How Wine Is Made: From Grape to Glass

Picking time is a style decision: writing about rosé, WSET lists it alongside the vineyard site, the grape varieties and the production method as decisions that each affect the style of the final product. Oregon State University Extension names pH, titratable acidity (TA) and Brix as the standard grape compositional measurements, and notes that Brix values are typically used to estimate the potential alcohol of the finished wine. Climate sets the pace. Jonathan Pedley MW, writing for Decanter, explains that in a cool country like Germany the grapes ripen slowly and keep high levels of acidity, while a hot climate usually gives wines with more alcohol and soft acidity. Grapes are picked by hand or by machine. Hand picking is labour intensive and costly but allows the grapes to be sorted carefully at the vineyard or winery. Machine picking is quicker and cheaper but does not allow the same rigorous sorting, and in hot climates it allows harvesting in the cool of night. However the grapes are picked, they need to reach the winery as quickly as possible.

• Oregon State University Extension names pH, titratable acidity and Brix as the standard grape compositional measurements.
• Cool climates keep more acidity in the grapes; hot climates usually give more alcohol and softer acidity (Decanter).
• Hand picking allows careful sorting but is labour intensive and costly; machine picking is quicker and cheaper but less selective (Decanter).
• In hot climates, machine picking allows harvesting in the cool of night (Decanter).

Hand-picked grapes can be sorted carefully at the vineyard or at the winery. The next step is de-stalking, which removes the stalks from the grapes. Pedley notes that the stalk contains woody tannins; some winemakers still include the stalks in their fermentations to extract them, but the more normal practice is to de-stalk the grapes when they arrive at the winery. The grapes are then crushed open to break the skins and release the sugary, colourless juice, which is also called must. Grape pips contain bitter oils, so whatever is done in winemaking, it is important to avoid crushing them (Decanter). At this point, the paths for red and white wine diverge. For white wine, the skins are typically removed straight away by pressing, in which a machine separates the skins and seeds from the juice. For red wine, the grapes are not pressed until after fermentation: skins and juice ferment together (WSET).

• Stalks contain woody tannins; de-stalking on arrival at the winery is now the more normal practice, though some winemakers still ferment with stalks (Decanter).
• Crushing breaks the skins to release the sugary, colourless juice (WSET).
• Grape pips contain bitter oils, so winemakers avoid crushing them (Decanter).
• White wine grapes are pressed before fermentation; red wine grapes are pressed after it (WSET).

Yeast, a single-celled fungus, consumes the sugars in grape juice and converts them into ethanol (alcohol) and carbon dioxide. The AWRI names Saccharomyces cerevisiae as the yeast most commonly responsible for alcoholic fermentation in winemaking, and Decanter notes it is also known as brewer's yeast because it is used to make beer and leaven bread. During fermentation, yeasts also produce small amounts of volatile compounds, such as esters, aldehydes and sulphur, which can contribute to the aroma and flavour of the finished wine (Decanter). Winemakers choose between ambient or 'wild' yeasts naturally present in vineyards and wineries and strains cultivated for winemaking needs. Some winemakers consider indigenous yeasts part of the local terroir, but Decanter notes that they carry the risk of unwanted strains such as Brettanomyces, and that wild Saccharomyces yeasts can be ineffective and unpredictable; to ensure a smoother, more controlled fermentation, many modern wineries use pre-selected strains. Temperature matters. Pedley writes that most white wines ferment between 15 and 20 degrees to retain freshness, taking about two weeks for all the sugar to be converted into a dry white wine, while most reds ferment relatively warm, at 25 to 32 degrees, to assist colour extraction. The AWRI warns that temperatures above 35°C can begin to affect yeast health and increase the risk of a stuck fermentation. Fermentation does not always run to dryness: WSET defines residual sugar as the unfermented sugar left once fermentation has come to an end or has been deliberately halted by the winemaker, and notes that most wines are dry, usually with 2 to 3 grams per litre.

• Yeast converts grape sugar into ethanol and carbon dioxide; Saccharomyces cerevisiae is the yeast most commonly responsible (AWRI).
• Some winemakers see wild yeasts as part of terroir; pre-selected strains give a smoother, more controlled fermentation (Decanter).
• Most white wines ferment at 15 to 20 degrees; most reds at 25 to 32 degrees (Decanter).
• Halting fermentation leaves residual sugar; most wines are dry, usually with 2 to 3 g/L (WSET).

