Sweet wines are becoming more popular among serious wine drinkers and it’s easy to see why, the quality has sky rocketed in recent years and the evolved sweet-tooth is ever present. However sweet wines are made using several different methods. Yeast converts sugar to alcohol and for almost all wines, red or white, the fermentation continues until no detectable sugar remains. However if you want to keep a little sweetness in the wine, interrupting the fermentation is a tried and tested method. Other methods include adding a sweet component and for the odd exceptional wine the sugar levels in the grape are high enough that the sugar remains in the finished wine.
Yeasts die when the alcohol level reaches 15% abv. So if the yeast dies at 15% abv, there is nothing to convert the remaining sugar to alcohol, hense some of the sugar will remain in the finished wine. There are many many options for concentrating the sugar levels in the grape, including drying and freezing the grape and taking advantage of Noble Rot (Botrytis Cinerea). Noble rot is a mould which attacks healthy, ripe grapes. It weakens the skin , speeds up the evaporation of the water which causes them to shrivel. However it also concentrates the sugars and the acids, while at the same time adding it’s own flavours. This method is very popular with wines such as Sauternes, Tokaji and German Beerenauslee.
Conditions need to be perfect to create these wines, a problem-free ripening period is vital to produce fully ripe, healthy grapes. Damp and misty mornings encourage the growth of the mould, so those rolling fogs that come in and look ultimately refreshing are vital. Warm afternoon sun will dry the grapes out, resulting in the perfect conditions. Unfortunately very few wine regions in the World experience these conditions and it cannot be relied on every single year, so when you get a good year, you want to snap up as many bottles as you possibly can.
Winemakers have several choices when it comes to the method they use, and several choices within the chosen method. For example, we alluded to the fact that drying the grape is a common method for sweet wines. The winemaker can choose to dry the grapes on the vine by harvesting them a little later than usual, or they can pick the grapes and then dry then in a well ventilated area that encourages evaporation.
So how do you actually create sweet wines with the fermentation interruption method, in truth it is surprisingly easy.
As mentioned earlier, yeast converts sugar to alcohol. If the yeasts are stopped before they can convert all the sugar to alcohol, a sweetness will remain in the finished wine. A fine filter can be used to remove all the yeast from the liquid, or the yeast could be poisoned, which sounds far more dramatic than it really is. To poison the yeast you add sulphur dioxide or alcohol midway through the process, resulting in a beautifully sweet wine.
One question we’re often asked is, can’t you just add sugar to the wine to make it sweeter? The answer is, no! Adding sugar to the wine to improve it’s sweetness is not permitted. However adding sweet liquids is absolutely fine. For example, you can add unfermented grape juice to sweeten the wine, as it hasn’t undergone the fermentation process, it still retains its sweetness.
If you’ve never tried a sweet dessert wine, then you really should give it a chance. I was reluctant at first, but matching a dessert wine with the post roast cheesecake is a lovely alternative to the after dinner coffees. My personal favourite comes from one of our favourite producers, Nicola Allison at Chateau du Seuil. The 2012 Cerons which derives from a vineyard situated on the right bank of the Garonne, is pure luxury, organically produced by a Welsh couple in the heart of Bordeaux.