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Residual Sugar in Wine

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This issue is misunderstood even by some of the most devoted amateur wine makers that I’ve talked to.  When you make wine, especially fruit wine, you sometimes want to add sugar to the juice before fermentation.  It’s more common than I would have imagined that some of these wine makers believe that this addition of sugar sweetens the wine.  In most cases, it does not.  Sugar is usually added before fermentation to increase the final level of alcohol.  That’s what fermentation is, converting sugar into alcohol and the more sugar you add the more alcohol you will get to a certain point.  Grapes usually have enough natural sugar that you don’t need to add any to get an acceptable alcohol level.

Here’s where it gets confusing.  If you add enough sugar, you’ll get to the point where the alcohol is so high it will kill the yeast.  In this case, there will be sugar left over and the wine will be sweeter.  The left over sugar is called Residual Sugar.  The confusing part is that all wine has some residual sugar, even dry wine.  These dry wines are in the vicinity of about 0.25% sugar.  A sweet wine can be as much as 5% and even higher.  Our 2015 Ice Wine starts out at 36% sugar before fermentation, (all natural), and finishes at 14% residual sugar which is about average for that particular style wine.

The real question in your mind, I’m sure, is “Where does the sweetness come from, if in most cases it’s not the sugar added before fermentation?”  The wine is actually sweetened with sugar just before bottling.   If you add it too early it again will just start fermenting and creating more alcohol.  So add the sugar just before we filter all of the yeast particles, then you have sweetened and sterile wine that can no longer ferment because you’ve taken all of the yeast cells out of the wine.

If, however, all of the yeast was not removed during filtration or you haven’t sterilized the bottling equipment well enough you will get another round of fermentation only this time it will be in the bottle.  When this happens you get fizzy wine that will often pop the cork and get wine all over the place.  We’ve had this problem and it’s quite embarrassing.  We think we’ve resolved that problem but you are always one contamination event away from a new batch of wine that will have this happen.

So if you drink wine that is more sweet than dry, you will probably run into this every once in a while.  Don’t worry about it hurting you, if it tastes good you can still drink it.  It will just be a little less sweet and it will be carbonated.  In this era carbonated wines are actually selling pretty well but most people who buy regular table wine don’t want any surprises.

Until next time

J. Stoeger

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