What do Port, Moscato d’Asti, Sauternes, Alsace’s Vendange Tardive, Passito and Icewine have in common? They are all sweet wines – although vinified in different ways. In this article, I explore the various styles of sweet wine, their production and taste profiles

If you, like me, have a sweet tooth, I bet you love sweet wines. Inexplicably, some connoisseurs look down on people that openly profess their love affair with sweet nectars. I don’t know where this tendency comes from. Of course, I don’t share such prejudice.

Sweet wines can be gorgeous, complex and mesmerising as any other style. In fact, some of the most exhilarating wines I have ever tried are indeed sweet: Vintage Ports, Alsatian Sélection de Grains Nobles or luscious Sauternes – to mention a few examples.

In this article, I will explain how sweet wines are made, outline their vinification process and give some examples of each production technique. Without further ado, let’s delve into this sweet vinous paradise!

Introduction

In a standard winemaking process, during fermentation, yeasts consume the sugar found in the grapes and convert it into alcohol. When roughly all the sugar is converted into alcohol you get a dry wine. Regardless of how they are produced, all sweet wines share a common feature. The final drink has a predominantly sweet taste as the wine retains some unfermented sugar.

As I explained in a previous article, when it comes to sweetness, wines can be classified as bone dry, off-dry, medium-dry, medium-sweet and sweet. The amount of residual sugar (which is the unfermented sugar left in the finished wine) increases as you move along the sweetness spectrum. A wine is referred to as sweet when sugar is its prominent feature. In technical terms, wine featuring more than 80-90g/l of sugar would be considered sweet.

Generally, sweet wine can be made in the following three ways:

1. adding a sweetening agent to the finished wine
2. stopping fermentation partway through the winemaking process
3. concentrating the sugar content in the grapes

I will go through each of the three aforementioned methods in detail. Before we get into the geeky nitty-gritty, here’s an infographic which summarises all the techniques used to vinify sweet wines.

Adding a sweetening agent

Some inexpensive sweet wines are made by adding a sweetening agent to a finished dry wine. In those circumstances, you need to ensure that the added sugar will not ferment. The winemaker prevents fermentation of the added sugar through filtration and sterilisation (typically by adding sulphur oxide) before bottling.

There are different types of sweetening agents that can be added to make this kind of sweet wine; they consist of one of the following:

• sweet reserve, this is a preserved grape juice
• grape concentrate (called süssreserve in Germany) made from fresh grape juice by removing its volatile elements
• Rectified Concentrated Grape Must (RCGM), created by treating grape juice to remove water and reduce the concentration of solids other than sugar

Wine Style – As far as style is concerned, sweet wines made with the sweetening agent method tend to be high-volume and simple. They don’t have the intensity and depth of the more refined sweet wines made with other techniques.

Wines to try – Sweet wines using the sweetening agent method include Liebfraumilch and other German bulk sweet wines (made using süssreserve), and some cheap versions of Marsala, Sherry and Malaga wines.

Stopping fermentation

The key concept of this approach to sweet wine production is to halt the fermentation process before all the grapes’ sugars have been converted into alcohol. As a result, the final wine will retain some sugar content.

There are three ways of stopping the fermentation:

• fortification
• adding a high dose of sulphur oxide
• removing the yeasts by chilling and filtering the wine

Fortification

Fortification is the process of adding spirits (often grape spirits) to the wine during or after fermentation. Where fortification takes place after the wine has been fully fermented, these wines will not be sweet. For example, most Sherry is dry. Sweet wines are obtained when fortification takes place during fermentation. The high alcohol content of the fortified solution kills the remaining yeasts, creating a stable sweet wine.

Two factors that affect a fortified wine style and taste are:

• the stage at which spirit is added to halt fermentation. The earlier spirit is added, the sweeter the resulting wine
• the nature (and quality) of the spirit used. The sources of spirit used include grape (the most common), cane sugar, sugar beet or other agricultural products. Local regulations dictate the type of spirit allowed for each wine denomination

Wine Style – Adding a high-alcohol spirit alters the structural components of the wine. As a consequence, fortified wines are fuller in body, warmer and richer than their non-fortified counterparts. 

Due to the added spirit, fortified wines are always more alcoholic than traditional dry wines. The exact alcohol content depends on the specific style. For example, Port wines range from 18 – 20 % abv, while most Vins Doux Naturels average around 15 – 16 % abv. 

Due to their high alcohol content, fortified wines are usually sturdy and resilient. Generally, fortified wines age well and don’t spoil easily. For example, most Madeira wines are virtually indestructible!

