How exactly is wine made? You are probably aware that wine comes from grapes, but what makes it different from grape juice?

Chemistry and biology are what make wine unique and determine its flavour. With a more thorough understanding of the science behind the wine making process, the more likely you are to enjoy and appreciate wine.

Throughout history, many scientific discoveries have led to advancements in vinification (wine making), viticulture (the growing of grapes) and wine storage. Science is what gives wine its alcohol, taste, smell, and wine could not exist without it.

The Chemistry of Wine

The chemical processes that create wine and make it unique.

Wine is simply grape juice that has been allowed to ferment and undergo chemical changes. Wine can be made from fruit other than grapes, but these only account for about 1% of all wines produced. Without chemistry, wine could not be smelled, tasted, or even created.

We are able to smell wine only because when we inhale, its molecules travel through the air to the rear of the nose; a chemical reaction occurs, and the brain tells us what we are smelling.

Wine is created by a combination of chemical processes. The sun's warmth increases the sugar content in grapes, and this sugar provides a food source for the yeast. In the fermentation process the yeast convert the sugar into alcohol, which is followed by another chemical process, "malolactic fermentation". Lactic-acid bacteria in the wine produce enzymes that break down the malic acid into lactic acid and carbon dioxide. This second process is both discouraged and desired, depending on the region and the characteristics desired in the wine; excess fermentation can result in a dull wine with "off" odours.

The process of "fining" clarifies the wine by adding an element to the wine to absorb, move, or chemically react with sediment to remove it. The main element used today is a type of clay called bentonite.

The Biology of Wine

How does nature create wine? How do living yeast and bacteria affect wine?

Biology, the study of life, is important in understanding wine because wine is alive. Grapes are the fruit of living vines, and are themselves home to biological activity; wild yeast strains and the preferred wine-producing yeast, Saccharomyces cerevisiae, are found on the grape skins.

Grapes, and ultimately wine, are affected by living moulds, yeasts and bacteria. There are diseases that affect grapes and can kill the vine. For example, in 1863 Phylloxera (an American louse that kills grapevines) spread throughout Europe and destroyed many vineyards. Using biological methods European growers were able to preserve the European grapes by grafting them to American roots, which were immune to the bug.

The warmth of the sun increases the sugar content of the grapes as they grow on the vine. During fermentation, this sugar provides food for the yeast (still on the skins, along with bacteria). Sometimes additional yeast is added, and the type and amount, as well as the temperature during fermentation will affect the time required for maturation and the final flavour. Living micro organisms can ruin the wine and so the fermentation must be controlled; a common method is to add sulphur dioxide (in legally defined quantities).

After the yeasts convert the sugar into alcohol, lactic acid bacteria convert malic acid to lactic acid and carbon dioxide in a process called "malolactic fermentation". The bacteria lower the acidity and add flavour compounds, ultimately changing the flavour of the wine.

Yeasts and bacteria in the wine can continue to change its flavour as it ages (in wooden barrels, stainless steel tanks, and even in the bottle). It is the living element in wine that can improve or ruin a wine's flavour with age.