SWEET WARS: THE FRUCTOSE STRIKES BACK
A dessert wine primer…
For discussion purposes:
1.0 g/L = 0.1% Residual Sugar
(weight/volume measurement here, not weight/weight (which is what Brix is))
1.0 degree Brix = 1.0% Dissolved Solids (largely glucose + fructose, weight/weight measurement)
It’s important to know that degrees Brix does not directly correlate to percent of residual sugar, though they are very close in most finished wine applications. The issue is that we have to label the wine with the same measurement type for the pre and post labeling to qualify as late harvest.
There are essentially four main categories of traditional dessert wine:
- Late Harvest
- Ice wine
- Fortified Dessert Wines (i.e. sweet Port)
- Botrytized (i.e. Sauternes)
The vast majority of dessert wines fall into one of these four categories.
The major outliers being wines that are intentionally stopped sweet but also with relatively low alcohol (though these aren’t really considered dessert wines in my experience, just sweet or off-dry table wines), and the very few and rare non-late harvest wines that are ahem forced into higher sugar content via practical methods (like our Meeker Frozin, which is to my knowledge one of the only non-late harvest dessert wines in the world with a starting ferm brix of over 35, but that’s a different story for a different day).
Here’s the thing though: All three of the latter categories are frequently made from late harvest fruit. Late Harvest is the catchall term for wines made from fruit that has been left on the vine until the vine stops developing the fruit and essentially gives up on it. The fruit begins to raisin on the vine and is picked some point thereafter. Most dessert wines of any category have seen some late harvest time (the exceptions usually being fortified wines, which vary in style and method greatly and are far too varied to summarize). Late Harvest wines can vary anywhere from 10-18% alcohol and can have residual sugars as high as 10+%. It’s all a matter of how much sugar the juice started with and how and when it was stopped during fermentation.
Ice wine is made from grapes that are left on the vine until a hard freeze, at which point they are pressed while still frozen, the ice in the grapes is left behind in the press, thus further concentrating the sugar content. Ice wine has to be made according to government regulated standards of minimum sugar content depending on the country. The wines are typically lower in alcohol compared to most dessert wines and very, very sweet (>100 g/L RS).
Fortified wine is a little more complicated. Not all fortified wines would be colloquially reffered to as dessert wines, because not all fortified wines are sweet, even though the usual American exposure to fortified wines is the vast majority of them are sweet (50+ g/L RS).
Port, for example, is made in sweet and dry variations, the sweet being far more common in the US. There are other fortified wines that, while often sweet, wouldn’t necessarily be called dessert wines unless you’re talking about the sweetest versions (i.e. the many kinds of Sherry, but Sherry is typically not late harvest).
Anyways, fortified wine, by definition, is wine that is fortified with a distilled spirit (usually brandy) to halt the fermentation and increase the alcohol (which makes the wine stable by killing the yeast and creating a far more inhospitable environment for yeast). In terms of California “Port-style” wines, this is frequently done with late harvest fruit, or at the very minimum fruit picked well after typical picking windows (even as those have become late with the style evolution of CA wines). Port and port-style wines are typically 18-22% alcohol with varying levels of residual sugar.
Botrytized wines are made from fruit that has been left to rot on the vine from Botrytis cinerea, colloquially known as “noble rot”. The nature of this necrotrophic fungus essentially damages the skin of the berries while still on the vine, allowing them to concentrate from a dehydration process more quickly. This is essentially late harvest, because if you’ve got bad botrytis issues and you wanted to make table wine, well, you’re too late (dealing with small levels of botrytis in making regular wine is pretty typical and not too much of a curveball). These wines are frequently 70-100 g/L RS and sub 14% alcohol.
And then, like I said, there are outliers.
The main issue with dessert wines is that, at least traditionally, they had to be at least largely bottle stable or else they would continue to ferment to dryness. This stability (meaning it won’t continue to ferment past a given target alc/sugar balance) can be caused by multiple factors.
Fortifying the wine increases the alcohol high enough to make it stable. High enough levels of residual sugar, believe it or not, can also create a stable environment (yes, sugar can act as a preservative, essentially, long story don’t feel like typing that out today). Lastly, the wine can be made largely stable by adding sulfur to kill the yeast, though that’s not always 100% effective.
But then there was this wonderful invention called the sterile filter that allowed wines that are not chemically bottle stable to be made bottle stable because they can be bottled in a way that prevents any yeast or bacteria for making it into the bottle to cause a problem (for those curious: sterile filters for the purposes of wine are 0.45 micron absolute). The sterile filter allows wines of all kinds (including normal wines) to go to bottle without being fully re-fermentation stable, which is why the sub 1.0% residual sugar on table wines thing is now so incredibly common place (worth noting whether a wineries dry wines are sterile filtered or not… ours are not, but ours are also fully dry).
Anyways, the sterile filter allows us to essentially stick the wine where we want it with a sulfur addition as they do with German sweet or off dry wines, then bottle it without concern of traditional bottle stability or refermentation problems. This allows us to make a wine like this that is not fortified, but also not incredibly high alcohol.
So yeah, dessert wine. It’s made a bunch of different ways resulting in a bunch of different alcohol/sugar combinations. Hard to talk about any of them with sweeping generalizations as I think I’ve successfully demonstrated here.
TL;DR You start with a given concentration of residual sugar, you convert some of it to alcohol, and then you stop it with one of a few different techniques. The different techniques to achieve the starting sugar content and the different techniques to stop the fermentation are what define a dessert wine.