Back sweetening is the process used to turn a completely dry wine into either an off dry or sweet wine. This is just one of many ways in which you can produce a sweet wine.
The most common ways of back sweetening are by adding sugar or unfermented grape juice to a finished wine. By finished I mean fermented and stabilized.
Back Sweetening with Sugar
Often amateur winemakers will add sugar to a fully fermented dry wine to create a sweet wine. While this does work there are issues with the flavors of the wine and sugar.
Because the sugar was not a product of the grape and because it is added after the wine has finished fermenting it doesn’t completely integrate into the flavor profile of the wine. Instead you’ll have a sweet wine where you can actually taste the table sugar.
Aging a back sweetened wine can help integrate the flavor of the wine and the sugar. However, this has its limits. There are many out there that can pick out the table sugar flavors of wines sweetened this way.
Should you want to experiment with this method try it with a single glass of wine at first. Draw a sample glass of wine with a wine thief. Next, add table sugar in very small increments, tasting between each addition.
If you like what you taste then proceed to sweeten your entire batch. If not, consider leaving your wine dry.
Back Sweetening with Unfermented Grape Juice
A more preferable method of back sweetening is to ferment the wine completely dry and add unfermented grape juice to it. This process is known as back-blending.
It works best when the juice used to sweeten the wine has come from the same juice that was fermented to make the wine. This makes for a much more integrated final product.
If you know you want to make a sweet wine from the start reserve a portion of the grape juice for sweetening. After the wine is dry and stable you can blend the unfermented juice back into your wine until it reaches the desired level of sweetness.
When back-blending add the unfermented grape juice in small amounts and taste samples often. It’s a good idea to first try this with a sample glass of wine. After all, you can’t un-sweeten a wine that is too sweet so be careful not to go to far.
Sweet wine kits come with a package of unfermented grape juice pre-measured in the correct proportions for the amount of wine made in the kit. The Riesling kit I made included an “F-Pack” of unfermented grape juice concentrate.
I can say from experience that the f-pack did not negatively affect the flavor profile of the wine. It tastes just as integrated today as it did before I back-blended it.
This is the preferable way to produce a sweet wine at the amateur level. Wineries have more complex methods, however, some wineries do produce sweet table wines by back-blending.
Stability is Key
The most important concern with back sweetening and back-blending is ensuring your wine is stable enough to reintroduce sugar to the mix. Sugar, after all, was the main food source that the yeast fed off of to create the wine to begin with so you’ve got to be sure fermentation won’t begin again if additional sugar is added.
Stability can be ensured through the use of additives or by filtering your wine. Additives such as potassium metabisulfite and potassium sorbate, when used together can prevent further fermentation of the added sugars. Potassium sorbate has its own issues though (read more here).
These additives only work with a completely dry wine though. You can’t stop a fermentation mid stream with these additives. In fact there are no additives for stopping a fermentation because they would be so harsh the wine wouldn’t be consumable afterward.
Filtering is an alternative that allows you to use less additives to ensure stability. While you will still want some sulfites in your wine you will be relying mainly on the filter to remove all the still living yeast cells.
Stop and think about that for a second though. Be filtering you are passing your wine through a medium so fine it can remove single cell organisms suspended in the wine.
A filter this fine is also fine enough to remove flavor, aroma, and color compounds from your wine. Many winemakers don’t like filtering for this reason. It removes character in addition to the yeast.
Photo used under creative common license. Taken by: Gabriele Cantini