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It is my first grape wine home brewing and I have been reading up a lot regarding yeast fermentation. I like my wine bit sweet and I read that either adding alcohol as in port method or adding a preservative once wine gets completely dry then back sweetening are two ways people do it. My doubt is, can adding more sugar get me the same result?

More sugar means more alcohol and yeast cant ferment beyond a limit so thereby having residual sugar sweetens the wine. However I read about stuck fermentation that happens when sugar content is more so how is it different from arresting fermentation like in port if ultimately I need is an off dry or sweet wine?

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There are a few ways to sweeten wine: Filtering, Mutage, too much sugar and adding something sweet after the wine has finished. Commercial wineries do not use sorbates to kill the yeast and preserve some of the sweetness. It screws up the flavor.

By far the most used way to preserve sweetness is to filter a wine either before it's done fermenting or add sugar and then sterile filter. Sterile filtering in this case is .3u (micron). This is also done in conjunction with a pretty high dose of potassium bisulfite to keep the little bugs from refermenting again.

Mutage is a french term for adding alcohol to a still fermenting wine (think Port or Madeira) and can make wonderfully sweetish wines that last for hundreds of years. I tasted a Madeira from 1780 a couple of years ago. It blew my mind. No filtering necessary here since above 20% alcohol it kills the yeast.

You can keep adding sugar until you reach the theoretical limit of the yeast, but you will have problems with this as the yeast will keep trying to ferment slowly over many years and you are likely to end up with bottle grenades randomly exploding over time. Since you can't get it over 20% naturally, there is a space between around 17% and 20% where the yeast is kind of still alive trying to ferment.

You could also suppress the yeast with a really high dose of potassium bisulfite, but then that also gives off flavors.

I think you have to choices. Either bring the alcohol level above 20% with vodka (you will have to figure out the math on that) or just add a bit of sugar to your bottle before you want to consume it. Without investing in a sterile filter, this is all you really have.

  • I have found many sources online that mention alcohol tolerance of yeast is also an important factor. So my doubt is, would adding more sugar to a low alcohol tolerance yeast (as in Bakers yeast) during fermentation inhibit the process so as to leave out residual sugar? or would yeast still be alive? – rahul rj Nov 19 '17 at 8:33
  • Yes and no. Yeast is highly variable and not uniform. It quickly adapts to it's environment. Suppose you did what you wanted to do, but a tiny fraction of the yeast like the higher alcohol environment, then they would survive and continue fermenting. It's a crap shoot. Keeping residual sugar in wine is one of the hardest things about winemaking. There is a product you might try, but you need to ferment in a very control environment scottlab.com/product-97.aspx It's called PRODESSERT Double encapsulated yeast for premium dessert wine fermentation – farmersteve Nov 19 '17 at 15:11
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Another option is to add non fermentable sugar (sweetener like Glycerin). Wine making stores will often sell it in bottles labeled as "Wine Conditioner".

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Adding sugar beyond the point of a yeast ability to ferment it is the common way to make a sweet wine. Sometimes the sugar has to be added in two or more stages to fit the fermentaion characteristics of the yeast. Too high a concentration of sugar can stifle yeast as much as alcohol can. If the yeast has attenuated fully then sugar can be added to sweeten the wine without a yeast metabolic inhibitor (which I tend to shy from recommending anyway). However sweet wine must be of sufficient ABV to inhibit bacteria as well. If it isn't then one might have a reason to use a preservative (eg sorbate).

It might be supposed that the flavour profile of sweet wines will be different according to how the final ABV was achieved. The last stages of natural fermentation of a high gravity juice may produce differing flavour profiles compared to the inhibited fermentation of a subsequently fortified wine.

Within those provisos and IMHO, adding alcohol to a wine is effectively the same as the yeast producing and reaching its own alcoholic limit.

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