- Grow Grapes
- Harvest Grapes (Later Harvest = Sweeter Grapes)
- Use Yeast to Ferment Sugar into Alcohol
That’s it. The final step is interesting though, because the yeast is picky. If there’s too much sugar, heat or alcohol, it’ll quit. So, the winemaker has control over the yeast’s effectiveness. In the “efficient” varietals, the yeast ferments through all nearly all of the sugar, so that value is quite low ( .5 – 5 grams / Liter). There are plenty of exceptions.
In port, fermentation is halted by brandy, so there’s lots of alcohol and lots of residual sugar. In sweeter champagnes, sugar is added-post fermentation. And in dessert sauvignon blancs, which are being pushed by Napa wineries lately, the grapes stay on the vine super-late and end up with a high sugar content. The fermentation process is halted somewhat prematurely by altering temperature and a sweet, moderately alcoholic wine is the result.