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Rising alcohol levels in wine:
Are they a problem, and what can be done about them? 

As I’ve said before, wine gets you drunk. It’s because wine is an alcoholic drink. This sounds like a rather facile statement, but it’s something we can forget in our high-end, anoraky discussions about first growths, super seconds and Grand Cru Burgundies. It’s part of the point of wine, isn’t it? That’s why it’s the social drug of choice in western countries.

Now, after being relatively ignored by the wine trade, the subject of wine’s alcoholic content is currently a hot topic. This is because there’s increasing concern about the trend of rising alcoholic levels. Table wines used to hover around the 12% mark: now it’s rare to find them below 13%, and wines with 14 or 14.5% alcohol are commonly encountered. And it’s not all that unusual to see wines tipping the scales at 15%. This feature takes a broad-perspective look at this topic, asking why it is that these rising alcohol levels are a concern, and then looking at what can be done about them.

The basics 
Alcohol is produced by the fermentation of sugars by yeast, and so it follows that the higher the sugar level in the grapes, the higher the final alcohol level in the wine when it is fermented to dryness. Sugar accumulates in grapes during the ripening process, being produced by the process of photosynthesis in the leaves and stems of the grapevine.

The rate of photosynthesis is determined by the intensity and duration of light, plus the ambient temperature, in a rather complex relationship. In brief, photosynthesis is maximized in warm, sunny conditions where there is lots of light and the elevated temperatures cause chemical reactions to occur at a faster rate, but if it is too hot, photosynthesis stops because the vine closes its stomata (gas exchange pores) to reduce water loss. Thus we can have a situation where in hot regions, development lags behind warm regions because photosynthesis will have ceased during the warmest hours of the day.

The ripening process
Conceptually, it helps to distinguish two distinct ripening processes in grapes. I should add that this is perhaps a slightly simplistic dichotomy that is disputed by some, but I think it serves a useful conceptual purpose.

  1. Sugar ripeness: as the grapes mature, the sugar levels rise and the acid levels decrease.
  2. Phenolic or physiological ripeness: changes in tannins, reduction in methoxypyrazine levels, leading to ‘flavour ripeness’.

In cool climates, the physiological ripeness precedes sugar ripeness. Indeed, throughout much of Europe, the only measurement required as harvest time comes round is the level of sugar in the grapes. Once this reaches a certain level, you can assume that the grapes are ripe. And in many regions, the addition of sugar to the must in a process known as chaptalization is carried out because full sugar ripeness hasn’t been achieved. Acid levels are commonly quite high at harvest in cool climates.

In ideal climates the two ripenesses intersect: physiological maturity is reached at a sensible sugar level, where the acidity is also at the appropriate level.

In warm climates, physiological ripeness frequently trails sugar ripeness. Thus winemakers who wait for physiological ripeness often have to contend with high sugar and thus high alcohol levels, and need to acidify, too. Generally speaking, a lack of physiological ripeness is more detrimental to wine quality than a lack of sugar ripeness: it’s much easier to correct for a lack of sugar ripeness than it is to correct for a lack of physiological ripeness. This is because many of the compounds involved in physiological ripeness are antifeedants: the green-tasting methoxypyrazines and bitter tannins are presumably intended to make immature grapes unpalatable to birds. They decrease as the grape matures, to the point where the vine is ready to let the birds to take the grapes to propagate the seeds.

Sugar levels can also increase by desiccation, where the grapes lose water, concentrating both sugar and acidity. This is dubbed ‘saggy grape syndrome’, because of the way that the skins begin to pucker.

In recent years there has been more of an emphasis on achieving flavour/physiological/sugar ripeness through later picking. This is where we encounter the phenomenon known as ‘hang time’. Where harvest occurs in the autumn, picking decisions are often influenced by weather concerns: the grapes are brought in before the autumn rains. In warmer climates with settled harvest weather, the grapes can be left as long as needed: the temptation is to pick late, allowing what is known as ‘hang time’. It is controversial, because changes occur to the tannic structure and the fruit profile, which, in its most extreme incarnation results in wines that show ‘dead fruit’.

