Updated: Jun 9
Wine is fermented grape juice but its type and style depend on how it is made. Types of wine distinguish winemaking processes, resulting in still, sparkling, or fortified wine. Styles of wine are differentiated by organoleptic properties, such as color or taste. The winemaker and appellation regulations determine the style of each type of wine.
This post will focus on how most wines are commercially made today. However, it should be noted that "natural wines", i.e., those made from grapes with nothing added or removed, eschew many of these steps as they are considered more akin to "manufacturing" wine.
You're more likely to make better wine if you start with better grapes so in many ways viticulture is the first step of winemaking. However, this article will focus on winemaking beginning with the harvest. The timing of the harvest is affected by grape variety, weather, style of wine to be made, physiological measurements, and appellation regulations.
Grapes are harvested by hand or by machine. A manual harvest may be by cluster or by berry, Clusters allow the winemaker more options when making wine. Making several passes through the vineyard, picking berry by berry, allows wines to be made from grapes with specific traits like botrytised berries. A machine harvest is more economical but slaps the berries off the vines rather roughly, though I'd expect the technology to improve. Once harvested, handling of the grapes matters. If you put the grapes in a large container, gravity will break the skins of the berries at the bottom, exposing the released juice to oxidation. Sparing use of sulfur dioxide or a blanket of heavier than oxygen inert gas, picking when cool, and rapid transportation to the winery are the main tools to keep the grapes fresh.
After harvest the grapes are delivered to the winery and may be destemmed and sorted to remove stems, leaves, dirt, insects, critters, and diseased or sub-par grapes. Agrochemical residue, animal urine, and other MOG that cannot be removed by sorting, presumably do not survive the rest of the winemaking process as winemakers don't wash their grapes.
White, orange, pink and red still wines are made with many similar steps but in an order suitable for obtaining the desired style. White wines separate the juice from the solids before fermentation while other styles ferment first. Blue wine is an organic beverage with no denomination of origin, produced by one company; it may be generous to call it wine. Constructed wines and spirits (e.g., Replica Wine and Endless West) may or may not be regulated under the U.S. Department of the Treasury Alcohol and Tobacco Tax and Trade Bureau (TTB) or the U.S. Department of Justice Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) but I will not discuss them here.
Despite similar color, orange and pink wines taste different because of how they are made.
Orange wine is made from white grapes using the process normally used for making red wine, namely by fermenting the juice with their skins for several days or longer, and often with minimal additives. Appellations producing orange wine classify them as white wine. Pink wine is made from black grapes, fermenting the juice with their skins for a few hours.
When making white wines the grapes are crushed immediately after harvest. Crushing means the grapes are ripped open, releasing the free-run juice. If harvested by cluster the grapes are usually destemmed. Sulfur dioxide is added at this stage to prevent premature fermentation, oxidation, and spoilage, and it helps to break down sticky pectin. Sulfur dioxide passes through the cell membrane of microbes and renders them harmless by changing the properties of its proteins and enzymes. Aromatic grapes may benefit from skin contact ("maceration pelliculaire") with the free run juice at low temperatures or by leaving the grapes in a cool place overnight before crushing. To minimize extraction of harsh polyphenols, the free-run juice should be drained without disturbing the skins.
The crushed grapes are then pressed to extract the remaining juice. Pressing means releasing the remaining juice by rupturing the tougher cells near the skin under pressure.
The winemaker chooses how much of the generally inferior press juice to include in the blend depending on the style and vintage conditions. Most white wines are effectively press wine as the harvested grapes are usually pressed, not crushed, after destemming.
After pressing, the remaining solids, referred to as pomace, are disposed of or distilled into a pomace brandy known by many names including Marc (France), Grappa (Italy), Orujo (Spain), Tresterbrand (Germany), and Raki (Greece).
The juice, referred to as must, is then chilled and left to settle ("débourbage") for about a day so the larger particles can fall to the bottom of the vat. Depending on appellation regulations, acid or sugar may be added before fermentation to adjust the acidity and alcohol in the final wine.
After clarification by settling, alcoholic fermentation is started. Temperature during fermentation of white wines is usually maintained between 59-68°F (15-20°), depending on the grape variety and wine style being produced. Temperature control during fermentation is important because if the temperature is too cool a pineapple aroma dominates and if the temperature is too warm the wine becomes dull.
