WHAT IS FERMENTATION IN WINE?

Here is a breakdown of how it works:

     After the grapes are crushed, the resulting juice (and sometimes skins, seeds, and stems) is called must. This mixture contains natural sugars—mainly glucose and fructose.

     Yeast (either naturally occurring on the grape skins or added by the winemaker) consumes these sugars. During fermentation, it produces:

 - Ethanol (alcohol) – gives wine its intoxicating quality

 - Carbon dioxide (CO₂) – escapes as bubbles

 - Heat – which can affect the fermentation speed and wine flavor

White wines: typically ferment at cooler temperatures (50–60°F / 10–16°C) for several weeks to preserve delicate aromas.

Red wines: ferment warmer (75–85°F / 24–30°C) for 5–10 days to extract color, tannins, and flavor from the skins.

     When most of the sugar is consumed, the yeast becomes inactive and settles as lees (sediment). The winemaker may stop fermentation early to retain some natural sweetness or allow it to complete for a dry wine.

     Fermentation also produces subtle flavor compounds called esters and phenolics, which contribute to a wine’s aroma, texture, and complexity.