Why have alcohol levels increased in recent years?
There are a number of explanations for elevated alcohol levels in wine, although we don’t have enough data to separate them.

1. Global warming: data show that over the last 50 years average temperatures in most wine regions have risen noticeably. Warmer growing seasons usually result in riper grapes with higher sugar levels.

2. Improved viticulture has led to grapes being picked in a riper state than they were before.

3. Stylistic changes: winemakers have opted for later picking to produce wines with sweeter fruit profiles, made in an ‘international’ style.

One explanation that has been touted is that modern strains of yeast are more efficient at converting sugar into wine, but this proposed improved yeast efficiency is probably not a reason for higher alcohol, simply because there is no evidence that the yeasts use today are any more efficient than those that used to be used. The conversion factor has remained pretty stable.

Why are increased alcohol levels a cause for concern?
The least concerning aspect of rising alcohol levels is the increase in alcoholic content itself: after all, it’s easy enough just to drink a little less of the wine.

The main concern is the effect of high alcohol on the sensory properties of the wine. Relatively small changes in alcohol content can have quite a strong influence on how the other components of the wine are perceived. I find I don’t really enjoy wines with higher alcohol as much because of the effects of the alcohol on the nose of the wine, and the bitter/sweet/salty character the alcohol lends to the palate. Yes, I do enjoy Port, which has 20% alcohol, but there, allied to higher alcohol levels, we also have sweetness.

The other significant concern surrounds issues of ‘style’ or ‘taste’. Decisions about when to pick have quite an influence on how the wine will come out. In recent years there has been critical influence, largely from the USA, pushing red wines (in particular) towards a homogenized ‘international’ style. I realize this statement could form the basis of a feature all on its own, but for now, I’m tempted just to say that red wines showing higher levels of ripe fruit, accompanied by softer tannins and plenty of new oak influence often get very high scores from the leading critics, whose ratings then influence sales, most notably in the USA where critical scores have a strong effect on sales. When grapes are picked late to achieve this style, and lots of new oak is employed in the elevage, the sense of place (or terroir) of a wine is often masked. Wines ending up tasting similar no matter where they have come from. [Yes, this is a controversial assertion that needs backing up with examples – but this will have to be done some other time, perhaps in another feature.]

What can be done about it?
There are three approaches to deal with higher must sugar levels, leading potentially to higher alcohol in the final wine.

  • In the winery: alcohol reduction
  • In the vineyard: viticultural interventions and decision-making
  • For the future: yeast development

Alcohol reduction
The first approach is to remove alcohol from the wine after fermentation. Three methods are currently used of which only two are legal: reverse osmosis and the spinning cone. The third is the addition of water to the must, which isn’t allowed but is practiced quite widely in warmer regions.

Reverse osmosis is a filtration device that employs a technique known as cross-flow filtration. Rather than direct the flow of liquid at a filter, which results in the filter gradually becoming blocked with the filtrate, the flow of liquid is in parallel with the filter membrane, and thus the flow itself keeps the membrane free of blockage. So a counter current filter will look like a long tube, with the walls being made out of the filter membrane. As the liquid passes through the tube, it is filtered, but a much larger membrane surface is clearly needed with this technique.

Reverse osmosis takes water, alcohol and other small molecules out of the wine, the alcohol is taken out by distillation, and then the water is recombined back with the wine to make a low alcohol wine which can then be used for blending with untreated wine to produce a final wine with precisely determined alcoholic content. Other variations on this theme exist. Many wineries have their own reverse osmosis machine; others get this done on a contract basis.

The spinning cone is a bit more complicated. It separates off the volatile components from the wine which are then fractionated. The important bits are kept and the alcohol is selectively removed. Because this machine is big, the winery has to send the wine to a contract facility for treatment. The end result – a wine with a reduced alcoholic content – is the same.

