Humans are amazingly inventive when it comes to variations on a theme and sweet wine demonstrates it extremely well. Oddly enough, virtually none of the methods involve sugar additions. When you hear of chaptalization, or sugar additions, the sugar is added before fermentation to boost the alcohol, not the sweetness. In some cases grape juice or sweet wine are added to sweeten dry wine but, when you taste sweetness, it’s quite often unfermented, residual grape sugar. So, in that case the fermentation was stopped before the grape sugar was used up. There are a few different ways to go about it.
First, it’s important to understand how fermentation works. It’s a natural chemical reaction. After the grapes are harvested the winemaker usually adds yeast to get the fermentation started or, in some cases, he relies on wild yeast to get the job done. The yeast consumes the sugar, creating by-products of heat, carbon-dioxide gas and, predictably, a little over half the sugar will convert to alcohol. When the yeast runs out of sugar, it either dies or goes dormant and the fermentation ends naturally. There’s usually a trace amount of unfermentable sugar remaining, but you and I can’t taste it if it’s under about ½ of 1% or less. Completely dry wines are actually drier yet.
Light-style sweet wines
For light, fruity styles, such as Riesling, Gewürztraminer or Muscat that are slightly sweet, there are a couple of common approaches. The winemaker may have let the wine ferment to dryness and then added a little grape-juice concentrate to bring up the sweetness. If he wants the weight of a normal alcohol level, plus the sweetness, that’s the way to go. When our Winemaker, Geoff Gorsuch, makes our slightly-sweet Chenin Blanc he stops the fermentation, by chilling the wine until the yeast goes dormant, before the yeast has used up all the sugar. He keeps the wine cold until he’s able to filter the remaining yeast cells out later. This produces a lower alcohol which is right in step with the delicate style of wine Geoff is looking for. So, in these cases the grapes were harvested at what is considered a normal sugar level, around 21-24%.
If the winemaker wants to start with very sweet grapes, one way is to pick them and dry them. Italy is the country most of us think of when it comes to producing sweet wine this way, such as Vin Santo and Recioto. Of course, the dehydration boosts the sugar content and concentrates the flavors. Wines made this way can vary a great deal in sweetness, quality and character. The famous Amarone is another wine made of dried grapes, but it’s fermented to dryness so it packs a wallop in terms of both flavor concentration and alcohol.
Late harvest wines
Another way to concentrate the sugar is to leave the grapes on the vines longer than normal. This is risky business! These wines are referred to as “late harvest”. Late-harvested grapes make more complex, memorable wines when they are also botrytized – technically rotten. Sauternes, Barsac, Beerenauslese and Hungarian Tokaj are great examples of wine made of what’s called the noble rot. This botrytis cinerea rot perforates the grape skins, which leads to dehydration. Believe it or not, the rot, itself, gives the wine a distinctive honeyed aroma which, once experienced, is never forgotten. Wines that result from “noble rot” tend to have tremendous longevity, so they’re excellent candidates to put away for a 50th anniversary party, or a child’s 21st birthday.
The latest of all late-harvest wine is icewine (eiswein in German), which is made of grapes that are harvested when they’re frozen! This sounds crazy, but pressing them before they thaw allows the winemaker to extract a great deal of sugar and flavor, without much water, so the wines are very sweet and rich – the harder the freeze, the richer and more concentrated the wine. As you can imagine, these wines are not made in any volume. Germany and Canada are the best-known producers of this style. Icewine and botrytized wines are so rich that they’re usually bottled in half bottles. They’re also, understandably, very expensive because production is extremely low in terms of yield per acre and gallons per ton. Not to mention the risk of losing the crop, altogether, while waiting for the conditions to be right for this sort of endeavor.
Many of us think of Port, Sherry or Madeira when dessert wine is mentioned. They fall into a category called fortified wine. The fortification is added alcohol which, in the case of Port and Madeira, is added to stop the fermentation from completing. The alcohol kills the yeast so, if it’s added before the sugar’s all gone, the wine is both sweet and high in alcohol. These wines can live a very long time. Sherry creates confusion because, by nature, it’s a dry wine – the fortification doesn’t come until the wine completes fermentation. But – in some cases the wine is sweetened up later. It’s not uncommon to sweeten dry sherry with sweet, concentrated wine. In Spain, the home of sherry, the sweet wine is made of the Pedro-Ximenez grape. Good quality cream sherry is an example. The wine called Pedro-Ximenez,or PX for short, is reliably sticky sweet, and also quite delicious – the Spanish like to pour PX over their ice cream!
So, that’s sweet wine in a nutshell. Look for more detailed descriptions of each style in the near future. Cheers!