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Offline DonBrown

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Wine alchol content - question
« on: 12/08/2008 14:51:03 »
On holiday recently I bought a bottle of Italian wine. The label contained the item
"Alcole effetivo 7,5%vol - Alcole totale 10,5%vol"
I have always assumed that the only significant alcohol in wine is ethanol and that this is what "affects" me when I drink it.  Now I'm wondering what the other 3% is.
The wine was a little sweet, so I wonder if sugar is an alcohol? (I'm not an expert, but there do seem to be a few =c-oh and even ch2oh groups floating around in glucose & fructose.)
Any chemist or wine buff (or even, Italian wine buff chemist) who can clarify?



 

Offline Bored chemist

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Wine alchol content - question
« Reply #1 on: 12/08/2008 19:08:45 »
Technically sugar is an alcohol- so's antifreeze, but it's an odd way to express the sugar content of a wine.
Also, an alcohol content of just 7.5 or 10.5% isn't very high so I wonder why the yeast stopped fermenting the stuff if there was still all that sugar left.
Usually wine ferments until the sugar runs out or the alcohol kills the yeast.
One psiiblilty that occurs to me is that one is the estimated alcohol based on the original sugar content of the grape juice (or based on the density) and the other is a true, measured, alcohol content.
I think this document
www.aiscanavese.it/.../cartella-amministrativa/la-normativa-dell-etichetta-vini-i-g-t/vini-ad-igt.pdf -
might shed some light on this but my knowledge of Italian is at about the level of "Ciao Bellissima". Can anyone help?
Drat; just tried that link and it doesn't work.

OK google "alcole totale" and look at the 6th result
« Last Edit: 12/08/2008 19:34:18 by Bored chemist »
 

Offline Make it Lady

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Wine alchol content - question
« Reply #2 on: 12/08/2008 19:25:23 »
I can only vaguely remember my mum and brother making wine together in the 70s. I think that you could stop the fermentation process when the wine was reluctant to stop fermenting and/or you wanted a sweeter wine. If this was a sweet wine then perhaps it had been stopped in this way leaving some of the sugar as a none fermented ingredient.
I will see if I still have the book "wine making for Beginners." which was sold at Boots the Chemist, purveyor of wine making equipment. It may explain things and I'll post again.
 

Offline RD

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Wine alchol content - question
« Reply #3 on: 12/08/2008 19:55:08 »
On holiday recently I bought a bottle of Italian wine. The label contained the item
"Alcole effetivo 7,5%vol - Alcole totale 10,5%vol"

The 7.5% and 10.5% figures are close to alcohol by weight (ABW) and alcohol by volume (ABV).

Quote
To convert ABW to ABV we take our ABW and divide by the density of ethyl alcohol (0.79)
http://www.ratebeer.com/Story.asp?StoryID=547

So 7.5% ABW = 9.49% ABV 
 

Offline Bored chemist

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Wine alchol content - question
« Reply #4 on: 12/08/2008 20:55:48 »
True, but it's not as close as I'd expect; 9.5% isn't 10.5% (Either the tax man or the consumer would be ripped off) and anyway, both values are said to be % by volume.
 

Offline RD

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Wine alchol content - question
« Reply #5 on: 13/08/2008 09:06:12 »
True, but it's not as close as I'd expect; 9.5% isn't 10.5%
Either the tax man or the consumer would be ripped off) and anyway, both values are said to be % by volume.


If Don had consumed the contents of the bottle his recollection may not be accurate :)
 

Offline DonBrown

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Wine alchol content - question
« Reply #6 on: 13/08/2008 11:12:12 »
Thanks for all the ideas. I can add a few details:

"If Don had consumed the contents of the bottle his recollection may not be accurate" - I drank only about 2/3 of the bottle, but that certainly was "effetivo" enough for me.  However, I kept the bottle and have it in front of me now, so the quote of the label is accurate.

"... an alcohol content of just 7.5 or 10.5% isn't very high so I wonder why the yeast stopped fermenting the stuff if there was still all that sugar left.  Usually wine ferments until the sugar runs out or the alcohol kills the yeast."
-Indeed so.  This is Lambrusco - Vino Frizzante. In the UK Lambrusco is often labelled as "partially fermented grape must (or juice)". It is commonly available here as a relatively low alcohol party drink. That is 3.5 - 4%, but IMO rather too sweet.  If you can find it, Lambrusco around 8% alc is only slightly sweet and much better balanced.
I don't know how they stop the fermentation - I would guess by Pasteurisation, by filtering or by sulphiting.
I found this quote on a winemakers website:
"The grapes are picked by hand, usually at the beginning of October, then immediately pressed. The partial alcoholic fermentation of the sugars is stopped when the right sugar content is reached through different filtrations. After months of aging, the fresh fruit juices are put into tanks for the natural fermentation process that gives San Guiseppe Lambrusco its signature delicate sparkle."
This might be a particularly upmarket wine, as I found several refences saying that the "frizante" is produced by injecting CO2.

"...making wine together in the 70s. I think that you could stop the fermentation process when the wine was reluctant to stop fermenting and/or you wanted a sweeter wine. "
My recollection of winemaking is that they always stopped *before* I wanted them to! I wanted the alcohol! If I wanted sweeter, I'd just add more sugar.
To make Port style wines, they add alcohol (brandy, I think) to stop the fermentation while there is unfermented sugar - giving a strong, sweet wine (15%+).

 

Offline Make it Lady

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Wine alchol content - question
« Reply #7 on: 13/08/2008 11:46:53 »
You were unlucky. My Mum's batches would bubble away for ever. She liked her wine a little sweet so would stop it. Can't find the book though, might be up in the attic. Adding a little alcohol from elsewhere does ring a bell though. I was only about 9 at the time though.

I also remember a lot of camdem tablets floating about which I think were used to sterilise stuff.
« Last Edit: 13/08/2008 11:48:57 by Make it Lady »
 

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Wine alchol content - question
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