Sweetening homemade wine is easy but if done incorrectly can lead to carbonated wine, blown off corks, or worse... blown up bottles and a huge mess. Most classical red wines do not need any form of sweetening but wines made from fruits, native grapes, or white grapes often need additional sugar to achieve balance. Without any form of sweetening, these high acid wines can come across as sour and difficult on the palate.
Why Some Wines Taste So Good Dry
Red wines generally have a pH in the 3.5 to 3.7 range and contain little or no malic acid due to a process called malolactic fermentation, where anaerobic bacteria convert malic acid into much softer and buttery lactic acid and diacetal. In these big bold wines, oak tannin, grape tannins, and anthocyanin (a color contributor) can polymerize forming long molecules that contribute to a silky mouth feel without any added sugar. Additionally, the higher alcohol of a traditional red wine can add a sensation of sweetness on the tongue. These factors combined are why a red wine can be bone dry (0.0% residual sugar) yet very approachable and balanced tasting.
Why Some Wines Need Sugar
White, fruit, and native grape wines are often significantly more acidic (pH 3.0-3.5) and generally are not encouraged to go through malolactic fermentation, so their malic acid remains. Malic acid in the absense of sugar tastes harsh like sour apples or those warhead candies that you had as a kid. To make things worse, the lower tannin of these wines often leaves them feeling thin after fermentation runs dry. With a little sugar though, the fruit flavors come to life, the malic acid tastes fruity, the mouth feel lingers around and the wine tastes balanced and refreshing. There is no one-size-fits-all answer as to how much sugar is needed, as every wine is unique and every taster has different preferences but with some bench trials, you can dial your sweetness level right where you want it.
How to Sweeten Your Wine
There are two common methods of creating a wine with residual sugar. These include back sweetening and cold crashing. With either method, it is important that you take measures to assure that the wines are stable before bottling. If the wines are not stable, the fermentation can kick off again, meaning the yeast will consume the sugar, create more alcohol and CO2 and you will be in the midst of friendly fire with corks blowing by you and wine spraying like old faithful. The aftermath will look like a scene from Law and Order SVU and you will have quite a cleanup on your hands, so make sure you take measures to assure that re-fermentation does not occur! (See step 3 below)
Method 1: Back Sweetening
Back sweetening is the easier of the two methods and can achieve great results. Simply put, back sweetening is the process of allowing your wine to ferment to complete dryness, stabilizing, and adding some form of sugar before bottling.
The winemaking process for back sweetening is unchanged until just before bottling and goes as follows:
1. Ferment as usual
2. Rack several times over several months until the wine is crystal clear and there is absolutely no sediment on the bottom of the carboy. This is very important! Any haze or sediment may contain yeast cells that are hungry for the sugar that you will soon be adding. If the wine does not clear within six months, consider using fining agent like bentonite or super kleer to encourage remaining particles to drop out of suspension, then rack off the sediment.
3. Take measures to assure that re-fermentation does not occur and the wine is stable. The easiest method for home winemakers would be to add potassium sorbate (1/2tsp per gallon) and a dose of potassium metabisulfate (~1/4tsp per 6gal). The potassium sorbate will stop any rogue yeasts from multiplying and the potassium metabisulfite will fight oxidation and help stop any rogue undesired bacteria from feeding on the sugar. The other option here is to run the wine through a sterile filter (<.5micron) and add potassium metabisulfite. If done properly, this will filter out enough yeast that it will not be able to re-ferment.
4. Add sugar. The preferred method of adding sugar is to make a solution of invert sugar by simmering a 1:1 mix of table sugar and water with a pinch of citric acid for about 20 minutes. This will break the sucrose molecule into fructose and glucose which will inevitably happen in the wine over time due to the acidic environment. If you invert the sugar before adding, it is easier to gauge how much to add and the perceived sweetness will not change much over time. Take this solution and slowly add it to your stabilized wine and taste as you add. Add until the wine is almost as sweet as you would like it, then chill a small sample. Taste the chilled wine, and add more invert sugar if necessary. Try not to get too tipsy in this process. When finished, take a hydrometer reading and mark it in your notes.
5. Allow the wine to sit 3-5 days in the carboy and watch the airlock to assure that no bubbles are occurring.
6. Bottle and enjoy!
Method 2: Cold Crashing
This is the method that many wineries will use but involves more specialized equipment, like jacketed tanks or large refrigerator units. It is the preferred method if more fruity aromas and tastes are desired but watch out for hydrogen sulfide! This method can stress the yeasts, causing them to release hydrogen sulfide (rotten egg smell) which can be very troublesome and difficult to remove. If not addressed, it can lead to worse problems.
1. Decide how much alcohol you want and how sweet you want your wine to be. If necessary, add some additional sugar before fermentation. With this process, the wine will not ferment dry, so your final alcohol will be the difference between the potential alcohol reading on the hydrometer and wherever you stop the fermentation. Another way to calculate is is Original Gravity - Final Gravity x 131
2. Choose a yeast that is not too aggressive and intended for white or fruit wines. Lalvin EC1118 is very hard to stop! Consider yeasts that produce little to no hydrogen sulfide, like those from Renaissance. Pitch the yeast and start the fermentation.
3. Monitor the fermentation and and taste occasionally. Do not use too much yeast nutrient or it will be difficult to stop.
4. When the must reaches the desired level of sugar (Or just before), cold crash the must by cooling to 28°F to 35°F. I use an old refrigerator that I can turn to the highest cooling setting and achieve temps below 30°F.
5. After 5-10 days, rack the wine off the settled yeast and place back in the refrigerator at 28°F to 35°F. Rack and repeat until the wine is crystal clear.
6. Take measures to assure that re-fermentation does not occur and the wine is stable. The easiest
7. Add additional sugar in the form of invert sugar if necessary (See step 4 of back sweetening).
8. Allow the wine to sit 10-15 days in the carboy at room temperature and watch the airlock to assure that no bubbles are occurring.
9. Bottle and enjoy!
Summary
Sweetening can convert an un-drinkable wine into a sensational wine. It is an invaluable tool to have in your tool chest. The main secret is to make sure that those ambitious little yeast cells do not start multiplying in the presence of a healthy meal of sugar. With sterile filtration or potassium sorbate and a crystal clear wine, you should have no issues bottling a sweet wine.
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