The challenge of higher alcohol levels in wine, with special reference to Chateauneuf du Pape.

A 2019 Cairanne Southern Rhone from my cellar with a quite typical 15.5% alcohol

The Institut Rhodanien has comprehensively reviewed the changing maturation of Grenache in Southern Rhone since 1969 and demonstrated that potential alcohol has increased by 2.7%, total acidity has decreased by 1-95 grams per litre and grape weight has reduced. There are two factors at work here. First, when temperatures are high, that part of the ripening process which sees reducing acidity and increasing sugar levels can outstrip the ripening of skins and stalks (phenolic ripeness) necessary to avoid green vegetative flavours and unripe tannins. The grower is then faced with a dilemma – if (s)he waits for the phenolic ripeness to reach acceptable levels the sugar levels may be so high that if the fermentation is allowed to use all the sugars (ie to produce a dry wine) the alcohol levels may be too high. A little rain in the ripening period may serve to reduce the sugar ripeness and allow the phenolic ripeness to catch up, but global warming has also upset previous more predictable rainfall patterns which now seem to alternate more frequently between extremes of deficit and excess.  

Higher alcohol levels present a challenge on multiple levels. The first is that they can make the wine unbalanced, as noted above. Because higher sugar (and thus potential alcohol levels) are accompanied by lower acidity the wine can be both too hot, and, flabby. A lack of acidity can be mitigated by adding acid (usually tartaric) in the winemaking process and this has become quite commonplace in hotter wine producing regions. Carefully done, this may help bring a higher alcohol wine back into balance – but added tartaric can also impart an undesirable “hardness” to the wine.

But even if balance at higher alcohol levels is achieved, higher alcohol levels present other challenges. So the second issue relates to wine cost: in numerous regimes tax is levied based on alcohol levels. For example, if a wine is above 14% alcohol in the US, the winery has to pay 50% more tax. Similarly in the UK, from February 2025, duty on wine has been based on alcohol strength.

The third issue, and presumably what underlies the differential tax rates, is the impact of alcohol consumption on health. We’ll ignore the WHO claim that there is no safe level of alcohol consumption which is NOT based on the current scientific evidence and focus instead on the more reasonable and typical national health recommendations for moderation which are typically that men should not consume more than 14 units per week spread over at least three and preferably not more than five days per week. Now if you were to drink 7 x 150ml glasses a week of wine at 13% alcohol by volume (ABV) you’d be comfortably below 14 units per week. If you drank the same amount of wine at 14.5% ABV you’d be over that guideline.

So higher alcohol levels in wine present challenges for sensory perception, for cost, and for health. How are winemakers dealing with these challenges?

First of all, for the serious winemaker, issues of wine quality and sensory perception will trump everything else. It may be cheaper and healthier for the consumer if wines stay below 14% but we are not going to see premium Chateauneuf du Pape with alcohol levels below 14%!

The wine begins in the vineyard so this is where the quest for balanced wines and acceptable alcohol levels also begins.  Elevation and aspect – where choices are possible – can make a huge difference with higher elevations and less direct sun slowing sugar buildup, retaining acidity and allowing more time for phenolic ripeness. Canopy management is also important – striking the right balance in leaf removal to encourage phenolic maturity whilst providing shading to slow sugar ripening. The soils on which vines are planted have an impact, sandy soils being less moisture retentive may allow sugar ripeness without phenolic ripeness in dry years whereas soils with limestone or clay may assist to keep sugar and phenolic ripeness in step.   Finally, managing yields is also important: the crop thinning once seen as desirable to ensure good concentration may now need to be moderated to ensure sugar ripeness does not speed away.

Varietal choice and blending can be important. The Southern Rhone backbone is Grenache. Grenache is well adapted to hot climates – but it comes with the price of higher sugars and thus higher alcohols.  Syrah, typically the number two player in the blend is slower to accumulate sugar so increasing the Syrah percentage may be seen as an option. However, Syrah is less well adapted to hotter climates, tending to lose its aromatic quality and deliver jammy fruit. Grenache does seem to have an ability to soak up high alcohol levels without losing the freshness of its fruit.

Some other red grapes can reach phenolic ripeness at lower sugar levels and these might be incorporated – Mourvedre and Counoise meeting these criteria in the permitted Chateauneuf varieties, albeit starkly different. Another trend is to blend small amounts of white varieties like Clairette or Bourbolenc into the reds, which deliver higher natural acidity, lower sugars, freshness, and aromatic life to help balance the naturally high alcohol of Grenache. Beyond simply blending, some growers are co-planting and co-fermenting the white grapes with the reds which delivers better integration of flavours, whilst softening alcohol perception and preserving colour.

Winemaking interventions can have a significant impact. The more traditional and conservative interventions include cooler fermentation temperatures (especially) to help retain bright fruit and aromatic life, using open-top fermenters which allow some alcohol to evaporate and selection of yeast. We have mentioned above acidification by judicious addition of tartaric.

There are two primary methods for taking alcohol out of the wine once made. The first is reverse osmosis (RO) . In this method some of the wine is pushed past a semi-permeable membrane through which the water and alcohol pass leaving behind the other wine components (the retentate) . The water and alcohol are then distilled to separate the alcohol from the water (the alcohol evaporates at a lower temperature. The water is then recombined with the retentate and in turn that is then blended back with the remaining wine to achieve an ABV lower than the original.

Diagram of Reverse osmosis for alcohol reduction in wine

The second method is spinning cone technology. Widely used now to produce no-alcohol wine this features a tall vertical cylinder with alternating stationary and spinning cones operating under vacuum conditions allowing low-temperature distillation to separate volatile compounds such as alcohol and aromas. The wine is gently warmed and introduced into the column where it flows over the spinning cones forming a thin film. Steam or nitrogen gas is then pumped into the column, lifting the volatile aromas which are collected and saved. The wine is then passed through the column again to evaporate the alcohol which is removed. The previously captured aromas are then re-introduced to the de-alcoholised wine.