WSET notes that the appearance of any newly made wine is determined almost exclusively by contact with the grape skins. WSET explains that the colour of wine comes from the skin of the grape while the juice itself is colourless, so red wine must be made from black-skinned grapes whose skins stay in contact with the juice. During red fermentation, colour is extracted from the skins along with tannin, the compound responsible for the grippy, mouth-drying sensation of red wine, and temperature and time both play a role in how deeply coloured and tannic the wine becomes (WSET). The colour compounds are anthocyanins, located in the skins of black grapes (Decanter), and the AWRI notes that maximum extraction of colour occurs before that of tannins. Once a cap of skins has formed on the ferment, winemakers manage it, for example by punching it down with a tool or by pumping the liquid from the bottom of the tank over the top; the AWRI lists plunging, pump-overs and rack and returns as the traditional cap management options. The AWRI describes plunging with a stainless steel or plastic plate on a pole, generally one to three and up to five times a day, and pump-overs that draw must from the bottom valve of the fermenter and discharge it over the top of the cap, typically two to three times a day. The AWRI considers pump-over extraction gentler than plunging, and notes that plunging is more likely to be used with lighter-coloured varieties such as Pinot Noir. After fermentation, most red wine drains off by gravity as free-run wine; the skins and pips are then pressed to release press wine, which can be harsh and tannic but is sometimes blended with the free-run wine to improve its body (Decanter). White winemaking works the other way: the crushed grapes are pressed straight away and the clear, sugary juice is fermented into white wine (WSET). Rosé sits between the two. WSET describes short maceration, where crushed black grapes spend a short period on their skins before pressing; direct pressing, where the juice is taken off the skins quickly and fermented like a white wine; and blending red wine with white wine.

• Wine colour comes from the grape skins; the juice is colourless (WSET).
• Red fermentation extracts colour (anthocyanins) and tannin from the skins (WSET, Decanter).
• The AWRI considers pump-overs gentler than plunging; plunging is more likely with lighter-coloured varieties such as Pinot Noir.
• Rosé is made by short maceration, direct pressing, or blending red wine with white wine (WSET).

Once alcoholic fermentation has finished, the wine can undergo a second transformation called malolactic fermentation, or MLF. The AWRI defines it as the conversion of malic acid to lactic acid and carbon dioxide, carried out by some of the lactic acid bacteria, and names Oenococcus oeni as the bacterium most often responsible. Decanter notes that MLF softens acidity by converting harsh-tasting malic acid into softer lactic acid, raises the pH of the wine, and is technically a bacterial conversion rather than a fermentation because it does not use yeast. The bacteria like to operate in a warm environment, which Decanter gives as +16 degrees Celsius, so traditionally winemakers had to wait until the spring after harvest; modern cellars and tanks can be heated to start MLF as soon as desired. Most reds undergo MLF, although reds grown in very warm climates that lack natural acidity do not benefit from it. Among whites, MLF is generally undesirable in aromatic, high-acid styles such as Riesling and Sauvignon Blanc, while Chardonnay and Viognier routinely go through it (Decanter). Winemakers can inhibit MLF by adding SO2 after fermentation or by using enzymes such as lysozyme. MLF also helps stabilise a wine by preventing a spontaneous MLF later, potentially after bottling.

• MLF converts malic acid to lactic acid and carbon dioxide, carried out by lactic acid bacteria, most often Oenococcus oeni (AWRI).
• Most reds undergo MLF; reds from very warm climates that lack natural acidity do not benefit from it (Decanter).
• MLF is generally undesirable in aromatic, high-acid whites such as Riesling and Sauvignon Blanc; Chardonnay and Viognier routinely go through it (Decanter).
• Winemakers can inhibit MLF with SO2 after fermentation or with enzymes such as lysozyme (Decanter).

Once fermentation is complete, the winemaker decides where and how long to age the wine. Pedley writes that most white wines are matured for a short period, usually around six months, while red wine is usually matured longer, around 18 months or more. WSET notes that oak is now a winemaker's choice rather than a necessity, used to give distinctive aromas and flavours. Heating the staves during coopering toasts the inside of the barrel, and the wine gradually takes on those flavours; the most common are baking spices such as vanilla, cinnamon and clove, and the more time a wine spends in barrel, the more oak flavour it takes on (WSET). In red winemaking, Decanter describes oak barrels as central to élevage, where the key is the wine's relationship with oxygen: exposure to just the right amount promotes reactions that intensify colour and soften hard tannins. Size sets the strength of the effect. The Bordeaux barrique holds 225 litres and a Burgundy barrel usually 228 litres; the smaller the barrel, the higher the proportion of oak in contact with the wine and the stronger the oak-derived aromas and flavours. Larger barrels, typically 500 litres and above, reduce the barrel influence and age the wine more slowly (Decanter). Wine matured in stainless steel retains its pure fruit character (Decanter), and Decanter describes steel tanks as airtight. Concrete tanks are commonly used in wineries; the egg-shaped concrete vessel, designed by Michel Chapoutier with Nomblot, gives a continuous flow to the wine as it ferments and ages, and its thick walls keep the temperature very stable during fermentation (Decanter). Clay came before both: WSET notes that long before stainless steel tanks and oak barrels, wine was fermented in buried clay vessels, and Decanter notes that Georgia's winemaking culture has 8,000 years of documented history and that Georgians have fermented and aged their wines in clay qvevri since antiquity. WSET explains that, like oak, fired clay permits limited oxygen exchange but, unlike oak, contributes virtually no wood-derived aromas or flavours.