Wine to try – Examples of fortified sweet wines include:

• Port (all port styles), a red dessert wine made from a blend of Portuguese black-skinned grapes including Touriga Nacional, Touriga Franca, Tinta Barroca and Tinto Cão. The wine’s characteristics vary a lot depending on the specific Port style
• Medium and Cream Sherry consist of a fortified wine base with the addition of Pedro Ximenez or grape must. See my Jerez and Sherry series for further info about Sherry.
• Madeira (especially the Boal, Malvasia and some Tinta Negra styles) are intensely concentrated wines with raisin and caramelised aromas balanced by a great acidity
• Vins Doux Naturels (VDN): many sweet wines carry this designation, especially in the South of France. For example:
  • Banyuls (made predominantly from Grenache and originating from the slopes of the Pyrenees in Roussillon)
  • Maury Doux (also from Roussillon and is found in different styles and can be made from both white and black-skinned grape varieties)
  • Rasteau (from the Rhone Valley and made mainly from Grenache)

VDN vary in style. However, they are commonly high in alcohol, have a great body and usually present a good concentration of flavours.

• Fortified Muscats (such as Muscat de Beaumes-de-Venise, Muscat de Rivesaltes, Moscatel de Setúbal or Australian Rutherglen) are similar in style to VDNs but also retain the typical aromatic characteristics of the Muscat varieties.
• Marsala (a fortified wine from north-western Sicily), can be made both from white (Grillo, Damaschino) or black-skinned grape varietals (including but not limited to Nero d’Avola, Perricone and Nerello Mascalese). Marsala has many sub-styles and quality varies a lot. Some Marsala wines are even dry or off-dry.

Stopping fermentation by adding sulphur dioxide

The fermentation can also be stopped by adding a generous dose of sulphur dioxide (SO2). The substance is toxic to yeasts and ends up killing them.

Wine Style & Wines to try – The sulphur dioxide method of producing sweet wine is often seen in inexpensive sweet French wine. They are generally low in alcohol (around 11 % abv) and are simple in taste.

Stopping fermentation by chilling and filtering

A third method to stop fermentation is to chill and subsequently filter the wine. Reducing the temperature inhibits the sugar-to-alcohol conversion operated by the yeasts. Afterwards, filtration is aimed at chemically removing the remaining yeasts and thus halting fermentation.

Wine Style – The sweet wines produced by the chilling and filtration method are low in alcohol and light in body. They usually preserve the aromatic characteristics of the original grape varieties.

Wines to try – German Kabinett and Spatlese wines are produced following this approach (even though these are not technically sweet wines, but rather medium-dry or medium-sweet). Moscato d’Asti is also vinified using this process. The “Asti Method” envisages fermenting the must in pressurized tanks, then stopping the fermentation by chilling and filtering when the alcohol level reaches around 5 or 6 % abv.

Concentrating the sugar content in the grapes

Many of the best sweet wines are produced by concentrating the sugar content in the grapes before the start of the fermentation process.

The founding principle of this approach is to remove water from the grape so that everything else becomes more concentrated (sugar, acids, flavour compounds). An environment extremely rich in sugar is not an ideal environment for yeasts. The combined effect of the alcohol produced by partial fermentation and the high quantity of sugar inhibits further yeast activity. The resulting wine still has decent alcohol content as well as a noticeable residual sugar.

There are several ways to achieve a high concentration of sugars in grapes. Each method produces a different style of sweet wine. The main concentrating techniques are:

• Noble Rot
• Drying the grapes on the vine
• Drying the grapes after harvest
• Freezing the grapes on the vine

Noble Rot

Botrytis cinerea is a fungus that affects many vegetables and fruit including grapes. Botrytis cinerea can be a blessing and a curse for winemakers. Under undesirable and constantly humid conditions, this fungus causes grey rot, a harmful condition that can destroy crops.

Under the right conditions (humid misty morning followed by dry and sunny afternoons), magic happens. The fungus punctuates the grapes without causing too much damage. Through these puncture wounds, water evaporates, concentrating sugar, acids and flavours inside each grape berry. This condition – sought after by winemakers – is called Noble Rot. Wines produced this way are known as botrytized wines.

For a couple of reasons, botrytised wines are usually expensive. First, the effect of Botrytis cinerea is not uniform so it doesn’t affect all grapes and/or bunches in the same way. Noble Rot only occurs in what were originally perfectly healthy grapes. Furthermore, a thorough and selective manual harvest is required to pick the right individual grapes. Sometimes several pickings are required to select optimal berries each time. Secondly, the ideal conditions for Noble Rot may not happen every year nor in every corner of the vineyards at the same time.

