Jeff Grossman
Jeff Grossman
In the Prince of Pinot article, Kevin Harvey says the rose petal thing comes from whole berry fermentation.
The one-two Givry-Chablis punch
- Thread starter Rahsaan
- Start date
Oswaldo Costa
Oswaldo Costa
Apologies, mon ami!
Thought about this issue a lot yesterday and sent some questions to a winemaker friend who uses whole cluster in conventional fermentation.
Things I asked for his opinion about:
Does he think the church side of the spice spectrum comes from the stems or from the 2% abv of intracelular/enzymatic fermentation that happens before the skins burst?
Does intracellular begin the moment a whole cluster is clipped from the vine?
If a winemaker were to not crush his whole clusters on the same day he picks (does this ever happen, and why?), how long might it take for them to ferment enzymatically up to the 2% abv level?
Will report back when he answers, but an interesting thing he has already said is that in enzymatic intracellular fermentation, it is malic acid that is converted to alcohol, not sugar. He also said, and this touches on Fla Jim's question and Mark's response, that carbonic is anaerobic, while semi-carbonic is aerobic, so the yeasts will find a way to ferment sugar, with or without acetobacters, in either environment.
Jeff Grossman
Jeff Grossman
Hm.
I doubt malic acid is fermentable.
I know you don't need acetobacter to ferment. Acetobacter is a bacterium, not a yeast, and its action is a second, separate process that, in the presence of oxygen, converts ethanol into acetic acid.
The whole reason that yeast ferment/respire is to convert sugar into energy. The first step in the process is glycolysis, the breaking-apart of the sugar. Every one glucose molecule gives you two molecules of pyruvic acid. And now we come to the fork in the road:
== If oxygen is present, then pyruvic acid turns into acetyl coenzyme A (which is then munged by the Krebs Cycle to become energy).
== If oxygen is not present then pyruvic acid comes to another fork in the road:
*** If the fermentation is taking place in a plant, then pyruvic acid becomes acetaldehyde first and then ethanol.
*** If the fermentation is taking place in an animal (deep inside a muscle, say), then pyruvic acid becomes lactate, a form of lactic acid; eventually, when blood circulation pumps the lactic acid away, the liver finishes the processing.
Jeff Grossman
Jeff Grossman
With some more reading: There are various bacteria that convert malic into lactic. Some of them only do that, while some run multiple reactions. Some like oxygen, some don't, and some can do a bit of each.
There are several found in wine. Most of them seem to be responsible for off-flavors and off-aromas of various kinds. The desirable one -- the one that winemakers inoculate with -- is named Oenococcus Oeni. O. Oeni is a hetero-fermenter (multiple products) and a facultative anerobe (prefers anerobic but can deal with some oxygen).
O. Oeni gets energy by converting a molecule of malic acid into a molecule of lactic acid (and, in the process, freeing up a molecule of CO2 and a proton). It also can digest sugar; its end-products are either ethanol (if not much oxygen around) or acetate (if oxygen is around).
I'm going to stop there because it gets dizzying after this: there are many kinds of sugars and many strains of bacteria and they spit out a wide variety of chemicals that, themselves, feed into other processes. Most of which end badly, by the way: ammonia, haze, VA, etc.
All of which is to say, to MLippy: yes, malic acid is fermentable, if you think there is O. oeni inside a grape before it is crushed.
Florida Jim
Florida Jim
Or if you inoculate with it.
Best, jim
Oswaldo Costa
Oswaldo Costa
Malic acid converted by enzymes into ethanol at the beginning of the winemaking process, and converted by bacteria into lactic acid towards the end, are different processes, but I don't know enough chemistry to defend the reality of the first.
Oswaldo Costa
Oswaldo Costa
Malic acid contained in the grapes is degraded 20-50% and transformed into ethanol.
I gave the reference to Jamie Goode's article, which does discuss the anaerobic conversion of malate to ethanol in grapes. Here's the relevant part excerpted:
When whole bunches of grapes are placed in an atmosphere of carbon dioxide, they take it up and use it in anaerobic fermentation. In this process they break down sugars, but also malic acid, which is one of the main acids present in grapes. This malate degradation is the most significant step taking place during anaerobic fermentation, and it’s broken down sequentially to pyruvate, acetaldehyde and then ethanol. Typically, at a fermentation temperature of 35 °C, half of the malic acid is degraded in this way.
