Natural sweet wines, between shriveling, noble rot and ice

Not to be confused with VDN, the French term for fortified wines, these wines are called sweet wines in the UK. Traditionally they are sweet wines taken at the end of a meal and especially for the dessert as opposed to fortified wines such as Port and Sherry that are mostly taken before or after a meal.

Natural sweet wine is a black or white wine for which the residual sugar content is high and for which the alcoholic fermentation has stopped without any addition of alcohol as opposed to a fortified wine.

As a consequence, it is a conjunction of both the vineyard work and a specific winemaking technique which give this sweet, even luscious character.

Whatever is the winemaking technique used the starting point is in the vineyard, as for all wines you would say. Yes indeed, but here specific conditions are sought by the winemaker to produce these sweet wines. These conditions are not found everywhere in France or elsewhere in the World. What we need here is a highly concentrated grape, both in sugar and aromas. Concentrated enough to make yeasts struggle to ferment leading the fermentation to stop by itself in some cases. Resulting wines will be sweet or luscious with a full body and pronounced dried and candied fruits character with a long finish. Good level of acidity will be part of these wines.

There are 4 techniques that allow to concentrate sugar, aromas and acidity to produce natural sweet wines. They are adapted to the vineyard location as well as to the grape variety used. These are: drying of the grape on the vine, drying of the grape off the vine, the noble rot (aka Botrytis) and the freezing of the grape on the vine (aka ice wine).

The only common feature to all of these techniques is the natural high acidity of the different grape varieties used that promote the balance sugar/ acidity needed for this kind of sweet wines.  

Drying of the grape on the vine

During the vine cycle the grape goes through different stages where the organoleptic properties set up. Acidity is really high at the beginning and then become smoother, the low sugar level at the beginning starts to increase and then aromatic precursors evolve. By the time of harvest the grape is in balance between all these parameters.

For the VND the winemaker is looking for an another step. He/she will leave the grape on the vine during the late season so that the grape will start to shrivel thanks to the evapotranspiration process (water inside the berry evaporate). For this to happen specific climatic conditions are required. A dry and sunny autumn is more than welcome to prevent any grey rot development which would compromise the process. This shriveling implies a loss of water inside the berry leading to a concentration of sugar within the grape. Moreover, acidity levels increase because it is not diluted anymore by the water from the grape and finally aromas concentrate and evolve to the dry and candied side. This phenomenon is called « passerillage » (shriveling).

Regarding the winemaking processes the juice which is lower in quantity (compared to a standard wine) is pressed and starts the alcoholic fermentation with some difficulties because of the high sugar content. Fermentations are long and stop by themselves but it is possible to stop it by cooling down the must and/or by adding SO2 to stabilize the wine. As a matter of fact, a sweet wine is more susceptible to ferment again compared to a dry wine.

Resulting wines are labelled « late harvest » (« vendanges tardives ») in Alsace with the use of Riesling for instance or are labelled « Spätlese » in Germany and Austria.

Another way of doing it is to cut the grape that is over-matured and to leave it in the vineyard, by putting it in a net or by hanging it to a wire. The same process than previously explained takes place: sugar, aromas and acidity concentration but faster because the grape is not fed anymore by the vine. This avoid grey rot development and the resulting aromas are still on the candied fruits side but lesser. Winemaking techniques follow the same process than previously explained.

This technique is used in the Jurançon AOC using the Petit Manseng grape variety.

Drying of the grape off the vine

Oppositely to the drying on the vine this technique requires a healthy grape, mature enough to still have high acidity. The grape is hand-harvested then put into wooden racks (or hung up to wires, or put onto a concrete table) in a dry and aerated place in cool regions such as North Italy. In warmer regions such as Spain, Corsica and South of Italy it will be put under the sun.

The winemaker leaves the grape to dry for a period of 2 to 4 months depending the wine region. During this time the grape will dry, shrivel, sugar and aromas concentrate and acidity levels increase. Winemaking process follows the same path as previously explained. Resulting wines show complex and concentrated aromas of early dried fruits, some fresh fruits notes with a vivid acidity and noticeable residual sugar. In Italy this process is called « appassimento ». It is used to produce the famous wines of Recioto della Valpolicella using Corvina red grape, Vin Santo in Tuscany using a blend of Trebbiano Toscano and Malvasia white grapes. In France it is used to produce « Vin de Paille » in Jura using Savagnin grape mainly.

