How is the sweetness of wine measured?

Like so many elements in the fascinating world of wine, the concept of sweetness is often open to debate. For some connoisseurs, a wine may only be considered sweet if it falls among those categories boasting the highest levels of residual sugar, such as Tokaji and Passito wines. For others, wine is a decidedly ‘dry’ invention and talk of sweetness has no business here at all. As always, personal taste reigns supreme, so let’s stick to the facts.


What makes a wine taste sweet?

Winemaking is an exact science, with every single component that goes into a wine – from yeast and preservatives to the grape variety itself – ultimately affecting the eventual flavour profile. And even then each wine will be experienced differently by different people, based on their unique sense of smell and saliva makeup. However, while levels of tannin, alcohol and acidity play a significant role in a wine’s perceived sweetness, the biggest factor is residual sugar. It probably won’t surprise you to learn that the more residual sugar there is in a wine, the sweeter it will be.


What is residual sugar?

Residual sugar (often abbreviated to RS) is the naturally-occurring grape sugars left in a wine after the alcoholic fermentation process is completed. Dry wines will also often contain some level of RS – usually to help balance high acidity. It’s measured in grams per litre, with 10 grams per litre of residual sugar giving a 1% sweetness level. An interesting titbit: the average wine drinker generally can’t detect sweetness levels below 1.5%, whereas trained tasters can estimate sweetness within about 0.2%!


How sweet is my favourite style of wine?

There are generally-accepted RS parameters for each category of sweetness (or dryness, depending on how you look at it), for both red and white wines. Again though, the exact numbers are often subject to debate depending on the region, grape and/or winemaker.



Dry – 0-2%
Muscadet, Sauvignon Blanc, Pinot Gris, Chardonnay, Chenin Blanc, Viognier.

Off-dry – 3-6%
Gewurztraminer, Riesling.

Sweet – 6%+
Moscato, white Port, ice wine.



Dry – 0-2%
Sangiovese, Tempranillo, Cabernet Sauvignon, Pinot Noir, Syrah, Merlot, Malbec, Zinfandel.

Medium sweet – 6-9%
Lambrusco Dolce.

Sweet – 10%+
Port, Tawny Port.


How are sweet wines made?

Just as individual grape varieties better lend themselves to certain growing conditions, each will also have optimal sweetness parameters, which can be controlled during the winemaking process – and it all comes down to yeast.

During alcoholic fermentation, yeast feeds on the sugar found in grape juice and converts it to ethyl alcohol, or ethanol, and carbon dioxide. The amount of sugar fermented determines the wine’s alcohol level and the amount of residual sugar left in the wine. To produce off-dry or sweet wines, the winemaker will intentionally halt the fermentation process prematurely, usually by lowering the temperature – chilling the vat paralyses the yeast, preventing it from completing its ‘job’, thereby leaving residual sugar.

Dessert wines, meanwhile, are typically made from dried grapes which have a much higher sugar-to-juice concentration. Here, the yeast will gorge on the sugar and die off as the alcohol rises, still leaving behind extra sugar. Sweet Port is made in a third way, with fermentation paused halfway through production and a high-alcohol spirit added to kill the yeast, once again leaving behind natural grape sugar.


Is sugar ever manually added to wine?

In some cases, yes. Many sparkling wines and German Rieslings have a high acidity – and subsequently a very sharp taste – that can be balanced out with natural, unfermented grape juice. And during Champagne making, producers may adopt a step called ‘liquer d’expedition’, where they add a small amount of grape must or sugar before corking the bottle.

Some producers in cooler climate regions will also practice ‘chaptalization’. This is where sugar is added before or during fermentation and is used to increase the total alcohol level when under-ripe grapes have been used. However, this process isn’t meant to increase the sweetness of a wine, and is generally subject to criticism by those that see it as unnecessary interference.


How can I find out how much RS is in my wine?

The short answer is, you can’t – not easily, anyway. Since wine isn’t required to include nutrition information on its labelling, there’s no reason for producers to add details about sugar content. That being said, with the exception of a few occasional instances (as mentioned above), any sugar found in a wine – dry, sweet or otherwise – will usually be naturally occurring, and not at all like the sugar often mentioned in additive scare stories found in the news.


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