl. In the Narziß method, the yeast are pitched cold and the temperature is allowed to rise slowly during the ferment. At the conclusion the temperature is raised, for a day or 2 accelerating the formation of diacetyl from acetolactate and the beer is then lagered, on the yeast, for a relatively brief period after which it can be racked or filtered off. Good for a commercial brewer.

In the traditional method the pitch is at a higher temperature (but still below 50 °F) and is not raised at the end so much less acetolactate is converted. Instead of that taking place over a day or two the conversion, and subsequent reduction, take place over the months of traditional lagering. At that time the beer is transferred off the yeast and packaged. It is also diacetyl (and acetaldehyde) free and relatively stable.

If you can keep the beer on the yeast, which as a home brewer, you can, beyond the lagering period you can keep the beer fresh for a year or more. Eventually, however, the yeast do give up the ghost and diacetyl begins to be noticeable again.

Last nite we were comparing my Boh Pils (done the traditional way) to the local GB guy's (obviously done the Narziß way because a commercial operation cannot afford the long lagering time). Very similar beers - equally free of diacetyl anyway.

An interesting third method has now emerged in the form of a product called Maturex. This is the enzyme acetolactate decarboxylase which takes acetolactate directly to acetoin thus bypassing the oxidation to diacetyl and subsequent reduction by the yeast. This means no raised temperature step (diacetyl rest) and very short lagering are possible (just long enough to establish low ORP and clean up acetaldehyde). Very good for commercial brewers.

 

[rayg]

Diacetyl not produced by yeast. The yeast form acetolactate and that gets non enzymatically oxidixed to diacetyl which must be reduced.

Diacetyl is certainly produced by yeast. The reaction of acetoin to
diacetyl is reversible that's why the enzymes that do that have
two names in the KEGG database:

(R,R)-butanediol dehydrogenase;diacetyl reductase [EC:1.1.1.303]

and

diacetyl reductase [(S)-acetoin forming];(S)-acetoin dehydrogenase [EC: 1.1.1.304]
(see http://www.genome.jp/kegg/pathway/map/map00650.html
top center)

The pH inside the cell is not the same as the pH of the wort, so
it's not a good idea to relate wort chemistry to cell metabolism.

Ray

 

[ajdelange]

Those who wish to understand the mechanisms by which diacetyl is formed in brewing may wish to consult Takashi Inoue's (Dr. Diacetyl) "Diacetyl in Fermented Foods and Beverages"
avaialble from the ASBC or Amazon: http://www.amazon.com/dp/1881696154/?tag=skimlinks_replacement-20

 

[ajdelange]

I just remembered something that may be of practical value to readers WRT diacetyl. Since it is formed non-enzymatically in the beer, not in the yeast, there is a simple test you can do to tell you when you can take the beer off the yeast. It involves heating a sample of the beer which speeds the decomposition of alpha acetolactate into diacetyl. In a nutshell, if heating a sample of the beer increases the diacetyl aroma then there is residual AAL in the beer and you should leave the beer on the yeast until all AAL is converted to diacetyl and the yeast have absorbed (and reduced) that diacetyl.

This was first brought to my attention years ago by George de Piro - former pharmaceutical chemist, homebrewer and now head brewer at C. H. Evans in Albany, NY who posted it to HBD way back when. So I did a search on de Piro and diacetyl and found this website http://www.professorbeer.com/articles/diacetyl.html where he describes the simple (no lab gear) procedure in some detail and gives instructions on how to interpret the results.

PS: Just tried this with the Kölsch I have in the fermenter right now and was planning to transfer tomorrow. I passed with flying colors so I'm ready to roll!