Noble rot

This concentration technique is very specific to some wine regions because of the need of particular weather conditions.

It is a fungus, called botrytis cinerea, which is responsible of this concentration. More precisely it is the consequence of the attack of this fungus on the grape that leads to this concentration.

The starting point is a healthy mature grape evolving in a humid place with fog or mist in the morning and sunny and dry afternoons. Such conditions are found in the Sauternes region near Bordeaux for example but also in the famous Tokaj region in Hungary.

Damp mornings are perfect for the botrytis development that feed and live on the grape’s skin. By doing this it creates holes within the berry which, when dried under the afternoon sun, loses its water. It is an ideal condition to promote sugar, aromas and acidity concentration then.

Great care needs to be taken because if these specific conditions are not found the botrytis, also called noble rot, will become grey rot and destroy the grape.

This process is uncertain and heterogeneous in the vineyard but also within a same grape consequently a long and hard sorting work needs to be done. Therefore, this style of wine is not produced every year and a skilled workforce is mandatory. All of this contribute to the price and rarity of these wines.

Fermentations are again longer because of the high sugar content in the grape. Wine production is also lower because less juice is produced after the press.

The more the affected grape is left on the vine before to be harvested the more it is concentrated. Typical aromas from botrytis are honey, orange zest, candied apricot and a hint of ginger in addition to the grape’s aromas. In this way, a wine made thanks to botrytised grapes can show a uniqueness with different levels of concentration depending on the style and the wine region where it is produced.

In France, in the Bordelais, the Loire or even in Alsace these wines are luscious, deep and concentrated in sugar and aromas. They are made with 100% of botrytised grapes. However, concentration within the grape is not pushed to the limit so they still have some freshness.

In Hungary berries are left for a longer time on the vine and so have a deeper concentration. We can find to the extreme side of concentration the Ezsencia which is a really syrupy wine, highly sweet, luscious and very rare.  Most commonly we can find the Tokaj Azsú wines made with different proportion of botrytised berries added to a dry wine. These wines are similar in style to the French wines but with a botrytis concentration more pronounced.

Wines from Sauternes and Barsac, between others, in the Bordelais using Semillon mainly, Coteaux du Layon in the Loire Valley using Chenin Blanc, Trockenbeerenauslese in Germany with Riesling or even Tokaji from Hungary using Furmint grape are all made thanks to this process.  

Freezing the grape on the vine

Last but not least here is a natural technique to concentrate sugar, aromas and acidity: the frost. Indeed, frost allows to solidify the water inside the berry. A healthy grape is left on the vine through winter. When animals have not eaten it and when temperatures drop below -8°C(!) the grape is hand-harvested. Then the winemaking process is long because little juice is collected after the frozen grape is pressed from one side and from the other side the fermentation takes a lot of time. The winemaker ends up with a true nectar, very luscious, concentrated but really fresh in the meantime providing dried and candied fruits notes. Wines made this way are called Icewine.

Of course, not all the grape varieties can handle such climatic conditions. Riesling and Vidal are the best known and the most resistant to this extreme cold speaking about white grapes. Cabernet Franc can also produce icewine but less frequently.

With the global warming it is more and more difficult to produce this kind of wines. Canada is the main producer of icewine in the world but Germany and Austria produce it too.

There is a technologic alternative to this which consists in harvesting the grapes in autumn and then to freeze it artificially. This is called the « cryoextraction ». It is really energy consuming so less and less people use it nowadays. It allows to save time and to prevent to lose the crop because of winters that are not cold enough to produce naturally icewine.

What about wine and food pairing then? Remember at the beginning I wrote that in the UK they talk about VND as dessert wines. All is a matter of taste and it is quite subjective but you need to keep in mind that the wine needs to be as sweet or sweeter than the food you want to pair with but not only! These wines are round, they have a full body because of the high sugar content, usually acidity is high enough to make you forget the +100g/L of residual sugar. They are also quite complex in term of aromatic.

A classic match is to pair it with foie gras or for the aperitif… I admit that this works but it is a shame to saturate your mouth with such sugar and fat at the start of a meal… Why not pairing it with an apricot pie? Or a blue cheese? Or a dark chocolate? Or even… by itself!

And you, what kind of natural sweet wine would you like to taste?

Gauthier Bernardo DipWSET, FWS