There are many ways a winemaker can influence the final alcohol of wine before fermentation, during fermentation, and after fermentation. This essay will look at these three stages of the winemaking process, addressing the various methods that can be employed to increase or decrease the final alcohol level of a wine and why they might be considered useful. There are many reasons for a winemaker to alter the final alcohol level of a wine: to achieve a certain style of wine, to meet customer demands, for legal and taxation reasons, and for microbiological stability.
The decision to pick early may be made by a winemaker, particularly in warm regions, in order to minimize sugar levels and potential alcohol levels, as well as to retain acidity. Mauricio Lorca makes a Torrontés from La Rioja, Argentina, picking one parcel early and one parcel at full physiological ripeness and blending the two to balance alcohol levels. However, early picking to reduce potential alcohol levels is not always judicious, particularly with red wines, as it can result in unripe tannins and green flavors. In some hot climates where ripe grapes attain naturally high brix levels, water may be used to dilute the must. However, this technique increases the pH of the must, which negatively affects microbiological stability and dilutes concentration levels (though there are also winemaking techniques to mitigate these effects). While allowed in the US, Australia, and other regions, adding water is not permitted for wines sold in the European Union, with the exception of water used for the purpose of incorporating additives. Yet the total volume of water to wine for the addition of additives is as high as 7% in Australia, far more than is necessary, which could reduce alcohol by 1% ABV, if the full allowance were used.
Conversely, if grapes have attained low brix levels due
Adding water dilute BOTH sugar (decrease alcohol) and acidity (increase pH) equally wouldn't it?
Also adding tartaric acid is another method to control pH (decrease pH) to a small point (cannot add much as it will change the wine's profile and make-up).
Adding water dilutes the sugar and the acidity (and increases pH). Many winemakers add a small amount of acid along with the water to maintain juice acidity.
In addition to the previous question, I have another one on the yeast that you mentioned which supposedly 'reduces" some alcohol level. You have identified AWRi 796, Saccharomyces, but its description does not mention such function... Another one that you suggested which reduced abv for Shiraz and Chardonnay, I believe, was AWRI 1149, non Saccharo. But this yeast must be inoculated sequentially by Saccharo to have the effect, mustn't it? I just wanted to see if I am on the right track
Hi Rebecca. Thank you for easy to follow explanation on the subject. Just one thing I did not quite comprehend. You mentioned that 'watering down' must/juice "increases" the pH of the must. However, while water dilute acidity (which increases pH), it also dilute sugar as well. So wouldn't it remain at the same (high) pH (it started with)? Or watering down somehow dilute more acidity than sugar? Many thanks for your feedback in advance.
Rebecca, thanks for this very exhaustive article! One other technique for reducing alcohol that seems to be gaining in popularity is irrigating (where possible) just prior to harvest rather than adding water to the must. This gives the winemaker much less control than a water addition, but some feel better doing this than dumping buckets of water into the tank.
I'm curious about glucose oxidase. Do you have a sense for whether it's being used now, if it was mostly used in the past, or if it was always more of an academic concept (I found a few scientific papers on the topic but no commercially available enzyme from the typical winemaking suppliers)? It's difficult for me to imagine why a producer would choose to use this over the alternatives. Thank you!