Mark Lipton
p.s. The conversion of malate to ethanol involves decarboxylation to lactate, oxidation to pyruvate, decarboxylation (thiamine-mediated) to acetaldehyde and reduction to ethanol. I can mock up a reaction scheme if anyone wants to see it.
When whole bunches of grapes are placed in an atmosphere of carbon dioxide, they take it up and use it in anaerobic fermentation. In this process they break down sugars, but also malic acid, which is one of the main acids present in grapes. This malate degradation is the most significant step taking place during anaerobic fermentation, and it’s broken down sequentially to pyruvate, acetaldehyde and then ethanol. Typically, at a fermentation temperature of 35 °C, half of the malic acid is degraded in this way.
Mark Lipton
p.s. The conversion of malate to ethanol involves decarboxylation to lactate, oxidation to pyruvate, decarboxylation (thiamine-mediated) to acetaldehyde and reduction to ethanol. I can mock up a reaction scheme if anyone wants to see it.
Jeff Grossman
Jeff Grossman
Yes, please, because how is that oxidation step happening in a CO2-rich environment?
OK, I'll embed it as a GIF. Oxidation occurs biochemically using redox cycling and the cofactors NAD(P)/NAD(p)H and FAD/FADH. Since there's both an oxidation and a reduction step in the pathway, there's no cofactor depletion. This is a very common strategy and can be seen in e.g. the Krebs cycle.
Mark Lipton
Oswaldo Costa
Oswaldo Costa
Sexy locker-room talk.
Here are the four enzymatic steps involved:
malate dehydrogenase
pyruvate dehydrogenase complex
acetaldehyde dehydrogenase (run backwards here)
alcohol dehydrogenase (also run backwards)
Mark Lipton (ChemBoy)
malate dehydrogenase
pyruvate dehydrogenase complex
acetaldehyde dehydrogenase (run backwards here)
alcohol dehydrogenase (also run backwards)
Mark Lipton (ChemBoy)
Oswaldo Costa
Oswaldo Costa
Would be useful if we could distinguish the aroma/flavor effect of those first 2% of enzymatic abv from the aroma/flavor impact of stem contact during the subsequent yeast fermentation.
Oswaldo Costa
Oswaldo Costa
"NP-complete problems are often addressed by using heuristic methods and approximation algorithms."
Steve Guattery
Steve Guattery
The key word is "often". It's not clear that it's possible to find a good approximation algorithm for certain NP-complete problems such as the Travelling Salesman Problem (TSP). It's been proven that if you did find one, you'd prove P=NP. (There is a good approximation algorithm for TSP instances in which the triangle inequality holds, however.)
I'm not sure what NP-completeness has to do with the chemistry of fermentation, but I thought I'd share a little geekery related to reduction in a different sense.
Jeff Grossman
Jeff Grossman
Wasn't it proven that all NP-complete problems are the same as cover-set?
Oswaldo Costa
Oswaldo Costa
Heuristically-speaking, I remember a visit to Sébastien David in Saint Nicolas (described in a Loire report from 2010) in which we tasted a peculiar (and pelicular) cuvée named Kézako, made using destemmed but uncrushed grapes inside barrels that are rotated every few days to mix the contents. This would be a rare (to my knowledge unique) example of intracellular without subsequent stem contact, although, since the grapes no longer have their peduncles, some yeast must find its way into the whole berries. In any case, this cuvée tastes super carbonic. Possible evidence that the middle eastern spices come from enzymatic processes.
Ian Fitzsimmons
Ian Fitzsimmons
Puzzling over the term 'intra-cellular fermentation.' Literally, this means fermentation within the cell, right? How do the metabolizing organisms wend their way inside the grape cells? This seems like it would be more of a virus-y thing.
Perhaps, however, the term is used loosely to indicate fermentation within the grape, rather than its constituent cells; where bacteria, having penetrated the skin (through breakage or, say, stem holes) attack and break down the grape cells as substrate.
