Typical mechanism

The typical process involves the addition of alcohol to the must

Must

Must is freshly pressed fruit juice that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace; it typically makes up 7%–23% of the total weight of the must. Making must is the first step in winemaking...

so that the fermentation

Fermentation (wine)

The process of fermentation in wine turns grape juice into an alcoholic beverage. During fermentation, yeast interact with sugars in the juice to create ethanol, commonly known as ethyl alcohol, and carbon dioxide...

 process is prematurely stopped. Most yeast dies when the alcohol content in their environment is raised to approximately 13-15%. By stopping the fermentation of sugars, a sweet taste of the wine

Wine

Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...

 is achieved. This technique is used to make port wine

Port wine

Port wine is a Portuguese fortified wine produced exclusively in the Douro Valley in the northern provinces of Portugal. It is typically a sweet, red wine, often served as a dessert wine, and comes in dry, semi-dry, and white varieties...

 and other sweet wines with high alcohol content.

Types of mutage

Two types of mutage are sometimes distinguished. A distinction being made between adding alcohol to the must before fermentation and adding during fermentation.

1. mutage sur grain:where the mutage takes place during maceration
   Maceration (wine)
   Maceration is the winemaking process where the phenolic materials of the grape— tannins, coloring agents and flavor compounds— are leached from the grape skins, seeds and stems into the must. Maceration is the process by which the red wine receives its red color, since 99% of all grape juice is...
   
    on the skins. This is described as mutage on the cap of the marc and produces vin de liqueur
2. mutage after the traditional maceration and pressing producing vin doux naturel.

Noted wines referred to as having been made by mutage

Reds

• Banyuls AOC
  Banyuls AOC
  Banyuls is a French appellation d'origine contrôlée for a fortified apéritif or dessert wine made from old vines cultivated in terraces on the slopes of the Catalan Pyrenees in the Roussillon county of France, bordering, to the south, the Empordà wine region in Catalonia in Spain.The AOC...
  
  
• Maury
  Maury AOC
  Maury is an Appellation d'Origine Contrôlée for wines made in the Roussillon wine region of France. Almost all wines are red, made from at least 75% Grenache Noir grapes. Other permitted grapes are Grenache Blanc, Grenache Gris, and Macabeu, Malvoisie and Muscat. Maury is well-known for its sweet,...
  
  

Whites

• Muscat de Beaumes de Venise AOC
• Muscat de Rivesaltes
  Muscat de Rivesaltes AOC
  Muscat de Rivesaltes is an Appellation d'Origine Contrôlée for fortified wines made in the Roussillon wine region of France. They are similar to Rivesaltes AOC wines, except for the grape varieties used...
  
  
• Muscat de Frontignan

Other techniques

Other techniques for making sweet wines exist such as vendange tardive

Vendange tardive

Vendange tardive means "late harvest" in French. The phrase refers to a style of dessert wine where the grapes are allowed to hang on the vine until they start to dehydrate. This process, called passerillage, concentrates the sugars in the juice and changes the flavours within it...

, the noble rot

Noble rot

Noble rot is the benevolent form of a grey fungus, Botrytis cinerea, affecting wine grapes. Infestation by Botrytis requires moist conditions, and if the weather stays wet, the malevolent form, "grey rot", can destroy crops of grapes...

, various filtration techniques or early heating of the must, and adding sweet musts after fermentation.