Sugar, yeast, ice, mould - what makes French sweet wine…sweet?

Winemaker Jonathan Hesford explains how sweet wines are made

A mould ,Botrytis, can cause grapes to concentrate their sugars. The most famous botrytis wine is Sauternes from Bordeaux

One particular characteristic which often separates wines, and also the opinions of consumers, is sweetness.

Sweetness is perhaps the only taste that is actually categorised and named on the label.

Many French wines bear a word that tells the consumer how sweet the wine is likely to be.

These include Sec, Brut, Moelleux, and Doux.

However, not all wines bear those words and consumers are expected to know what they are buying based on the name of the Appellation (AOP), such as Sauternes.

Then there are confusing AOPs which can be dry or sweet. Vouvray springs to mind.

Sweetness is almost always due to the presence of sugar, usually from unfermented grape juice.

Yeast is the key

There are three main ways of making wines with residual sugar. All of them rely on stopping the yeast from consuming all the sugar in the juice.

Yeast can only tolerate an alcohol level of between 15 to 17%, depending on the individual strain.

Therefore if the juice has a potential alcohol level over 15%, it is likely that the yeast will die before it has fermented all the sugar in the juice.

Leave the grapes to over-ripen

The simplest way to make sweet wine is by picking extremely sweet grapes.

This can be achieved by leaving the grapes to over-ripen and shrivel on the vine.

It is only possible in regions with a warm, dry autumn because otherwise the grapes will either rot or stop ripening as the leaves fall off the vine.

Such wines are termed Vendanges Tardives, meaning late-harvest.

In France they are mainly found in Alsace and the Western Pyrenees such as Jurançon and Gaillac.

They are also common in Germany and Austria where they are labelled Spätlese.

The style works best with aromatic grape varieties such as Riesling, Gewürztraminer, Muscat and Pinot gris. The wines have a medium level of sweetness.

Mouldy grapes make sweet wine

Having the grapes rot on the vine is not always a bad thing.

Botrytis, a type of mould, can, under the right conditions, cause the grapes to concentrate their sugars even further without developing any sour, acetic acid (which is caused by bacteria).

When Botrytis does this, it is called “Noble Rot”.

It requires very specific climatic conditions of rain followed by a dry period.

The grapes do not all develop the noble rot at the same time so the bunches need to be selected and picked as and when they are ready, unlike grapes for dry wines which are picked all at the same time.

Therefore making Noble Rot wines is more difficult and costly than making dry or late-harvest wines.

These wines are much sweeter and have the additional, honeyed flavours created by the rot.

In France, the most famous examples are Sauternes from Bordeaux, Monbazillac from around Bergerac and Coteaux du Layon from the Loire.

These “Botrytised” wines are also made in Alsace where they are called Sélection de grains nobles.

In Germany and Austria they are called Auslese or Beerenauslese. However, the first wines made from Noble Rot originate from Tokaj in Hungary.

Grapes freeze on the vine

In regions where winter comes on quickly, the late-harvest grapes may freeze on the vine.

They can then be picked and pressed while still frozen to collect super-concentrated juice which can then be fermented into Eiswein, the sweetest of all wines.

Fortified wines

The other traditional way of stopping yeast from fermenting is to raise the alcohol level by adding distilled grape spirit.

The method, known as fortification, rapidly increases the alcohol content of a fermenting wine over the 16% resulting in a wine high in both sugar and alcohol.

This method is said to have originated in the Roussillon in the 17th century, resulting in the Vin Doux Naturel wines of Banyuls, Rivesaltes and Maury.

The technique was carried down the coast of Spain, where it was used to make Moscatel until it reached Jerez where the producers developed a unique style of fortified wines which we Anglophones call Sherry.

British and Irish wine merchants introduced fortification to the winemakers of Porto, creating Port, and to the island of Madeira.

Removing yeast produces sweetness

Grapes harvested at lower ripeness levels can also have their fermentation stopped to leave enough noticeable sugar for the wines to be termed medium dry or semi-sweet.

It also has the effect of reducing the alcohol level. This is commonly achieved by filtering the wine during fermentation to remove the yeast.

The method is used to make Moscato in Italy and certain wines from Bordeaux and Gaillac in France where the term “Moelleux” is usually found on the label.

Adding sugar or dosage

Finally there are wines which are sweetened after fermentation to achieve a flavour profile desired by the producer. The classic example of such “dosage” is in sparkling wines, including Champagne.

The labelling is confusing because “Dry” Champagne has between 17-32g per litre of added sugar and Brut can have up to 12g/l. The only truly dry Champagne is labelled “Brut Nature”.

In the New World, many popular brands of supposedly dry wine are sweetened by stopping the fermentation early or by adding sugar or concentrated grape juice after fermentation to make them more acceptable to consumers.

It may come as a surprise to many that “dry” wines like Oyster Bay and Blossom Hill have between 5 and 12g of sugar per litre and others such as Barefoot are closer to 20g/l making them essentially a medium-sweet red wine.

Sweet trick

It’s worth noting that consumers often say a wine tastes sweet when it has no residual sugar.

This is usually because of glycerol, naturally produced by the yeast during fermentation, which gives the semblance of sweetness while not actually being a sugar.

Ethanol, the main alcohol in wine, can also seem to add sweetness.

Lastly, a “sweet” smell can confuse people.

I’ve had many people say that my “Muscat Sec” tastes sweet, even though the analysis shows it has no sugar, because they associate the smell of Muscat with sweet wines.

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