Browsing Goode's article (admittedly rapidly), he seems to be saying that there is a graduated sequence of fermentation processes in these conditions, where free oxygen circulation is impeded or interdicted. The initial 'intracellular' fermentation is dominated by non-yeast microbes, which use the abundant CO2 molecules to oxidize this substrate (including malic acid, from damaged/preyed-upon grape cells). When the alcoholic byproduct of this slow initial metabolic process reaches about 2%, the grape cells die, their juice is released, and large-scale sugar fermentation proceeds, thenceforth dominated by yeast (until the yeast population pollutes itself out of existence).
A relevant point would be that in this nuanced, multi-phase system, small variations in initial conditions could disproportionately affect the specifics of average, aggregated metabolic reactions at each phase, as well as the corresponding abundances of their products; which is to day, small changes in procedure may cause significant changes in the chemical composition of the final solution. I think this is, in fact, what we observe in the various wines of, say, Beaujolais, even within a single appellation.
An illustration of this idea could be that full-cluster processing, by keeping most of the grapes' stem holes plugged, significantly slows the rate of bacterial invasion of grapes' interiors, and thus of initial 'intracellular' fermentation. in this case, perhaps more grape cells would die of starvation than of bacterial assault, prior to the kick-in of yeast-dominated fermentation. The flavor contribution of bacterial waste products to the final blend would be much smaller then for a de-stemmed batch. In addition, the migration of polyphenols from grape skin inwards would be diminished, as well as ethanol production and the related production of esters giving berry aromas (stipulated - I'm leaning very heavily on Dr. Goode's description here).
In this imagining, the exclusion of oxygen in the initial stages of fermentation in vinification could play a role analogous to that of cooling dough in sourdough bread making - i.e., of promoting non-yeast microbial activity, thereby enhancing its contribution to the final flavor package.
Anyway, blah, blah, blah. I patiently await, and preemptively accept, in full, Mark Lipton's devastating critique and correction of these conjectures.
Perhaps, however, the term is used loosely to indicate fermentation within the grape, rather than its constituent cells; where bacteria, having penetrated the skin (through breakage or, say, stem holes) attack and break down the grape cells as substrate.
Browsing Goode's article (admittedly rapidly), he seems to be saying that there is a graduated sequence of fermentation processes in these conditions, where free oxygen circulation is impeded or interdicted. The initial 'intracellular' fermentation is dominated by non-yeast microbes, which use the abundant CO2 molecules to oxidize this substrate (including malic acid, from damaged/preyed-upon grape cells). When the alcoholic byproduct of this slow initial metabolic process reaches about 2%, the grape cells die, their juice is released, and large-scale sugar fermentation proceeds, thenceforth dominated by yeast (until the yeast population pollutes itself out of existence).
A relevant point would be that in this nuanced, multi-phase system, small variations in initial conditions could disproportionately affect the specifics of average, aggregated metabolic reactions at each phase, as well as the corresponding abundances of their products; which is to day, small changes in procedure may cause significant changes in the chemical composition of the final solution. I think this is, in fact, what we observe in the various wines of, say, Beaujolais, even within a single appellation.
An illustration of this idea could be that full-cluster processing, by keeping most of the grapes' stem holes plugged, significantly slows the rate of bacterial invasion of grapes' interiors, and thus of initial 'intracellular' fermentation. in this case, perhaps more grape cells would die of starvation than of bacterial assault, prior to the kick-in of yeast-dominated fermentation. The flavor contribution of bacterial waste products to the final blend would be much smaller then for a de-stemmed batch. In addition, the migration of polyphenols from grape skin inwards would be diminished, as well as ethanol production and the related production of esters giving berry aromas (stipulated - I'm leaning very heavily on Dr. Goode's description here).
In this imagining, the exclusion of oxygen in the initial stages of fermentation in vinification could play a role analogous to that of cooling dough in sourdough bread making - i.e., of promoting non-yeast microbial activity, thereby enhancing its contribution to the final flavor package.
Anyway, blah, blah, blah. I patiently await, and preemptively accept, in full, Mark Lipton's devastating critique and correction of these conjectures.