There’s a concept worth mentioning here: that of the sweetspot. The notion is that if you line up glasses of the same alcohol-adjusted wine at a range of alcohol concentrations, say from 12 to 15% at 0.1% increments, some will work much better than others. The same wine may have a sweetspot at 12.8, another at 13.2 and another at 14.1, as if you were tuning into radiostations. For more on this, see an interview I did with Clark Smith (pictured right), whose company, Vinovation, specializes in fine-tuning the alcohol levels of wine.

There seem to be gains and losses associated with the use of such technologies, and the balance between the two seems to depend on who you talk to. On the plus side, many wines show much better with reduced alcohol levels. On the negative side, these sorts of treatments are quite physical, and may beat the wine up a bit. It’s hard to debate the subject in a relative absence of good, independent data.

Vineyard intervention
It is hard, but not impossible, to make changes in the vineyard to try to get grapes fully physiologically ripe without sky high sugar levels. Of course, the first question that needs to be asked is whether just picking earlier might work. Growers don’t want grapes that have green, unripe flavours, but it could be argued that some are currently picking later than they need to. Again, this gets back to the style issue that we have already discussed.

Any vineyard intervention that achieves more homogeneous ripening is going to help. If the various patches of a vineyard are ripening at different rates, then picking may be occurring later than is ideal for some bits, as growers wait for late-ripening bits to ripen while other bits are over-ripe with desiccated, raisined berries in some bunches that just add sugar and little else to the must. Green harvesting the latest bunches to go through veraison is a useful intervention, as is identifying and understanding the natural variation that occurs within the vineyard. 

If irrigation is present, this can be used as a tool towards the end of ripening to help control sugar levels in grapes. Sometimes adding a bit of water before harvest can be a good thing, because it may buy a few more days for flavour ripeness to complete while offsetting the natural rise in sugar concentration that would otherwise occur during this period.

Organic/biodynamic viticulture may help, although this is a large, complex subject that can’t be done justice in this context. I’ve heard quite a few growers report that since they shifted to an organic regime that had at its core the use of compost to build up organic material in the soil, they’ve found it easier to get ripeness at sensible sugar levels. It may also be that manual tilling of the soil encourages the vine roots to sink deeper, from where they are able to extract a slow but steady supply of water during the period preceding ripening. 

The canopy is likely to be important here. Leaves are the factories that, through photosynthesis, produce sugar. Growers need a canopy that is appropriate for the crop they are planning to take. Sometimes a 6 foot wall of wines might have just too much photosynthetic power for a small crop.

Factors such as row spacing, vine density, pruning decisions, canopy height, fruit shading, and water availability will combine together to influence the vine’s physiology when it comes to ripening the crop. There are a lot of variables that need to be understood and manipulated where possible.

Yeast development
The final tool that could potentially be used in the war against high alcohol is the organism responsible for making alcohol in the first place, the alcogenous yeast Saccharomyces cerevisiae. Yeasts produce alcohol from metabolizing sugar. If by selective breeding or genetic modification we can get yeasts to use a different metabolic pathway, one that, for example metabolizes sugar to glycerol, then the yield of alcohol per gram of sugar will be less. There are currently a number of projects looking at this possibility, and it may well be that in five years time yeasts will be on the market with a lower conversion factor. But this is currently some way from being a practical option.

In conclusion, along with much of the trade, I consider the rising alcohol levels in wine to be a bit of a problem, and one that needs addressing. It’s perhaps unfortunate that many of the potential solutions are so manipulative in nature, at a time when the naturalness of wine is an issue coming under increasing public scrutiny. I have a general guiding principle when it comes to winegrowing: if you are going to intervene, the earlier you intervene in the winegrowing process the better. Thus I feel that of all the solutions to high alcohol offered here in this brief review, the most promising is the set of vineyard interventions that may well help in producing fully ripe grapes at lower sugar levels.   

Article published December 2007

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