Introduction to Dessert Wines
I thought this week could be interesting to start talking about Dessert Wines and how they are produced. First of all, why are they called “dessert wines”? If you have read our wine and food pairing guide, you will probably know that one of the rules to pair a dessert with a wine is to make sure that the wine is always sweeter than the dish you are serving. Since most of the desserts are usually sweet, we know for sure that most of the wines served with them will be therefore sweet too. You will be surprise to know how many styles and types exist, which makes this specific category absolutely fascinating, but also very confusing if not approached with the right knowledge. One of the first things we need to understand is how a sweet wine is produced and that is what we will be focusing on today.
Once the grapes are harvested they have a natural level of sugar and acid that depends on many factors including variety, amount of heat and light received during the growing season and last but not least when they were picked. The level of sugar is measured at harvest time with a scale called “Brix”. Most of table wines are harvested between 21 and 25 Brix. This is the natural sugar content that yeast will then transform into alcohol, CO2 and heat. Now if we let the yeast process all of the sugar, we will end with a wine that has absolutely no residual sugar left. If we stop the fermentation process before all the sugar has been processed, the resulting wine will be sweeter than a regular wine. When and how the fermentation process is stopped, determines the level of sweetness and the type of wine. There are two main ways to stop the fermentation.
The first method consists in cooling down the fermenting must under 50° F (10° C). The yeast is active between 50° and 86° F (10°-30° C) so if we bring the temperature below that, it will stop its action and leave the leftover sugar in the wine.
The second method is called “fortification” and consists in adding a neutral spirit (usually brandy) to the fermenting must in order to stop the yeast action. The yeast converts sugar into alcohol until it reaches 18% ABV. After that point, the alcohol level is too high and kills the yeast cells. If a neutral spirit is added and the alcohol level is brought over 18%, the yeast cells die leaving behind unprocessed sugar. The wines produced using this method are called “fortified wines”.
Timing between the start of the fermentation process and when one of these techniques is applied determines the level of residual sugar in the wine. There is an exception to these two techniques that is used in a very specific production method. If you are curious, stay tuned because we will talk about it next week when we will discuss Champagne.