top of page

How Fermentation Turns Grape Juice Into Wine

1:34 · October 13, 2026 · Wine

Lesson 1 of The Science of Wine. Yeast turns the sugar in grape juice into alcohol, and that one reaction explains why a wine tastes dry or sweet and why some wines feel fuller than others. The lesson ends on the fruity versus sweet mix-up that trips up a lot of customers.

Go deeper

In this video

  1. 0:00 Lesson 1: Fermentation
  2. 0:08 Yeast turns sugar into alcohol
  3. 0:18 Riper grapes, more sugar
  4. 0:30 Dry vs. sweet
  5. 0:43 Alcohol adds body
  6. 0:52 Where you taste it
  7. 1:08 Fruity vs. sweet
  8. 1:16 Three things to remember

Transcript

Lesson one. Fermentation. This is the reaction that turns grape juice into wine.

Yeast eats the sugar in grape juice and turns it into alcohol and carbon dioxide. That one reaction is what separates wine from grape juice.

It starts in the vineyard. Riper grapes hold more sugar, and more sugar means more potential alcohol. That's why warm regions tend to make fuller, higher-alcohol wines.

A wine is dry when the yeast finishes the job and almost no sugar is left. A wine is sweet when some sugar stays behind, usually because the winemaker stopped fermentation early.

Alcohol also adds body. Higher-alcohol wines feel fuller and warmer. Lower-alcohol wines feel lighter.

So where do you taste it? Sweetness is the first thing you notice in a sip. Alcohol shows up as weight in your mouth and warmth on the finish. Check the label. A 14.5 percent Zinfandel will feel richer than a 12 percent Pinot Grigio.

One trap to watch for: fruity versus sweet. A dry wine can smell like ripe peaches or berries and still have no sugar in it.

So remember three things. Yeast turns sugar into alcohol. Dry means the sugar is gone. And alcohol is your clue to body. Next, put it to work.

More videos

bottom of page