• Toasted oak barrels give baking-spice flavours such as vanilla, cinnamon and clove; more time in barrel means more oak flavour (WSET).
• The Bordeaux barrique holds 225 litres; smaller barrels give stronger oak-derived aromas and flavours (Decanter).
• Wine matured in stainless steel retains its pure fruit character (Decanter).
• Fired clay permits limited oxygen exchange but contributes virtually no wood-derived aromas or flavours (WSET).

Before bottling, the wine is clarified and stabilised. The AWRI explains that a fining agent is added to soften or reduce astringency or bitterness, remove proteins capable of forming haze, or reduce colour; the agent reacts with wine components to form a new complex that can separate from the wine. The fining agent causes the lees to fall to the bottom, from where they can be racked off (Decanter). Common fining agents include gelatine, isinglass, egg whites, casein, bentonite and carbon (Decanter). Bentonite is a very fine clay formed from volcanic ash, used principally to remove proteins from white wine and juice. Egg whites remove phenolic compounds associated with harsh astringency in red wines; as a guide, the AWRI puts the number of egg whites added to 225 litres of wine at 2 to 8. Casein, the principal protein in milk, is used mainly for fining white wine and Sherries. The AWRI advises fining only when necessary and at lower rather than higher rates, because it can remove positive flavour characteristics. Filtration is a separate step, used to remove any remaining yeast or bacteria from a wine. Pedley describes three main filter types: kieselguhr (diatomaceous earth) as a first stage, cellulose pads that remove most remaining yeast, and membrane filters that remove all remaining yeast or bacteria. Some winemakers prefer not to fine their wines, and many natural wine producers do not fine or filter (Decanter). Sulfur dioxide concentrations are set at bottling. Decanter describes SO2 as a preservative added to nearly all wines to protect them from oxidation and microbial infection, and the AWRI has traced sensory deterioration, premature oxidation, microbial spoilage and high volatile acidity in submitted wines to insufficient SO2 at bottling as a major contributing factor. The last step is the closure. Natural cork is a tried and tested material but can spoil a wine through cork taint or by allowing air into the bottle; synthetic corks are on the rise, and some advocate screw tops for day-to-day wines (Decanter).

• Fining agents react with wine components to form complexes that separate from the wine (AWRI).
• The AWRI's guide is 2 to 8 egg whites per 225 litres of wine.
• Membrane (sterile) filters remove all remaining yeast or bacteria (Decanter).
• The AWRI traces premature oxidation and microbial spoilage in some wines to insufficient SO2 at bottling as a major contributing factor.

Primary sources (the Australian Wine Research Institute, WSET, and Oregon State University Extension): https://www.awri.com.au/industry_support/winemaking_resources/frequently_asked_questions/fining_agents/, https://www.awri.com.au/wp-content/uploads/2023/05/s2350.pdf, https://www.awri.com.au/industry_support/winemaking_resources/winemaking-practices/fermentation-temperature/, https://www.awri.com.au/industry_support/winemaking_resources/fining-stabilities/microbiological/avoidance/sulfur_dioxide/, https://www.awri.com.au/industry_support/winemaking_resources/fining-stabilities/microbiological/glossary/, https://www.wsetglobal.com/knowledge-centre/blog/2021/september/23/what-determines-the-colour-of-wine, https://www.wsetglobal.com/knowledge-centre/blog/2021/december/14/what-is-wine, https://www.wsetglobal.com/knowledge-centre/blog/2023/november/29/types-of-ros%C3%A9-from-around-the-world, https://www.wsetglobal.com/knowledge-centre/blog/2021/july/27/why-is-oak-used-in-winemaking, https://www.wsetglobal.com/knowledge-centre/blog/2026/qvevri-the-ancient-vessel-at-the-heart-of-georgian-winemaking, https://extension.oregonstate.edu/catalog/em-9583-preparing-harvest-grape-chemistry-prefermentation-adjustments. Secondary: https://www.decanter.com/learn/winemaking-the-facts-2-54064/4/, https://www.decanter.com/learn/winemaking-the-facts-2-54064/6/, https://www.decanter.com/learn/winemaking-the-facts-2-54064/7/, https://www.decanter.com/learn/winemaking-the-facts-2-54064/8/, https://www.decanter.com/learn/what-is-malolactic-fermentation-51591/, https://www.decanter.com/learn/wine-yeast-45474/, https://www.decanter.com/learn/advice/what-is-fining-51651/, https://www.decanter.com/learn/sulphur-dioxide-so2-45859/, https://www.decanter.com/learn/concrete-eggs-winery-ask-decanter-316358/, https://www.decanter.com/premium/amphora-wines-joy-of-clay-421186/, https://www.decanter.com/learn/barrels-explained-477859/, https://www.decanter.com/learn/wine-barrel-sizes-explained-464044/, https://www.decanter.com/learn/oak-barrels-335990/. Last verified 2026-09-28