Natural (unfortified) wines usually contain alcohol concentrations of between 11 and 16% alcohol by volume. In South Africa, which is considered a warm viticultural climate, alcohol levels usually range between 13 and 16%.
Factors that influence final alcohol concentrations in wines:
- Climate of the viticultural area
- Specific viticultural practices
- Grape cultivar
- Disease state of the vineyard
- Harvesting date i.e., initial grape sugar before fermentation
- Residual grape sugar after fermentation
- Fermentation temperature
- Fermentation vessel
- Winemaking legislation – permissible products and processes
- Stylistic preferences of consumers
How alcohol is formed – the role of yeast
Alcohol is formed by yeast during fermentation. Yeast metabolises grape sugars (glucose and fructose) to form ethanol (alcohol) and carbon dioxide. If a 100% conversion occurs, 180 g of the sugars will form 92 g ethanol and 88 g carbon dioxide. In practice it does not happen, seeing that part of the sugars is used for yeast cell material and other by-products.
In the cellar the sugar levels of grape juice and fermenting musts are measured in degrees Balling using a hydrometer, since it is a quick and easy method for winemakers to monitor their fermentations. There is a correlation between degrees Balling and actual g/L of sugar, although not very accurate at very low and very high degrees Balling.
The sugar to alcohol conversion factor can be expressed in one of two ways. Firstly, the sugar mass, which is required to form 1% by volume ethanol, namely 16.83 g/L sugar or secondly the percentage alcohol per unit of the density index, namely 0.59% ethanol per degree Balling. Research has shown that the conversion factor of yeast strains varies from 16.5 to 17.2 grams sugar per 1% alcohol by volume, which correlates with 0.581 to 0.606% ethanol per degree Balling. The European Union has agreed on a conversion factor of 16.83 g sugar per 1% alcohol per volume, which correlates with 0.594% ethanol per degree Balling.
It was found, through various research projects around the world, that Saccharomyces species wine yeasts are very similar in their conversion from sugar to alcohol. Wine yeast selection is therefore not the typical route to produce substantially lower alcohol wines, likely only about 1% lower if certain non-Saccharomyces yeasts are part of the fermentation.
Various research projects all around the world, over a time span of more than 20 years, have also attempted to manipulate wine yeasts to produce less alcohol from a given amount of sugar. This was not possible without substantially damaging wine quality. Some success was achieved by using genetic modification of the yeast’s DNA, but this is not permitted in the production of commercial wine yeasts or winemaking, nor is it acceptable by wine consumers.
TAKE OUT: CURRENTLY, WINE YEAST SELECTION IS NOT TYPICALLY USED TO REDUCE ALCOHOL LEVELS IN WINE AS IT CANNOT REDUCE THE LEVELS MUCH (0.5 – 1%).
Grape juice initial sugar levels
One can argue that the most obvious way to get lower alcohol concentrations in wines would be to simply pick the grapes earlier. This is also not that simple. Grapes are picked when they are ripe for the same reasons why we eat only ripe fruits. It is the time when they taste the best. Unripe grapes don’t taste nice and do not produce nice tasting wine. Wines need to taste nice for one to be able to sell it to consumers and generate an income.
Grapes are usually picked between 20 – 26° Balling. Generally, grapes with sugar levels lower than 20° Balling are unripe and grapes with sugar levels over 26° Balling are either overripe or dehydrated, meaning they did not ripen to that sugar level, they lost water and the sugar concentrated to that level – the way raisins are formed.
In South Africa, because of our generally warmer climate than most viticultural areas in Europe, our grapes are picked at slightly higher sugar levels than grapes in Europe. This is a major generalisation though and in many warmer areas in Europe, grapes are picked at similar sugar levels than in South Africa. The reason why warmer areas pick grapes with higher sugars is because we don’t only pick grapes on sugar ripeness but also on phenolic ripeness. Grapes can have a high enough sugar for harvesting but can still contain a “tartness” due to the phenolic substances in the grapes that can have a “drying out” effect in the mouth when people drink wines containing unripe phenolic substances. Consumers don’t like this taste in wine. In warm areas sugar ripeness is much faster than phenolic ripeness and by waiting for phenolic ripeness, sugars tend to be higher than in the case of cool climate grapes. There the two ripening processes are more synchronised and grapes can be picked at lower sugar levels.
A factor that should also be kept in mind is climate change. Research has shown how the initial sugar levels of grapes in France and the resulting alcohol levels of wines have increased substantially over the last 10 years. Whereas French wine traditionally easily contained alcohol levels as low as 12% for red wines, 14% is not uncommon nowadays. The same trends have been observed in other wine producing areas of the world. Climate change has more significant consequences in warm viticultural areas where it can lead to grapes being picked at sugar levels resulting in alcohols above 14% and even 15%.
TAKE OUT: HARVESTING UNRIPE GRAPES AT LOWER SUGARS TO ACHIEVE LOWER ALCOHOL IS NOT GOOD FOR WINEMAKING. GRAPES HAVE TO BE PICKED AT THE RIGHT RIPENESS FOR SUGAR LEVELS, FLAVOURS, AROMAS AND STRUCTURE OF WINE TO BE CORRECT, WHILE ACHIEVING THE OPTIMAL WINE ALCOHOL LEVELS.
