How Wine Is Made
Winemaking begins in the vineyard. Without ripe grapes, there is not much a winemaker can do to create a fine bottle of wine. The next step is to get the juice out of the grapes under controlled conditions. These days, that will not involve the use of feet, but the use of sanitary equipment.
Once the juice has been exposed, the winemaker can allow the natural yeast clinging to the grape skins to turn the sugars in the juice into alcohol and carbon dioxide, or she can neutralize the native yeast and add her own strain. The process of converting sugars into alcohol and carbon dioxide with the aid of yeast is called fermentation.
When nature is in balance, all goes according to plan. The reality, of course, is that nature can be annoyingly unpredictable, and a winemaker can run into a plethora of problems in the quest to produce an outstanding bottle of wine. Fortunately, technology has come to the aid of winemakers in an activity that is a careful balance of art and science.
There are many technological options available to the modern winemaker. But — whether the end product is red, white, or pink, or whether it's cheap or expensive — there are several principles common to all winemaking.
Harvesting and Preparing the Grapes
In order to make the best wine possible, the grapes must be picked at just the right moment of ripeness. As grapes ripen, their sugar content increases. At the same time, their acidity declines. The trick is to harvest them when the sugar and acid levels are in balance. This is always a subjective judgment by the winemaker and is based on what style of wine he is producing.
During harvest it is crucial that the grape skins not be split open prematurely. The winemaker does not want fermentation to begin before the grapes enter the winery. While handpicking is the most gentle, mechanical harvesting machines can handle grape bunches with some care. Handpicking, incidentally, is more expensive for a winery than mechanical picking.
Inside the winery, crushing the grapes produces a combination of juice, skins, and seeds called the must. If red wine is the goal, the must will go into a tank for fermentation. If white wine is the goal, the seeds and skins will be separated from the juice as soon as possible, and only the juice will go into the tank or barrel for fermentation.
Fermenting the Juice
Winemakers can “manage” fermentation to enhance the resulting wine. Fermentation usually takes place in large stainless steel tanks, but winemakers can choose to ferment in large oak tanks to add complexity and to refine the wine's texture or mouthfeel. Many white wines are fermented in smaller, sixty-gallon oak barrels to add richness and a toasty character.
In addition to alcohol and carbon dioxide, fermentation generates heat, and high temperatures kill yeast cells. Therefore, fermentation tanks usually have sensors installed that alert winemakers if temperatures approach the danger zone. At the flip of a switch, winemakers can activate cooling systems also installed in the tanks to bring the temperatures down to a more safe level.
Grape skins rise to the top of the fermenting must, forming a “cap” over the juice. This cap needs to be broken up and mixed back in to extract the desirable qualities from the skins. The cap is pumped or manually punched back with a paddle. Manual punching can release more tannin from the skin and add to a wine's structure or backbone.
Winemakers also have options when it comes to yeast. Instead of relying solely on naturally occurring yeasts, they can add cultured yeasts to the juice that are better suited to the kind of wine they're producing. Natural yeasts often produce off-aromas and flavors in wine, so cultured yeasts can yield more predictable results. Some yeasts strains have better alcohol tolerances, and still other strains can help add a flowery perfume to white wines.
When fermentation has ended, the winemaker does not always remove the wine from the tank or barrel immediately. For many red wines, the winemaker will leave the new wine in contact with its skins for several more days or even weeks. This allows more color to be extracted from the skins and gives the wine time to soften. This process is called maceration. White wines fermented in small oak barrels will often stay in contact with the lees — dead yeast cells and bits of grape matter left over from fermentation — for several days for the sake of a fuller, richer texture.
Aging the Wine
After fermentation, some wines are ready for immediate bottling. Rosés, many whites, and light reds are bottled soon after fermentation and should be drunk while still young. Others will be aged — either in stainless steel or oak — for several months or up to several years.
Fine red wines, in particular, need to age in oak to reach their full potential. This aging often takes place in sixty-gallon barrels and allows the wines to soften and absorb some of the wood's flavors and tannins. Winemakers must be careful, however: Too much time in oak overpowers the wine with the wood flavor and astringency. Additional aging can take place in the bottle.
When the wine moves from fermentation tank to barrel, it is cloudy because of the dead yeast and tiny particulate matter, or lees. Over time, the lees settle at the bottom of the barrel. At this point the winemaker can begin clarifying the wine. Using special equipment, the clearer wine can be pulled or “racked” off the lees and the barrel flushed out. The wine is then returned to the barrel to continue its aging. Racking is frequently done more than once before the wine moves to bottle.
Some winemakers think that fining and filtering remove too much flavor and body from the wine, and forego those processes. The resultant wines (sometimes labeled “unfined” and “unfiltered”) may have a small amount of sediment in the bottle, but the winemakers believe a fuller flavor will more than offset any inconvenience to the consumer.
As the wine gets closer to bottling, the wine can be clarified on a more microscopic level using a process called fining. When fining agents — such as charcoal, bentonite clay, casein (milk protein), or egg whites — are added to the wine, they grab onto the solid particles and drag them, over a period of days, to the bottom of the tank. The wine can then be separated from the sediment and fining agents by racking. Some winemakers will further clarify the wine right before bottling by filtering it through layers of paper filters or synthetic fiber mesh.
Sometimes during aging, a winemaker will add special bacteria to encourage a process called malolactic or secondary fermentation (ML or MLF, for short). This process converts the sharper malic acid in the wine into the softer lactic acid. In terms of what you sense in your mouth, imagine a Granny Smith apple at one end of the spectrum and milk at the other. Most reds and some whites undergo ML.
If a white or red wine is a blend, this combining of several grape varieties in distinct proportions often happens during aging. For example, many Cabernet Sauvignon wines contain dashes of Merlot, which can add a softer, fruitier note to the Cabernet's muscular tannins.
Bottling the Wine
When a wine is ready for release, it's bottled in a highly mechanized process that keeps the wine from contact with the air, germs, and impurities. Many wineries have elaborate bottling lines that fill, cork, cap, and label spotless wine bottles with little human intervention. For the finest wines it is often advantageous for the winery to keep the bottles in storage for two or more years. This makes for better wine when it finally reaches the market and, in many cases, substantially increases its value.