Primary, or alcoholic fermentation, means yeasts, a single-celled fungi, convert the sugar in the must into ethanol and carbon dioxide. Fermentation may be started using wild yeasts (non-saccharomyces) or by adding cultured yeast (usually saccharomyces cerevisiae or saccharomyces bayanus) from companies like Lesaffre/Redstar and Lallemand. Yeasts proliferate with oxygen but must be switched to anaerobic mode after fermentation starts or water rather than alcohol would be produced. Fermentation in wood barrels achieves the greatest complexity though stainless steel tanks are often used for fresher styles.
If most of the sugar is converted into alcohol, the wine is referred to as "dry". The winemaker may also decide to leave residual sugar in a wine so it tastes "off-dry" or "sweet" by filtering out the yeast or by adding neutral grape spirit which kills the yeast.
Secondary, or malolactic fermentation (MLF), also known as malolactic conversion (MLC), means lactic acid producing bacteria (LAB) convert the malic acid in wine into lactic acid and carbon dioxide. Oenococcus, lactobacilllus, and pediococcus are the main types of LAB. MLF reduces acidity and increases complexity by generating diacetyl, the source of a buttery character. MLF also increases stability by consuming bacterial nuturients. However, MLF also reduces some fruity esters so is typically not used to make many white wines other than Chardonnay. Many sweet styles of white wine do not use MLF because they ferment grape juice that has been concentrated by noble rot, freezing, or drying, and has little malic acid to soften.
To clarify the wine it is then transferred ("racked") into another container to remove the dead yeast and particulates, referred to as "gross lees", which can impart a bitter taste.
After fermentation, the wine may rest on its lees ("sur lie") for many months to impart greater complexity, flavor, and usually a "toasty" quality to the wine. Lees are the yeast (mostly dead) and particles of grape skin and cells that lie at the bottom of the barrel at the end of fermentation. As the yeast decomposes it creates a reductive environment which may result in hydrogen sulphide being produced. To avoid this rotten egg smell, oxygen must be introduced by stirring the lees ("batonnage") or by rotating the barrels.
The winemaker controls the style of the finished wine by blending at this point. Blending means mixing wines that have been made using different methods, or from grapes grown at different places, or from different grape varieties. Blending should occur before further clarification or stabilization treatments because it can render the wine unstable again.
The wine may then be stabilized, meaning that the wine is processed to keep it clear after bottling at both high and low temperatures. Fining wine heat stabilizes it by removing tannins and unstable proteins which cause haze. Fining agents, which have a negative charge are attracted to the unstable proteins in wine that have a positive charge and form a precipitate that can be removed by settling or filtration. Albumin (in ox blood and egg whites), gelatin (animal-, fish-, or vegetable-derived), and casein (in milk) proteins can be used as fining agents but some may wish to avoid use of animal based products, even if not a component of the final wine. In this case, bentonite (a clay formed from volcanic ash) and for white wines only, silicon dioxide (in silica sol), PVPP (a plastic), or activated charcoal may be used as fining agents. Cold stabilization follows, meaning tartaric acid is either precipitated out of the wine or its crystallization is prevented. Stabilization should not have a noticeably negative effect on the quality of a wine if properly carried out but low intervention winemaking may be the best approach.
After several months, and several rackings, the remaining particulates, referred to as "fine lees" will have settled out. If the winemaker isn't satisfied with the speed or clarity achieved by racking, a centrifuge (flushed with nitrogen to prevent oxidation) or filtering may be employed, though these methods may remove desirable flavors.
At this point white wines will be bottled, corked/capped, labelled, and packed. Some white wines, particularly those from France, Germany, and Spain will benefit from bottle age.
When making red wines, before the crusher-destemmer was introduced, grapes were fermented without destemming. This is still commonly practiced in Bourgogne (Burgundy). If uncrushed, some of the sugar in the grape berries will be converted into ethanol via enzymes rather than yeast in a process known as carbonic maceration, commonly used in Beaujolais. Stems, sometimes roasted, may also be added to absorb sugars and acids in the must and serve as channels for the liquid to run.
At this point the grapes are crushed and sulfur dioxide is added to protect the must. Although it sounds rougher than pressing, crushing simply breaks the berry skins, releasing the free-run juice. The key point is that the juice and the skins are fermented together because the skin, not the juice, imparts color to most red, pink, and orange wines.