Consumers are very particular in what styles of wine they prefer. Winemakers around the world don’t have the luxury of just producing wines they want to and hope someone will buy it. They must produce styles people are willing to buy. In the case of white wine people prefer fruity smelling and tasting white wines. To produce such wines, viticulturists and winemakers must wait for grapes to contain enough fruity compounds before they can harvest the grapes. Most flavour active compounds in grapes increase with ripening. The later you pick, the more flavour in the grapes. So, winemakers must strike a balance between where they will have enough fruit flavours in the grapes and resulting wines and the alcohol levels that will still be acceptable by consumers. The fruity aromas and flavours in wines are more important for consumers than the alcohol levels. Alcohol levels of 13 and 14% in white wines are in general acceptable to consumers.
In the case of red wines, consumers like different styles. Mostly they prefer fruity red wines that are full on colour and have a firm but smooth mouthfeel. The same principle applies in terms of flavour active compounds increasing with ripening as they are mostly the same compounds found in red and white grapes, albeit in different concentrations and combinations. In the case of red grapes colour and tannins (responsible for mouthfeel) also increase with ripening. Since red grapes are fermented on skins to extract colour and tannin it is very important that these tannins must be smooth tannins and not unripe “green” tannins that can impart a tartness to the wines.
Due to these consumer preferences winemakers can only make wines from full ripe grapes, which in South Africa result in alcohol levels between 13 – 15%. Deliberative picking grapes earlier will result in less fruity wines and less sales and revenue for wineries.
TAKE OUT: IF YOU CHANGE THE STANDARD WINE ALCOHOL LEVELS OUTSIDE 13-15%, IT CHANGES THE AROMA AND MOUTHFEEL OF WINE TO SUCH AN EXTENT THAT CONSUMERS MAY NOT LIKE IT ANYMORE AND THE PRODUCT IS OUT OF BALANCE.
Strategies to manage alcohol levels in wines
Wineries are very conscious of the dangers of high alcohol beverages and they constantly implement strategies to deliver wines with the lowest possible alcohol concentrations considered acceptable for white and red wines. The following strategies are in place in the South African wine industry.
- Viticultural practices that can to some extent manage the ripening process of grapes.
- Harvesting at the lowest possible sugar level, keeping the grapes’ flavour profile and phenolic ripeness in mind, that can deliver wines consumers would like to drink.
- In the case of red wines that tend to have higher alcohol levels, winemakers do regular pump-overs that can lead to some evaporation of alcohol. Red wines are also fermented at warmer temperatures and often in open top fermenters that can also improve evaporation of alcohol. These techniques can lead to a 0.5 – 1% alcohol loss due to evaporation.
- Wines that contain alcohol levels over 15% are subjected to alcohol removal strategies to lower the alcohol levels to under 15%. Reverse osmosis has been applied for lowering alcohol by 1-2% in the past, but it changes the wine’s composition and flavours too much and can very easily do more damage to wine.
Spinning Cone technology is the most common way to lower alcohol in wines. Final wine alcohol can be lowered substantially with this technique and wines can even be totally dealcoholised. However, when lowering alcohol substantially, say more than 2%, the wine will taste substantially different to the original wine. The same flavours and aromas can taste completely different at 8% alcohol than at 14% alcohol, and even imply the wine becomes disliked. One cannot just change alcohol levels. Also, alcohol affects the colour and stability of the wines, which will also need to be rectified. Winemakers therefore use this technique very conservatively to avoid reducing wine quality.
NOTE: Spinning Cone technology currently has limited capacity in South Africa and is a service that is provided. Wineries do not have this as general/standard equipment in their cellars.
- Blending wine with grape juice is also considered if the final product outcome needs to be sweeter and contain higher residual sugar levels.
Key take home message
In South Africa we naturally have alcohol levels in our wines between 13 – 15% because of our warm climate and because of the styles consumers prefer. We make every effort possible and legal to maintain alcohol levels in this bracket or even to lower it. We constantly do research and follow international research to see if there is a way to produce wines consumers would like to drink but at lower alcohol levels. However, at this stage we are 100% on par with the alcohol levels in wines from other new world and mostly warm wine producing countries i.e., the USA, Australia, Argentina and Chile.
The author would like to thank Dr. Adriaan Oelofse (Winetech) and Yvette van der Merwe (SAWIS) for their contributions to the article.
- Different techniques for reducing alcohol levels in wine – A review: https://www.bio-conferences.org/articles/bioconf/pdf/2014/02/bioconf_oiv2014_02012.pdf
- Making sense of warm and cool climates: https://www.wineland.co.za/making-sense-of-warm-and-cool-climates/
- Predicting alcohol levels: https://www.awri.com.au/wp-content/uploads/2018/04/s1809.pdf
- Rising alcohol levels – How winemakers are adjusting: https://daily.sevenfifty.com/taking-control-of-alcohol-levels-in-wine/
- The conversion of sugar to alcohol: https://www.wineland.co.za/the-conversion-of-sugar-to-alcohol/