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
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!
I received a question about the irrigation technique I mentioned and I wanted to elaborate a bit.
The amount of irrigation water required depends on the soil (drainage) and the crop level so there is not a clear amount per vine or per acre that will reduce the alcohol by 0.1%. This type of "addition" is inherently imprecise and relies on experience. It's typically done within a few days of harvesting, so it does not affect ripening. The intention is to reverse a loss of water due to dehydration, not to dilute the fruit. Alcohol will typically be adjusted only by a fraction of a percent.
The benefit of this technique is that it feels more natural, it allows winemakers to say they're not adding anything, and gives the plant and fruit the opportunity to react (adjust concentrations of other components) in a way that adding water to a tank does not.
Hi Jennifer, interesting point and thanks so much for your valuable contribution. Thankfully for this MW question, this technique would not need to be mentioned, as it was a winemaking rather than viti exam paper. In the final exams you probably have time to mention 5 key points and write around 1000 words (this answer is far more extensive) so you'd need to consider what's most important to the particular question. You might also find the work of John Forrest in Marlborough, NZ, very interesting if lowering potential alcohol in the vineyard is of interest. He has spent years identifying the major sugar-producing leaves on the vine and removing them from the plant at key times in the season to produce wines that have full flavour ripeness and similar acid profile but with 6 brix less than conventionally farmed vines. His label The Doctors is the result.