Elevage and Air
Elevage, Oxidation & Reduction, Oxidative Aging vs. Reductive Aging, Barrel-Aging, Micro-Oxygenation & Racking

Elevage is a French term that covers the process of developing, raising, or “educating” the wine in the cellar before bottling. Negociants in Burgundy frequently refer to themselves as “eleveurs” as they maynot be the winemaker but do perform the elevage. Cellar temperature, types of tanks and/or barrels, the kind and age of the barrels used, the frequency and type of racking, setting the bottling date and a host of other things all are part of elevage. Much of the process of elevage boils down to managing the effect of air, and more specifically of oxygen, on the developing wine. If little or no “air effect” or oxidation is desired, the wine is either bottled very young or kept in tanks to age before bottling. If some oxidation is desired (as for many great whites and almost all great reds), the wine is put into barrels for a period of aging before the final blending (or assemblage) and bottling. The barrel-aging process encourages a “controlled oxidation” as a small amount of wine (called the angels’ share) evaporates out and air works in through the staves. A warmer, drier cellar promotes more evaporation and development while a colder, damper (more humid) cellar discourages evaporation. Therefore, wines from cooler cellars often taste less developed or younger. Racking – moving the wine by pump, siphon, or gravity from one barrel to another – exposes the wine to more air than barrel-aging alone.

Oxidation and reduction, while both “redox” reactions, are actually opposite processes. Technically speaking, oxidation is the process of a compound picking up an oxygen atom and reduction is the process by which a compound loses an oxygen atom. When talking about wine, the two terms are used to refer both to characteristics in a wine and to problems the winemaker must handle. Some aromas in wines may be described as “oxidized” (i.e. the smell of Madeira) or “reduced” (i.e. the smell of old eggs).

As a practical matter, certain grape varieties may be described as being “oxidative in nature” or “reductive in nature”. Because Syrah is “reductive in nature” (meaning it tends to develop reduced aromas), it needs to be racked (or in some other way exposed to air) periodically to give it the air it needs to develop properly in the barrel. Because Pinot Noir is “oxidative” (meaning it has a tendency to oxidize), it can develop oxidized (even “Madeirized”) aromas and drop color if it is over-exposed to air so care must be taken to minimize manipulation, rackings, and evaporation.

When describing the aging processes used for Port, bottle-aged Ports (such as Vintage Port) are said to be “aged reductively” or with no external air contact or air exchange through the bottle or the cork while barrel-aged Ports (such as Colheita) are said to be “aged oxidatively” or in contact with air over a number of years in the cask and are subject to a controlled oxidation as the wine evaporates through the wood of the casks and air enters to replace it. Bottle-Aged Ports (reductive aging) retain their color and fresh fruit flavors while developing slowly; Barrel-Aged Ports (oxidative aging) lose red color and gain an “oxidized flavor” and dried fruit character while developing along a much different path.

While a wine is in barrels, it slowly goes through a series of chemical changes. Many wines undergo malo-lactic fermentation (a bacterial conversion of the wines malic acid to lactic acid) in barrels. While in the barrel, the wine slowly oxidizes and its poly-phenols gradually polymerize (form into larger and larger molecular chains) giving it a softer feel. During this time, the wine also clarifies as it drops a deposit called its “lees” in the barrel. Some winemakers want to get the wine off these lees and so they rack the wine into a clean barrel. Some will leave the wine un-racked and on the lees. Some wine makers want both the lees contact and some additional air for the wine so they may use a technique called micro-oxygenation whereby a small amount of air is bubbled into the wine using a device similar to a fish tank aerator. Winemakers working with Merlot and Syrah seem more inclined to using micro oxygenation.

These are the opportunities for oxidation during the cellaring or elevage. If managed properly with careful elevage, oxidation at this level is all good as it allows the wine to develop and gets rid of any reductive character the wine might have before bottling. Careless elevage can lead to either reduced flavors in the bottles wine or more likely, to a wine that tastes tired and dried out when it should be in its prime.

When oxygen combines with compounds in wine, those compounds can pick up one or more oxygen atoms and become “oxidized”. These new compounds have different sensory characteristics. For example, when ethanol (the main alcohol found in wine) is oxidized it becomes acetaldehyde – which in turn can be oxidized to form acetic acid. Each smells different.
Similarly, polyphenols (tannins, anthocyans, and flavonoids) can be oxidized to quinones, and metals such as copper, iron, and manganese can be transformed from Cu+ to Cu2+, Fe2+ to Fe3+, and Mn2+ to Mn3+, respectively.
Reduction is the opposite of oxidation; it is a process whereby compounds lose oxygen atoms. Sense wine fermention is an anaerobic process (without oxygen), a number of “reduced” compounds are produced. Reduced sulfur and nitrogen compound such as hydrogen sulfide and mercaptans, are well-known for the negative “reduced” or reductive” characteristics they give to wines.

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