The must (juice and skins) may undergo a cold soak before fermentation to extract fruit aromas without tannin. Alcoholic fermentation runs about 5°F warmer than for white wines, and lasts for up to 3 weeks. Color and tannin can be extracted from the skins by several methods that keep the skins mixed with the juice. The gentlest method, known as "punch down" ("pigeage"), pushes the skins that have floated to the top of the vat back into the must. A less labor-intensive method known as "pump over" ("remontage"), sprays juice pumped from the bottom of the vat over the top and results in a greater level of extraction. The "rack and return" method (délestage), empties the fermenting must into another tank and then returns it to the original vat where the skins remain at the bottom. This process is the fastest and most thorough of the three. The alcohol in the must extracts the pigment and tannin from the skins. Varying the timing and frequency of punch down, pump over, or rack and return allows winemakers to control how much extraction takes place.
Primary fermentation may be followed by maceration. Maceration means soaking the must to extract phenolics (tannins, color, flavors) from the skins, seeds, and stems into the juice. The free-run wine ("vin de goutte") is drained into a tank or barrel and the remaining must is put in a press to yield a more robust press wine ("vin de presse"). After pressing the remaining solids are either disposed of or distilled. The wine is then racked into another container to remove the gross lees, followed by secondary fermentation. While MLC is often skipped when making white or pink wine it is usual when making red wine.
Barrel maturation at this point allows the wine to acquire flavors from the barrel, soften its tannins, deepen its color, increase the complexity of its flavors, and slowly stabilize and clarify. Blending may occur before or after ageing in the barrel ("elevage").
Red wines are then stabilized, clarified, and bottled, corked, and labelled as with white wines. Finer red wines, as with some fine white wines, also benefit from bottle ageing.
When making pink wines winemakers may or may not have a choice as to the production method, depending on regulations and tradition. The "bleeding" method ("rosé de saignée"), also called short maceration (rosé de macération), begins as for making red wine but drains out some pink juice after macerating less than a day, and then proceeds as for making white wine. The remaining juice is used to make a more robust red wine. Making two wines from the same grapes allows the pink wine to be sold earlier than the red wine which may benefit from ageing. The "direct press" method is used to make delicate pink wine and is essentially the same as for making red wine but the juice remains in contact with the skins only a few hours. Blending red and white wines together to make pink wine ("rosé d'assemblage") is not common except for sparkling wine. Rarely, pink wines may be made by removing some color from red wines using charcoal, presumably because the lighter color boosts sales.
A few examples of appellations that make pink wine using each method may be useful.
Direct Press: Provence, though the winemaker may choose to use the bleeding method
Blending:: Champagne, though some producers (e.g., Francis Boulard & Fille) use the bleeding method. Some new world winemakers, such as some from New York and New Jersey, also blend red and white wines to make pink wine.
Sparkling wine production begins with making still wine. Top quality sparkling wines and white wines made from black grapes are often harvested by hand and pressed without destemming.
There are several methods used to make sparkling wine which all entail dissolving carbon dioxide in the wine. Most methods also involve removing the lees remaining after fermentation because the lees makes the wine cloudy. As you might suspect, the main determinant of the quality of a sparkling wine is the quality of the wines it is made from. However, since the still wines used to make sparkling wines (called base wines) are somewhat bland and quite acidic, balance is key to making more than a carbonated wine.
Both pink and sparkling winemakers believe it is more challenging to make their wine than red wine. While pink wine producers have to balance color with tannin extraction I suspect it is more challenging to make good sparkling wine because minor faults in the base wine are accentuated by the presence of bubbles and because blending ("assemblage") is more art than science. While some champagnes like Jacquesson and some grower champagnes promote vintage or terroir differences like fine still wines, most focus on producing a consistent house style, year after year. They do this by blending "reserve wines" from previous vintages (at least 15% of each harvest in Champagne is reserved for future blends) with typically 80% of the base wines from the current vintage.
Sparkling wine is usually made using the traditional, transfer, or tank methods. Each method starts by blending base wines (and optionally reserve wines) as a "cuvee" and adding sugar and yeast (referred to as liqueur de tirage). There are also variations on these methods which will be discussed below.
Second fermentation, not to be confused with secondary fermentation described above, means inducing another alcoholic fermentation and trapping the resulting carbon dioxide in the wine rather than releasing it in the air. This produces the bubbles in sparkling wine.