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The Significance of Alcohol in Wine Production
- Alcohols are predominantly produced by yeasts during yeast fermentation, with ethanol being the main alcohol produced.
- It is important to know the wine's alcohol concentration levels for the following reasons -
- Wine labels are required to state the alcohol concentration of the wine to meet both domestic and export legal requirements.
The concentration is usually stated as a percentage of the volume (of alcohol) per volume (of wine) (%v/v) or Alc/Vol.
- In Australia, the number of standard drinks contained in a bottle of wine is also a label requirement.
This is calculated from the alcohol concentration.
"Aprox. 7.7 Standard drinks", is an example of standard drinks labeling for a 750 ml bottle of wine with 13%v/v alcohol content.
- To confirm predicted alcohol concentration levels, calculated from grape sugar determinations.
- To monitor changing alcohol concentration levels, during long term cooperage.
- To calculate the final alcohol concentration after blending wines of different alcoholic strengths.
- To confirm the concentration of alcohol, following fortification.
- For educational and training purposes
For the palate to be able to distinguish between different alcohol concentration levels requires practice, especially if other wine components such as sugar and parameters such as temperature are aspects that potentially interfere with or mask the perception of alcohol.
- Next to water, alcohol, by volume, is the next major wine component, with ethanol being the main alcohol.
- Ethanol has no taste and virtually no flavour, however, ethanol does create a sweet sensation in the mouth and adds body to wine due to its viscosity, which is greater than water.
- Alcohol is the main carrier of aroma and bouquet and hence flavours of wine.
- Alcohol provides balance to a wine. Remove the alcohol from a wine and notice the difference.
Likewise, high alcohol wines require increased flavour concentrations and body to carry and balance the higher alcohol concentrations
At the extreme end, fortified wines usual require increased sugar concentrations to carry and balance the high alcohol concentration.
- At high concentrations, ethanol produces a feeling of heat in the mouth that can almost be painful at the extreme end of the spectrum.
- An increase in temperature will make ethanol more evident in a wine.
The converse is also true, with wineries serving fortified Muscat wines straight out of the freezer, as a summer drink, in a similar way that Schnapps can be served from the freezer to reduce the hot sensation of alcohol.
- Wines produced from grapes grown in warmer climates have the capacity to accumulate higher levels of sugar and hence higher levels of alcohol and in turn bigger wines.
- Alcohol, as brandy spirit or SVR, can also be added to wine to fortify a wine. (e.g. port, sherry or mistela).
Whether low strength brandy spirit is used, with complex flavour components, or the high strength, non-diluting, neutral SVR spirit is used, depends on the style aimed for.
- The fortification of wine is still a practice that utilizes alcohol's preservative and sterilizing properties.
Yeasts suffocate in their own waste product (alcohol), with most wine yeasts only able to survive in alcohol levels below 15% v/v.
Bacteria, pathogenic to humans, do not survive the harsh environment of wine. Alcohol is one of the contributing components to this inhospitable environment.
It used to be thought that no bacteria could survive at the very high levels of alcohol in wine (17-21 % v/v), however certain species of LAB bacteria have known to survive, producing mousy (as in mouse cage) off flavours as a by product.
These undesirable flavour compounds are produced when these bacteria consume sugars that are present as part of the fortified wine style.
To prevent the growth and activity of these bacteria, high levels of sulphur dioxide (SO2) are employed in stored wines, to protect those valuable, aged, blending stocks.
- Yeasts produce other alcohols, besides ethanol, in minor quantities, but with important flavour implications (see alcohols in wine).
- Alcohols found in wine are all able to form both temporary and more permanent flavour compounds called esters by combining with the organic acids in wine.
- The tri-alcohol, glycerol, has a very high viscosity, but unless the grapes were heavily affected by botrytis, little glycerol is found in wine for it to significantly contribute to wines' viscosity.
- Methanol, methyll alcohol or wood alcohol can be produced by yeast during fermentation at levels of 0.1g/L (0.01 %v/v).
Most of the methanol in wine is derived from grape pectins with the highest levels found in red wines because of the extended maceration on skins.
It is the alcohol well known for causing blindness or even death when concentrated to toxic levels, through distillation.
- Alcohol acts as a solvent, extracting grape skin components such as tannins, including colour pigments.
As the alcohol concentration increases during fermentation the extraction of skin components increases, with implications for the timing of pressing red wine musts.
- It is alcohol that is responsible for the phenomenon referred to as the "tears" or "legs" of wine (see explanation).
- Alcohol, apart from all its contributing factors refered to above, is also an intoxicating agent.
Therefore the following adages are good advice -
- Drink wine in moderation.
- Booze less, be at your best.
- Drink, drive, idiot
- Drink better, drink less. Life is to short to be drinking bad wine.