Wine Style – Since Botrytis cinerea adds its own signature flavours to the grapes, wines made with Noble Rot exhibit characteristic aromas of honey, apricot, candied citrus and a resinated quality. To complete their wine profile, botrytised sweet wines usually have a luscious full body and an extreme intensity of flavours balanced by high acidity.

Wines to try – Famous sweet wines produced with Noble Rot include:

• Sauternes and Barzac (from the Left Bank of Bordeaux, France), made from blends of Semillon, Sauvignon Blanc and Muscadelle.
• Monbazillac, an Appelation d’Origine Controlee (AOC) for sweet white wines on the Left Bank of Bordeaux. A similar in style, more affordable alternative to Sauternes but normally simpler and less concentrated.
• Tokaji (from the Tokaj district in eastern Hungary), made from Furmint-dominated white blends – a decadent dessert wine marked by a refined high acidity. Aromas include candied citrus, apricot, honey and flowers.
• Beerenauslese and Trockenbeerenauslese are wines from Germany and Austria. They are extremely concentrated and aromatic sweet wines that can be made from a few selected grape varieties (those made from Riesling are the best specimens). The grapes are late harvested (see below) and the resulting wines are rare and costly.
• Sélection de Grains Nobles (SGN) are wines from Alsace that are made from one of the noble Alsatian varieties (usually Riesling) in a similar fashion to Trockenbeerenauslese.
• Coteaux du Layon, Quarts de Chaume and Bonnezeaux are three AOCs for sweet white wines in the Anjou district of the Loire region. They are considered some of the best French dessert wines. These wines are smooth with crystalline acidity and made entirely from the Chenin grape variety.
• Riverina originates from New South Wales, Australia where they are famous for some notable botrytised wines made from the Semillon grape. These dessert wines are golden-hued and are infused with intense marmalade, honeysuckle and floral aromas.

Apart from the appellations and regions mentioned above, there are other wines (both sweet and dry) that can be made with a variable proportion of grapes affected by Noble Rot. These wines exhibit some botrytized features but to a lesser degree such as a slight raisin character or honeyed undertones. More often than not, the presence of botrytis is not even mentioned on the wine label.

Drying the grapes on the vine

Another popular method to concentrate the sugar level in the grapes before fermentation is to leave fully ripe bunches on the vines well past the normal harvest time. While these grapes are left hanging on the vine, they dehydrate and turn to raisins which concentrates the sugar, acidity and aromatic compounds. This approach to producing sweet wine is called late harvest or passerillage (in French). 

Wine Style – Wines made through the late harvest method feature a mellow and overripe fruit character (fruit aromas are intense and include macerated and dried fruit flavours and/or tropical fruit in whites), with a full body and rich mouthfeel. These wines usually boast a high acidity.

Wines to try – Examples of late harvest wines include:

• Alsatian Vendange Tardive (TD) wines are made from one of Alsace’s noble grape varieties
• Some German Spätlese and Auslese wines can be made from a few grape varieties but most notably with Riesling
• Vin de Constance, the legendary dessert wine produced in the Western Cape district of South Africa; it’s made from the Muscat Blanc à Petits Grains grape
• Many Italian dessert wines are labelled as Vendemmia Tardiva (which literally means “late harvest”)

The Late Harvest indication on a wine label usually denotes a sweet wine, but that’s not always the case. Occasionally, Late Harvest wines can be dry or off-dry, which means that their fermentation phase was extended to convert more sugar into alcohol. It’s important to know the specific wine characteristics to avoid surprises.

Sometimes winemakers adopt more than one vinification method to accrue sugar. For example, botrytised wine can be also made from late-harvested grapes. In these circumstances, the final wine shows characteristics of both approaches.

Drying the grapes after harvest

This technique is similar to the late harvest method. The key difference is that grapes are dried after harvest. Healthy and fully mature grapes are picked and left to dehydrate under dry and warm conditions. A slight variation of this method (used for example in some Italian regions) is to twist the stalks and leave the grapes on the vines. In such cases, the berries do not receive further nutrients, so this is another difference from the aforementioned late harvest approach.

The common name for this technique is appassimento, which literally means “withering” in Italian. Dessert wines produced this way are called passito.

 For this technique to succeed, grapes must be healthy and have intact skin to avoid mould or rot. Therefore, it’s common to have a careful fruit selection before the drying of the grapes. Other important concerns include air circulation and dry conditions. Each factor increases the price of production. Therefore it will come as no surprise that great passito wines are relatively expensive.

