Making red wine

Red Bordeaux wines are made from dark-skinned grapes with clear juice. In order to give them their color and tannins, the pigments contained in the skin have to be transferred to the must through maceration. From this maceration depends the tannic and aromatic framework of a red wine.

1. Stemming and crushing. 

Hand-harvested grapes are sent to a de-stemmer to separate the berries from the stems (the whole stalk system connecting the berries to the cane). After being sorted to remove unripe or damaged fruit, the berries are passed through a crusher where they are lightly crushed, not mashed, to release the juice. However, not all winemakers practice crushing: some prefer to send the uncrushed berries directly into the fermenting vats to respect the integrity of the grape. All the juice, skins and pips — or uncrushed berries — then go into the fermenting vat. In most cases, a little sulfur dioxide (SO2) is added in order to prevent both the oxidation of the grape’s flavors and the development of certain micro-organisms that may affect fermentation.

In recent years, at some wineries, alcoholic fermentation has been preceded by a phase of cold prefermentary maceration (sometimes called a cold soak) using dry ice to control the temperature. This operation aids the selective diffusion of certain compounds in the grape such as flavors and pigments.

 

2. Alcoholic maceration and fermentation (first fermentation)

The fermentation tank may be made of wood, stainless steel, or plain or coated concrete. It may have a variety of shapes: recently, the eggshaped concrete vat has become rather popular, while in general, wood and concrete have been enjoying a revival. Nowadays, most vats are internally or externally thermoregulated, which allows, among other things, temperature control during alcoholic fermentation.

 

Cold prefermentary maceration and alcoholic fermentation are carried out together on a monovarietal basis: one vat may only contain the juice of one grape variety and, preferably, of one single plot. At this point, blending has not happened yet. The must (grape juice) and skins (the whole skin mass is also known as pomace or marc) macerates for twenty-one days, sometimes longer, depending on the intended type of wine.

These phases of prefermentary and fermentary maceration allow the extraction of pigments and tannins from the skin to the juice. After a few days in the vat, the must begins to ferment under the natural action of grape yeasts. Alcoholic fermentation starts above 16 to 18 °C (60 to 64 °F) and may reach about 28 to 30 °C (82 to 86 °F; it may be controlled through thermoregulation as necessary), for an average duration of 18 days. Through that process, the sugars contained in the grapes are turned into alcohol while carbon dioxide and heat are also released.

During this stage, the pomace (the skin and pips) converges towards the top part of the vat into a mass that is called a “cap”. Specific techniques are used to facilitate the extraction of the grape components by immersing the cap and preventing the growth of harmful bacteria that are likely to proliferate in the solid parts emerging above the must; pumping-over consists of pumping the juice from the bottom to the top of the vat and pouring it over the cap. Delestage or “rack and return” consists of emptying all the juice from the vat by gravity, at the end of which the cap is pressed by its own weight when it settles at the bottom of the vat.

Then the juice poured out of the vat is poured back in from the top so that the cap is fully immersed. Pigeage, or punching-down, is a very old technique that inspired the two previously mentioned methods: using a pige (pestle) held at arm’s length through the opening of the vat (or using a mechanical pige), the winemaker breaks and immerses the cap. After the first fermentation, an extra postfermentary maceration may follow, also under temperature control, so that the wine’s tannins have a chance to build a complete structure.

3. Drawing off and pressing.

The fermented must is separated from the pomace (skin + pips) before being transferred into another vat. At this stage, it is known as free-run wine. Then the pomace is gently pressed to extract the remaining juice: this is called press wine. Pneumatic or hydraulic presses are used for this purpose.

During blending, the more tannic and deeply-colored press wine may be added in varying proportions to the free-run wine depending on the type of wine one wishes to obtain.

 

4. SECOND FERMENTATION.

Known as malolactic fermentation, this second fermentation takes place after alcoholic fermentation. It contributes to the successful evolution of the wine by reducing its acidity, due to bacteria that convert malic acid into lactic acid, also with a release of carbon dioxide. This second fermentation may be carried out either in vats or in barrels. As blending has not taken place yet, free-run wine and press wine can undergo their malo separately.

5. RACKING.

Once the two fermentations are complete, the wine is racked: it is separated from its lees (dead yeast cells), which settle in the bottom of the vat or barrel. During the racking, the wine is slightly sulfited, which helps to stabilize it, protecting it against oxidation and possible risks of alteration by some micro-organisms. At this stage, a range of separate wine vats is used.

6. Aging. 

Wine is a living product. During the aging stage, it is clarified and matures after undergoing many internal biochemical transformations.

The aging of red wine is done in vats and/ or in oak barrels, for an average duration of twelve to eighteen months in Bordeaux. During this period, depending on changes in atmospheric pressure and temperature, the wine expands or condenses: this causes air pockets — which are potential sources of wine spoilage — to form at the top of the containers. To prevent this, one must ensure that the containers are always full to the brim by frequently pouring in a little extra wine — this is called topping-up or ullage. During winter, the wine is clarifyed by natural settling, then it is fined with egg white, which attracts any particles remaining in suspension in the wine.

Finally, throughout aging, between 2 and 4 rackings are necessary, with or without aeration, to promote the maturation of the wine and eliminate excess lees by adding oxygen in small amounts. 

 
 

When these operations are done, the wine is ready for the final blending.

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