Global temperatures are rising due to climate change, accelerating the growth of wine grapes accordingly. Warmer winters have caused grape budbreak to occur earlier, and through increasingly hot summers, we can now harvest grapes that are more mature than ever before. While this might sound promising, winemaking operations are increasingly finding themselves struggling with this seemingly positive development.
The culprit is the rise in wine alcohol content caused by grape over-ripening.
The Reality of Earlier Harvest Times
Riesling is generally known as a late-ripening grape variety. While it can grow in cool climates, it requires a long period to reach full maturity, which is why in Germany, where I live, harvest typically begins in mid-October.
However, in recent years, seeing such maturation levels in mid-September has been nothing short of astonishing. Even more surprising was that the must sugar levels of Riesling harvested in September had already reached Auslese class.
Auslese class generally represents a maturity level that can be considered fully ripe. Riesling of this class is typically made into sweet wines. This is because complete fermentation would result in alcohol levels exceeding 13%. While 13% alcohol is ideal when making powerful red wines, for delicate dry Riesling wines that showcase acidity and fruitiness, this alcohol level approaches the upper limit.
Furthermore, the problem with this year's grapes is that despite such high sugar levels, other aspects of ripeness have not yet caught up in many cases.
Unable to Wait for Non-Sugar Ripeness
In June 2019, at the AOC Bordeaux general assembly in France, the planting of grape varieties that had not previously been permitted was approved. The reason was the necessity of responding to climate change.
All these movements stem from the same fundamental problem.
In winemaking, grape sugar content is not the only requirement. The amount of acids contained, tannins, and the harmony of flavors created by these elements are all necessary. However, recent temperature increases due to climate change cause sugar levels to rise disproportionately quickly among these elements, while dramatically reducing acid levels.
Rising sugar levels equate to rising alcohol levels.
If harvest timing is moved earlier due to concerns about sugar content in grape juice, the resulting wine will have insufficient flavor and give a strong impression of being unripe and green. On the other hand, if harvest is delayed to achieve proper flavor development, grape must sugar levels rise too high, resulting in excessively high alcohol content and equally unbalanced wine.
The timing window for properly capturing the middle ground between these two extremes has become extremely narrow, or may have already disappeared entirely.
This is why Bordeaux's approach involves planting grape varieties that are better adapted to hotter climates as a countermeasure.
Efforts to Reduce Alcohol Content
Once grapes have ripened, it is impossible to return them to an unripe state.
However, the rise in wine alcohol content due to grape over-ripening has become an urgent issue, and extensive research is being actively conducted on solutions. Several techniques have already been implemented and are beginning to be used in winemaking operations.
Methods using spinning cones and reverse osmosis fall into this category, but these techniques and their required equipment are large-scale and costly. However, there is actually a method that can be implemented much more simply than these approaches.
That method is water addition to juice before fermentation.
If something is too concentrated, dilute it—this is an extremely simple approach that anyone could conceive. Precisely because it is simple and universally conceivable, it is also a technique that has already been devised and implemented throughout history.
As a result, in modern winemaking operations, water addition has become something of a forbidden technique.
Water Addition Prohibited by Law
While there are many research cases regarding alcohol adjustment techniques using spinning cones and reverse osmosis, surprisingly little research has been conducted on diluting grape juice by adding water. The reason is that water addition to grape juice is prohibited under EU wine law and the wine laws of many other countries.
The reason many countries' wine laws prohibit water addition to grape juice is to regulate the watering down and production of counterfeit wines that occurred in the past. Due to the experience of legitimate wines being pressured by such counterfeits entering the market, legal provisions were established in the early 1900s stating that "beverages that are not alcoholic fermentation of fresh grapes or grape juice shall not be sold under the name wine" (Kensuke Ebihara, "Wine Law," Kodansha).
Against this background, research was likely considered unnecessary because it was clearly prohibited by law.
However, this situation is now beginning to change.
Regulatory changes by the Food Standards Australia New Zealand have made it possible to add water to grape juice before fermentation to adjust sugar levels, provided certain conditions are met. In response to this, research results on the effects of adding water to grape juice before fermentation were reported in 2020, centered at the University of Adelaide.
The Winemaking Significance of Alcohol Adjustment Through Water Addition
When adjusting alcohol content by adding water, the most important factor is that this be done before fermentation. If water is added after fermentation is complete and the product has become genuine wine, while the alcohol content will certainly decrease, the flavor will also become diluted.
At the same time, risks such as microbial contamination through water also increase, potentially affecting wine quality.
Looking at the experimental results in the aforementioned research paper "Substitution or Dilution? Assessing Pre-Fermentative Water Implementation to Produce Lower Alcohol Shiraz Wines," whether through juice replacement with water or simple dilution by water addition, various parameters that would likely affect wine quality and sensory evaluation showed changes compared to cases without water addition. This is naturally expected since water is being added to the juice.
The question is whether these changes can be tolerated.
The experimental results published in the paper reported decreases in phenolic compounds and tannin levels, so when water is added to juice before fermentation, the finished wine will have lighter color and reduced astringency. Regarding taste, fructose concentration also decreases, so sweetness perceived in the mouth will be weaker, while acid levels show no significant change.
Taking these factors together, one can imagine the result would be a wine with a relatively acidic, fresh, and light character.
However, these are results from reducing original alcohol levels of 13.6% or 15.5% to around 11% or 12%.
A wine with 15% alcohol requires the presence of substantial tannins and sugars that provide a full-bodied mouthfeel, but for wines with 11% or 12% alcohol, such elements could conversely cause imbalance. In this sense, alcohol adjustment through water addition can also play a role in balancing the flavor of the finished wine.
Summary | Could Water Addition Become an Essential Technology?
As already discussed, adding water to grape juice before fermentation is currently legally prohibited in many countries.
However, regarding the major problem facing modern winemaking—rising alcohol content due to climate change—there is no other countermeasure as simple and accessible as this approach. It would not be surprising if countries and regions worldwide eventually begin permitting this method.
Of course, permitting water addition to grape juice comes with many problems.
Adding water to juice is, as history has proven, precisely the act of "watering down," and could lead to mass production of inferior products. There would also be taxation regulations, and whether wine quality can truly be guaranteed remains debatable. The question of whether it is acceptable to add chlorinated tap water cannot be ignored either.
For consumers, if this were perceived as "watered-down" wine, significant image damage would be unavoidable. These are paths we have already traveled once before.
If such techniques were permitted, there would inevitably be those who would wait until grapes are over-ripe despite accepting some yield reduction, then mass-produce by diluting that juice with water. How can this be regulated? How can we avoid repeating history?
While adding water to juice is very simple as a technique, the path to its implementation is far from simple. Nevertheless, I believe it will eventually be adopted in winemaking operations worldwide.
That is how significant a challenge alcohol content management has become in modern times.