The grapes for passito wines can be sun-dried over an extended period of time (this is typical in warmer climates) or air-dried in winery lofts. Some producers also use artificial interventions such as temperature control and wind machines, which usually result in less interesting wines.

The duration of the drying process depends on many factors, including grape variety, desired wine style and climatic conditions. Typically, the colder the region, the more time is required. Drying time can range from three weeks to six months.

Wine Style – Passito wines have a full body, feature raisin flavours and are normally high in alcohol. The aromas are bold and concentrated, usually enhancing and developing further the original aromatic characteristics of the source grape varieties.

Wines to try – Some famous wines produced with the appassimento method include:

• Rectioto della Valpolicella (Veneto, Northern Italy) is usually made from a blend of black-skinned grape varieties including Corvina, Corvinone and Rondinella. It’s intensely sweet and usually fruit-driven, with great concentration and macerated fruit flavours 
• Picolit is made from a white grape variety local to the Friuli region of Northeast Italy. It’s commonly associated with passito wines displaying characteristic apricot flavours.
• Vin Santo del Chianti (Tuscany) is made from a blend of mostly Trebbiano Toscano, Malvasia and other local grape varieties. It’s a dessert wine made in an oxidative style, featuring a characteristic rancio aroma, along with nutty and sultana flavours. In Italy, you can also find “vin santo” from other regions. The wording is not normally regulated in the appellation system. As a result, generic vin santo’s traits and quality can vary a lot from case to case
• Passito di Pantelleria (Sicily, Southern Italy) is a luscious wine made from the Muscat of Alexandria grape (known in Sicily as Zibibbo).
• Primitivo Dolce Naturale (Puglia, Southern Italy) is the sweet version of the popular Primitivo originating from the heel of the boot. It is fruit-forward, textured and warm on the palate with intense flavours.
• Vinsanto (from the Santorini island of Greece) is made mainly from Assyrtiko blended with Athiri and Aidani. Similar to Vin Santo del Chianti, Vinsanto has more stringent appellation rules.
• Samos Nectar (from Samos, a Greek island in the eastern Aegean Sea) is one of the finest Greek dessert wines. Made from the Muscat Blanc à Petits Grains grape, this wine exhibits aromas of raisins, dried fruits, honey and dried nuts.

As you can see from the list above, Italy produces more dried-wine wines than any other country. There are countless passitos in Italy, at least one for every region. 

Some air-dried wines are dry or off-dry, such as Amarone della Valpolicella, the famous bold red wine from Veneto. However, if you see the word “passito” on the label, almost certainly it’s a sweet wine. 

Freezing the grapes on the vines

Lastly, another method to concentrate sugar in the berries before fermentation consists in leaving healthy grapes hanging on the vines into the winter months. When the temperature goes below zero degrees, the water inside each berry turns into ice. That’s when harvest takes place. Upon fruit reception in the winery, grapes are pressed separating the ice (which remains in the press) from the free-run liquid. Deprived of water, the pressed grape becomes more concentrated in sugar.

Sometimes the aforementioned natural process can be replicated via cryoextraction, a fancy word which means artificially freezing the harvested grapes in the winery.

Wine Style – Wines made following this technique display a pure varietal character, with a predominance of primary flavours. These wines are usually not high in alcohol and thanks to their very high acidity are extremely refreshing.

Wines to try – Some examples of sweet wine obtained by freezing the grapes on the vines are:

• Eiswein (produced in many central and north European countries, mainly Germany, Austria and Luxembourg), made from white wine grape varieties, typically Riesling. The best examples of Eiswein can bear a hefty price tag.
• Icewine (from Canada, Oregon, and Michigan) can be either white (made from Riesling or Vidal, a hybrid grape variety) or red (made usually from Syrah, Cabernet Sauvignon or Cabernet Franc).

Conclusion

Sweet wines can be made in various ways. Even though sweet wines share some common attributes (notably the predominance of the sweet taste), they can significantly differ in style, flavour profile and other characteristics. 

In my article, I went through each technique used to vinify sweet wine. I detailed how the different approaches work and how they determine the characteristics of the finished wine. I also gave examples of famous sweet wines made by each method.

Hopefully, my article dedicated to sweet wines gave you an overview of what the luxurious world of sweet nectars can offer. The next step would be, of course, to try some dessert wines. If you need guidance on how to enhance your tasting experience, why you don’t give a look at my previous article How to taste wine, and why we should bother? Above all, follow your taste buds… They will be in for a treat!

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