How is Sweet Wine Made?

Method 1: Adding Sweetness Before Fermentation

Some of the best sweet wines are made by concentrating the sugar level in the grapes at the beginning of the winemaking process. This is so that some grape sugar can survive the entire fermentation process without being converted into alcohol and carbon dioxide. The idea is to have grapes that are so intensely sugary, that the yeast dies off before it has a chance to convert all of the sugar from the juice (Yeast naturally dies at 15% ABV).

One way of concentrating the sugars in the grapes is to use fruit that has had water evaporated out of it. Grapes that have been left on the vine for a long time can start to dry out, so picking them late harvest can be ideal for making sweet wine. Alternatively, winemakers sometimes lay freshly picked, healthy grapes out in well-ventilated, dry conditions to encourage evaporation and dry the grapes out before crushing them for fermentation. The famously intensely sweet PX Sherry is made in this way, using sun-dried Pedro Ximénez grapes (see our How is Fortified Wine Made page to find out more).

Another key method for concentrating the sugars is to take advantage of mould, known as ‘noble rot’ or ‘botrytis’, that attacks healthy grapes on the vine. Noble rot weakens the skins, therefore speeding up the process of evaporation from the grape flesh and causing the fruit to shrivel rapidly. The rot adds its own unique set of flavours to the wine and needs very specific conditions to grow successfully, therefore only tends to be used in more premium sweet wines, such as Sauternes and Beerenauslese. The mould also doesn’t attack bunches evenly, so the very best sweet wines made in this way need to use grapes that have been individually picked from the vine by hand.

The final method for concentrating sugars in the grapes is to leave the fruit on the vine for a much longer period than usual, and harvest the grapes in winter. The water in the grapes freezes in extreme weather conditions, so picking and crushing them in this condition means ice crystals can easily be removed, leaving an intensely concentrated sugary grape syrup. Because the juice has been made from healthy grapes (rather than grapes attacked by rot), these wines taste pure and flavours are pronounced. Wines made in this way are called Eiswein in Germany and Austria, or Icewine in Canada.

Method 2: Adding Sweetness During Fermentation

Another way of producing sweet wine starts with grapes which have been grown, harvested and crushed in the normal way, however the fermentation is interrupted to ensure grape sugar survives the process (which usually completely gets rid of all sugar).

As we know, yeast converts grape sugar into alcohol and carbon dioxide. If you remove the yeast, fermentation will stop and sugar will remain in the blend. A simple way of doing this is by using a fine filter to remove yeast from the fermentation tank before the process has had a chance to finish.

The more well-known technique for interrupting fermentation which you may have heard of is fortification. Yeast naturally dies at 15% ABV, so fortification is when the winemaker poisons the yeast by adding sulfur dioxide or more alcohol into the blend. Port is a famous fortified wine made in this way.

Method 3: Adding Sweetness After Fermentation

The final option winemakers have for producing a sweet wine is to add a sweet component to the wine after fermentation has taken place.

It’s completely against the rules to simply add sugar, but there are naturally sweet liquids, such as unfermented grape juice, that can be mixed into the wine instead. Some sweet wines, such as Cream, Pale Cream and Medium Sherries, are made by taking a dry Sherry and adding sweet alcohol (PX Sherry) into the mix.