2009 Pepe Cerasuolo

My understanding, and again this is relatively lay, but I have been making wine for (all of) the last 7 weeks...

H2S the biproduct of a stressed (oxygen-starved, and thus "reductive") fermentations. It's an (autolytic?) bi-product of the yeast when they don't have enough oxygen to easily perform fermentation.

From personal experience I can say that I've done punchdowns on a few funky, stinky fermentations and that simply a longer punchdown seems to "feed" them and by the next punchdown the reductive aromas have (mostly) blown off. I've been working mostly with Merlot, a little Malbec and Tempranillo. The Syrah and Cabernet Sauvignon isn't ripe yet...

VS, Eric T., any input on this?
 
Err, am I wrong in thinking that oxygen isn't a prerequisite for alcoholic fermentation (which I always think of as anaerobic)?

I thought H2S formation was due to low-nitrogen musts.
 
originally posted by Yixin:

I thought H2S formation was due to low-nitrogen musts.
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See Bruce's comments above.

Though there is more than one way to make stinky, reductive wine.
 
SFJoe and Lisa are drawing molecules again. She gets me hot, with her molecules, the way she wraps her lips around those long chemical names.

CC
 
originally posted by Jeff Grossman:
SFJoe and Lisa are drawing molecules again. She gets me hot, with her molecules, the way she wraps her lips around those long chemical names.

CC
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Those were the days. Sorry I missed them.
 
originally posted by Yixin:
Err, am I wrong in thinking that oxygen isn't a prerequisite for alcoholic fermentation (which I always think of as anaerobic)?

I thought H2S formation was due to low-nitrogen musts.
Click to expand...

From what I read, this sounds ballpark: fermentation is a metabolic process that forgoes final reduction of oxygen at the end of the electron transport chain, which characterizes respiration, and is energetically more efficient.

Referring, per Joe, to Bruce's post, if H2S is an intermediary to amino acid formation, then uptake of this intermediary into the yest cell substance would be regulated, I guess, by the rate of formation of the final amino acids, which, in turn, would be limited by nitrogen availability, since nitrogen is an essential ingredient.

So if the H2S formation outruns amino acid formation, because nitrogen is scarce, then the excess H2S could be released as smelly gas, or possibly remain dissolved in the must. I guess you could expect excessive H2S production to peak as the yeast cells cease to multiply and begin to die back, when the rate of amino acid formation would fall rapidly.

Perhaps the presence of oxygen promotes yeast growth indirectly by removing fermentation by-products the pollute the yeast's immediate habitat and inhibit their reproduction.
 
H2S is not food, it's poop.

If yeast don't have enough nitrogen to assemble their DNA and proteins and so on, they eat amino acids to get it. When they eat the sulfur-containing amino acids, they discard the sulfur bits, often as smellies.
 
Okay; I was thinking about the paper I linked to yesterday, which referred to H2S as an intermediate in biosynthesis of sulfer-creating amino acids (methionine?). You and Bruce emphasized S release during amino acid break-down, which would occur more frequently, at least.

N abundance in a fermenting vat will depend on its availability in the grape material, and so could well limit yeast cell growth (if the yeast don't exhaust their carbon substrate or self-poison first). But I guess you are saying that, if S is released en route when the yeast break down the grape amino acids, in order to get at such nutrients as N, then N limitation is superfluous in explaining H2S formation. N limitation came to mind, however, because Yixin mentioned N-poor musts.
 
originally posted by Ian Fitzsimmons:

N abundance in a fermenting vat will depend on its availability in the grape material, and so could well limit yeast cell growth (if the yeast don't exhaust their carbon substrate or self-poison first). But I guess you are saying that, if S is released en route when the yeast break down the grape amino acids, in order to get at such nutrients as N, then N limitation is superfluous in explaining H2S formation. N limitation came to mind, however, because Yixin mentioned N-poor musts.
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Huh? The only circumstance when yeast (or any other organism) will catabolize amino acids to obtain N is when the organism has an N limited diet. What SFJoe has said is that catabolism of sulfur-containing amino acids is a source of H2S, so I see no inconsistency in those statements.

Mark Lipton
 
I also saw no inconsistency, and that's why I agreed with him. As I read his last post, though, amino acid catabolism in response to an N-limited diet is precisely what he described ("If yeast don't have enough nitrogen to assemble their DNA and proteins and so on, they eat amino acids to get it.").

If the catabolized amino acids happen to contain sulfer, the sulfer is released as waste, I gather (although it seems that some must be retained for anabolism of the yeasts' own sulfer-containing amino acids; hence perhaps the reference to H2S as an intermediary in the linked paper). The connection to nitrogen-poor must suggested by Yixin, I suppose, would be that N scarcity would enhance the rate at which the yeast break down amino acids and, therefore, the rate of S release.
 
originally posted by Ian Fitzsimmons:
I also saw no inconsistency, and that's why I agreed with him.
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OK. On a related note, some of Miller's data was recently re-examined and evidence for the formation of methionine found (DOI: 10.1073/PNAS1019191108).

Mark Lipton
 
originally posted by Ian Fitzsimmons:
I also saw no inconsistency, and that's why I agreed with him. As I read his last post, though, amino acid catabolism in response to an N-limited diet is precisely what he described ("If yeast don't have enough nitrogen to assemble their DNA and proteins and so on, they eat amino acids to get it.").

If the catabolized amino acids happen to contain sulfer, the sulfer is released as waste, I gather (although it seems that some must be retained for anabolism of the yeasts' own sulfer-containing amino acids; hence perhaps the reference to H2S as an intermediary in the linked paper). The connection to nitrogen-poor must suggested by Yixin, I suppose, would be that N scarcity would enhance the rate at which the yeast break down amino acids and, therefore, the rate of S release.
Click to expand...
Not to belabor, but H2S would probably not be the preferred anabolic intermediate. It's hard to control and very toxic.
 
originally posted by SFJoe:
originally posted by Ian Fitzsimmons:
I also saw no inconsistency, and that's why I agreed with him. As I read his last post, though, amino acid catabolism in response to an N-limited diet is precisely what he described ("If yeast don't have enough nitrogen to assemble their DNA and proteins and so on, they eat amino acids to get it.").

If the catabolized amino acids happen to contain sulfer, the sulfer is released as waste, I gather (although it seems that some must be retained for anabolism of the yeasts' own sulfer-containing amino acids; hence perhaps the reference to H2S as an intermediary in the linked paper). The connection to nitrogen-poor must suggested by Yixin, I suppose, would be that N scarcity would enhance the rate at which the yeast break down amino acids and, therefore, the rate of S release.
Click to expand...
Not to belabor, but H2S would probably not be the preferred anabolic intermediate. It's hard to control and very toxic.
Click to expand...

I'll try to read the whole paper over the weekend and make better sense of the author's characterization. Possibly small amounts of S are recaptured as needed from the ambient waste, and 'intermediate' is meant loosely.
 
So another bottle of the Pepe was much the same. A cleaned-up old copper penny helped some, but not enough.

Wonder if this is typical of other vintages of this wine.
 
The topic of reduction came up on another board, and one of the responses linked to this interesting article by Jamie Goode.

As a bonus, there's a longish bit at the end on possible enhancement of reduction and thiol formation under screwcap closure.
 
originally posted by SFJoe:
So another bottle of the Pepe was much the same. A cleaned-up old copper penny helped some, but not enough.

Wonder if this is typical of other vintages of this wine.
Click to expand...

Back, ye slayer of HOPE!
(I didn't need to hear this)
 
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