Flor Question for Winemakers

originally posted by MLipton:
originally posted by John DeFiore:

"Flor yeasts partially respire ethanol, glycerol, acetic and veral organic acids, producing acetaldehyde and various aromatic metabolic by-products"
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John (and others),
In the midst of an otherwise clear passage, the word veral perplexes me. Can you please help this poor, confused organic chemist understand what that word might mean in this context?

Mark Lipton
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You're an organic chemist and you've never heard of veral organic acids?

Actually, after looking back at the book what it means is that I was typing too quickly without reading what I was typing and somehow typed "veral" instead of "several".

But you do have to be careful of combining veral organic acids with prefamulated amulite because you could create unstable volatitic proteites.

John
 
Such deep, intellectually stimulating exchanges are what makes this bored so addictive in the forlorn southwestern corner of Europe.
 
See, the thing I like about this board is the likelihood that, at any given moment, someone is posting something incredibly douchey for absolutely no reason. As someone who may have done the same once or...um, twice...I find it comforting.
 
originally posted by VS:
Here's what Eduardo Ojeda of Valdespino tells me through Alvaro Girón, the 'third man' in Equipo Navazos:

"There are indeed sherries with a high concentration of acetaldehyde, while others have less, and this depends exclusively on the strain of yeast in the butt, which has undergone a procedure of selection and adaptation over a long time.

The production of acetaldehyde does not occur, as the question seems to imply, by sheer oxidative action, but through the action of metabolism in a reductive environment. The wine finds itself in such an environment because the yeast veil needs and consumes both the oxygen that's dissolved in it and the oxygen in the part of the butt with air. This makes the airing of the wine (the 'corrido de escalas', or moving younger sherries into butts containing older sherries) necessary, so that the yeast can be fed and the metabolic processes prolonged.

In that metabolism, expressing it in a simple way, the yeast consumes acetic acid and ethanol. There are complex biochemical cycles which explain it more correctly, but I'm not an expert. It seems simple but it's hard to understand, since the natural way of producing acetaldehyde by oxidation consumes ethanol and increases acetic acid."

Alvaro adds that the question asked seems to leave the biological dimension of the flor action aside. He has consulted Justo Casas' 2008 book, 'La vinificación en Jerez en el siglo XX' (Vinification in Jerez in the 20th century) and extracted some quotes:

"Everything seems to indicate that the redox potential of wine in the aging butt depends on the degree of activity of the flor yeast at that time of the year. To us, it's obvious that wine aging under a flor veil is not an oxidative process. In fact, the wine is in a reduced state."

"The literature says that the flor veil acts as a screen or a sheet that's impermeable to gases and impedes the physical access of oxygen to the wine. It's hard to agree with this viewpoint, as it's not been demonstrated. I rather think that the yeasts in the veil catch the oxygen in the immediate atmosphere and use it to breathe or to oxidize the ethylic alcohol or acetaldehyde, so that the oxygen molecule in contact with the veil or next to it disappears. This seems to be the most logical reason why the veil is largely impermeable to the passage of oxygen."

"Until today ethanol has been quoted as the only component of wine which oxidizes during the aging under flor. It does so through the enzymatic action of the flor yeast in an extremely specific action, with no alteration of the other wine components which might intervene in what we could call the oxidation of wine."

"We see that, at the same time as the oxidation of alcohol produces acetaldehyde, reductive substances and ions are produced. Part of those will continue their normal metabolic routes until combining with the oxygen in the air that is in contact with the yeast cells in the upper part of the veil, while another part of them carry out their reductive action on the wine components, which explains why the oxidation of ethanol into acetaldehyde simultaneously produces wine in a reduced state, as shown by measures of its redox potential."

"In conclusion, if the intensity of the sharp character of fino sherry depends mainly on its concentration in acetaldehydes, its softness to the nose and in the mouth, which good tasters particularly appreciate, is related, in my opinion, to the level of reduction in the wine, of which we can get an idea through its redox potential, also shown through its naturally paler color."

Alvaro, on his part, concludes: "There's a generalized resistance to considering finos and manzanillas as fundamentally non-oxidative wines. You change your mind quickly the first time you smell a butt in which the flor is working intensely: the reduction stench is not pleasant at all!"

[Slightly edited to improve my clumsy English translation.]
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This only serves to reinforce my longstanding policy of being extremely selective in deciding which butts to smell.
 
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