In red wine, grapes are harvested, crushed, and fermented with the skins in a tank or vat. The contact with the skins distinguishes the production of red wine from white wine. The skins provide colour, flavour and tannins, and the yeast added in the fermentation process will transform the sugar into alcohol.
Harvest
The harvest runs when the grapes reach their optimum point of ripeness, which usually occurs from the end of Summer to the beginning of autumn. The harvest is made by hand or mechanically, with a machine which shakes the vines making the berries fall onto a conveyor belt that transports them to a deposit. As the grapes arrive at the winery may go through a sorting process to remove unwanted berries, leaves and other debris.
Destemming and crushing
At this stage, the winemaker decides whether to destem the bunches (remove the stems) or ferment the whole grape bunches. This is an important decision, as the stalk is rich in certain compounds that, when in excess, may give the wine an unpleasant bitter and astringent flavour. This astringency is due to the tannins present in the stalk, skins and seeds. Destemming also reduces the wine's acidity, so this is an important decision due impact on the wine's profile. At this stage, sulphur dioxide is add to prevent grape oxidation and deterioration by undesirable bacteria. Crushing corresponds to the compression of the skins and, as the name indicates, the crushing of the pulp without damaging the seeds, creating the so-called must. Must, is the combination of grape skin, juice and seeds before fermentation. In the past, crushing was done by foot treading. Although some smaller producers still use this traditional method, nowadays, destemming and crushing are done by a de-stemmer/crusher.
Fermentation and alcoholic maceration
At this stage, some winemakers decide to cool the must for a few days in a process called "cold soaking" to extract the colour, aroma, flavour and tannins from the grape skins in a balanced way without creating alcohol. Fermentation then begins. At this point, the winemaker can also opt for a prolonged maceration that occurs in parallel with fermentation. In this case, he has less control over it but improves the wine's structure and tannins.
Fermentation is a biochemical process that transforms the must's sugars into ethanol through the action of yeasts. It may be spontaneous or induced.
Spontaneous fermentation, also called natural or wild fermentation, occurs naturally through indigenous yeast action. Indigenous yeasts are found in the grapes and the winery's atmosphere, converting the must's sugars into alcohol and carbon dioxide.
Induced fermentation occurs from commercial yeasts added to the must. The use of commercial yeasts allows the winemaker to produce consistent wines year after year. Indigenous yeasts are more challenging but often produce wines with purer and more complex aromas.
During fermentation, the solid part of the must, skins and pips, is pushed to the surface due to the release of carbon dioxide that forms the so-called "cap". This cap has to be submerged several times in a manual process or using specific equipment.
Fermentation is the most critical and complex process in wine production. In this phase, temperature control is of the utmost importance. When the must is fermenting, it absorbs oxygen and releases carbon dioxide and heat. If the temperature is not controlled it can reach such high values that it can kill the yeast. Nowadays, there are very sophisticated refrigeration systems to control the temperature. Most of this process is made in temperature-controlled stainless-steel tanks.
Malolactic Fermentation
Also called second fermentation, this may or may not occur. Almost all red wines have malolactic fermentation. In this stage, a small army of lactic bacteria transforms malic acid into lactic acid and reduces the total acidity. Malolactic fermentation gives balance, smoothness and aromatic complexity. Usually, it is done after alcoholic fermentation.
Pressing
In the case of red wine, pressing occurs towards the end of fermentation. Pressed wine is more astringent due to higher phenolic compounds, which may cause unwanted bitterness. Therefore, the most crucial decision the winemaker has to make at this stage is what pressure to apply when pressing the masses.
Racking
After fermentation, solid residues settled at the bottom of the tank. At this stage, the wine is transferred to a clean tank. The purpose is to separate the clear wine from the lees at the bottom of the tank so that they do not impart an unpleasant taste to the wine and to be preserved in the best sanitary and organoleptic conditions. This process is called racking. Racking is also a form of natural clarification of wine and could be complemented by a provoked clarification to remove substances that were not eliminated in this process.
Ageing
Wine can age in several containers: wooden barrels, stainless steel tanks, concrete tanks, amphorae or bottles. Each of these containers will affect the wine's flavour in different ways and, as the time it stays in ageing.
Wooden barrels allow for more oxygenation, soften the tannins and acidity, and give different aromas and flavours to the wine as vanilla, buttery and spicy notes.
Stainless steel tanks, where there isn't exposed to oxygen, give wines a fresher character and preserve more of the primary aromas.
Concrete tanks allow micro-oxygenation and provide aromatic complexity without the wine acquiring the aromas and flavours of wooden barrels.
Amphorae, or clay amphoras, also provide micro-oxygenation and give the wines minerality, freshness, a characteristic earthy texture, and aromatic complexity from the inner lining that takes pine resin, beeswax and aromatic herbs, and which is used in the more traditional amphora wines.
Bottle ageing changes the wine's texture and provides a complexity of aromas and flavours of its own.
Not all wines are made for ageing, so this is another step carefully planned by the winemaker.
Clarification
At the end of the ageing period, the wine needs to be cleaned to be bottled. There is a technique called fining, in which clarifying agents such as gelatine, egg white or casein are added to the wine to remove impurities that were suspended in the wine and not eliminated by racking. Besides fines, there are other techniques to clarify wine: centrifugation, filtration and flotation.
Stabilisation
This process allows the wine's colour and clarity to remain stable over time and indifferent to the conservation limits regarding temperature, light exposure and aeration. There are three stabilisations to perform: heat stabilisation, cold stabilisation and microbiological stabilisation.
Heat stabilisation prevents the wine from becoming cloudy when submitted to high temperatures.
Cold stabilisation inhibits the formation of crystals when submitted to low temperatures.
Microbiological stabilisation prevents the wine from fermenting again in the bottle.
We should mention some winemakers choose not to clarify and stabilise their wines because they believe it affects their texture, flavour and aroma. There is quite a bit of debate on this point.
Assemblage
Assemblage or blending is the mixture of two or more wines from different grape varieties. This phase may occur in different stages. It may be placed after fermentation or after ageing.
Bottling
Bottling is the last stage of this complex and very long process. In this phase, a final adjustment of sulphur dioxide called sulphites is made. The bottles have to have the least possible exposure to oxygen. Nowadays, this is a much easier process than in other times as technology minimises the risks of oxidation and contamination that could occ
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