Wine is not all one thing. Winemaking processes different from grape to grape, from region to region, from high-end to low-end, certainly from style to style. To break down this complicated subject at least a little bit, we will cover winemaking by dividing it into five general areas:
- Red wines
- White wines
- Rosé wines
- Sparkling wines
- Fortified wines
Red Wine Making
The process of making red wine begins with the harvest. Since the skins of red wine grapes contribute to the wine’s color and flavor, the careful harvester tries to keep the bunches of grape whole. Individual plastic boxes are used to avoid a situation in which grape skins will break from the weight of grapes above (if the grapes were, for example, shoveled into a large hopper). The careful winemaker will put together a sorting line, so that quality grapes can be separated from shriveled or diseased grapes and also to avoid getting any matter other than grapes (MOG) into the fermentation vessel. The grapes may then be sent through a de-stemming machine or be de-stemmed by hand. Some red winemakers choose not to de-stem, and send the stems into the fermentation vessel with the grapes. The stems can add tannins.
The next step is to crush the grapes. This was traditionally done with an implement that seemed perfectly designed for crushing grapes without crushing the seeds inside: the human foot. Crushed seeds can add bitterness to the mix. Modern crushing machines now use rollers or paddles to do the same thing. Some are combination crusher-de-stemmers.
The crushed grapes and the juice they exude next go into a fermentation vessel. The winemaker at this point will either add commercial yeast or depend on local ambient yeast
to begin the fermentation process. During fermentation, yeast converts the grape sugars into alcohol. This alcohol acts on the skins of the grapes to extract anthocyanin pigments, flavor elements, and phenolic compounds, particularly tannins. The seeds also contribute tannins. This alcoholic extraction is generally not enough to produce a deep colored red wine, however. The wine requires an additional soaking, or maceration period, to bring out all its potential color and flavor. A low-end, mass-produced red wine might see a fermentation period of only several days. A big red wine designed to age might undergo a fermentation of a week followed by an extended maceration of several weeks. In order to extract color, red wine is usually fermented at a higher temperature than white wine. In addition, exposure to oxygen is more prevalent in red winemaking than in white. This is because phenolic compounds in red grape skins, stems and seeds slowly react with the oxygen to form pigmented tannins, which contribute positively to the red wine’s eventual texture.
The crushed skins, seeds and stems, if any, in red wine fermentation tend to float to the top of the fermentation vessel and form a “cap” that tends to prevent contact between the skins and the juice. Two methods come into play to integrate the cap materials with the juice in order to assure maximum extraction. In punching down (pigeage in French), a winery worker will use a spade-like tool to break the cap and push it down to the bottom of the fermenter, allowing the juice to rise to the top. This procedure, still done primarily by hand, must be done several times a day over the fermentation and maceration period. In pumping over, a hose is placed deep into the fermenter to allow wine from the bottom of the fermenter to be pumped over and onto the top of the cap, thus breaking the cap and circulating its contents among the wine. This is often accomplished using automatic devices.
After the wine goes through its alcoholic fermentation it might undergo an additional pressing operation. The free-run wine from the initial crushing is collected in a tank. The skins and seeds that remain are then sent through a wine press, creating what is known as press wine. The free run wine is often of a better quality than the press wine. Since the majority of the grape’s acidity is lodged in the grape pulp, free run juice is more acidic, press wine more tannic (the tannins come from the skins). The two types of wine may be processed into separate batches of wine, or they might be combined. With a traditional basket press, the winemaker turns a large screw device that serves to press the grapes so that the press wine runs out at the bottom. Modern wine presses, which are often computer controlled, can exert a specified amount of pressure on the grapes, and have the ability to generate multiple press runs of different pressure levels. This is a way to arrive at just the right level of tannin in the press wine so that the combined wine has the balance of tannin and acidity the winemaker is looking for. At this point (or further down the line during the barrel aging process), the red wine might be racked: pumped from one container to another so that sediment may be removed in successive stages.
Most red wine undergoes a process of malolactic fermentation at some point after the primary fermentation is completed. In “malo,” lactic acid bacteria (which may already be present in the wine or may be added) metabolize harsh tasting malic acid in the wine and replace it with softer lactic acid. This operation must be carefully monitored because it tends to reduce the total acidity in the wine. Acidity, especially in warm climate regions, is a precious commodity.
Not all red wine sees contact with oak, but in general red wine is matured in oak barrels or casks much more frequently than is white. In barrel maturation, substance like phenolic tannins already in the wine combines with phenolic compounds from the wood for additional level of flavors. As with any process in winemaking, oak contact must be accomplished with skill and some restraint. Serious red wines age eighteen months or longer. The winemaker must choose between new oak, oak used one or more times, and among types of oak (French or American, for example) before determining the final blend. The size of the barrel also makes as a difference—the smaller the barrel, the greater the oak contact. In less expensive wines, oak chips, staves, and even oak juice are often used to add oak elements more quickly. In some parts of Europe, woods other than oak, like acacia or chestnut, are sometimes used.
Before blending and final bottling, wines may go through a process called fining. The winemaker adds a fining agent to the wine that attracts and clumps up fine particles, yeast cells (alive and dead), and tannins the winemaker wishes to remove from the wine. The now-heavier particles sink to the bottom where they can be racked out. Many fining agents are based on animal products: blood and bone marrow, casein (milk protein), chitin (fiber from crustacean shells), egg albumen (derived from egg whites), fish oil, gelatin (protein from boiling animal parts), isinglass (gelatin from fish bladder membranes), diatomaceous earth (remains of ancient sea creatures). To make a wine vegan, non-animal alternatives are bentonite clay, kaolin clay, plant casein, silica gel, vegetable plaques, and limestone (although as to the last, it seems to this writer than a strict vegan would take limestone off the list, since, although it is a rock, it is derived from the remains of ancient sea creatures).
Nearly all wines get doses of sulfur dioxide to act as an anti-microbial agent and antioxidant to prevent spoilage. Filtering, which is controversial because many believed it detracts from flavor and liveliness in a wine, can remove some microbes, but only preservatives like sulfites can keep the microorganisms down over the long term. The alternative, in a sulfite free wine, is the keep the wine refrigerated at all times from bottling to consumption (and, even so, it should not be kept for long before enjoying). For a wine to keep long term, it needs chemical protection.
In fine wines, the various phenolic and other compounds continue to interact and gain layers of sophistication when aged in their bottles. At least this is the potential, but so much depends on how the wine is shipped and stored, and the intangibles of organic chemistry.