Managing Oxygen During Winemaking
Inert Gase Use in the Winery
The winemaking process is a dynamic one: from crush, to fermentation, on to post-fermentation cellar procedures, aging, and bottling. Each step along the way allows for the potential ingress of oxygen, whether wanted or not. While oxygen is considered by many to be the enemy of wine, this is not always the case. In fact, proper use of enological oxygen at crucial steps in the winemaking process is paramount to wine development. That said, many winemakers dutifully aim to eliminate it from the process altogether particularly in partial tank headspace. Proper gassing regimens and selection of the correct gas for a particular application is something that many do not do well and fail to fully understand the principals at play. The inert gases used by winemakers are usually nitrogen, carbon dioxide, and argon.
Argon is a heavy molecular weight gas that serves as a thick cover for blanketing wines in all areas of wine production. Argon is not soluble in wine and does not present the issue of dissolving, and therefore provides a longer-term blanket protecting the wine. One advantage is that its density is close to that of carbon dioxide, so it is more efficient at purging the air from a vessel than nitrogen.
Nitrogen is a gas that often used in wine production. As an inert gas, it will not dissolve in the wine and produce different or off-flavors. Nitrogen is also considered an inexpensive gas. The most common use of nitrogen is for transferring wine where pressurization is required (e.g., Bulldog Pup), for sparging to displace oxygen before bottling, and for bottle purging.
Carbon dioxide is also a common inert gas used at wineries. Because its molecular weight is heavier, it creates a greater blanket when introduced into a container�s head space. The outcome of a heavy blanket results in less chances for oxygen to enter and spoil wine. With more blanket coverage and inexpensive price, it is a popular choice to purchase for the best return. However, because carbon dioxide is soluble in wine, it will lose that protective blanket over a couple of weeks. The colder the wine, the more carbon dioxide dissolves.
Uses of Inert Gases
One of the most significant functions winemakers perform is managing the availability of oxygen to wine. Excessive oxygen exposure manifests itself first by reducing fruity aromas. From there, the negative effects of oxygen exposure in the wine are demonstrated by nutty aromas and an unattractive color. Oxygen also provides growth potential for a host of spoilage microorganisms, such as film yeast and Acetobacter, producing negative aromas and flavors. Inert gases are used to supplant air in places where air could come into contact with wine. There are three ways in which the inert gases are used: (1) sparging, (2) flushing, and (3) blanketing.
Sparging is the process of injecting fine bubbles of gas into the wine to remove dissolved oxygen. Wines are sparged with gas either via a gas line connection to a valve at the bottom of a tank, via a submersible bubbler, in-line during a wine transfer between tanks, or during pump-around of a tank. When the bubbles are dispersed, a partial pressure develops between the inert gas and the dissolved gas. The difference in partial pressure causes the dissolved oxygen to leave the wine.
Inert gas flushing takes place when the housing pumps and hoses which are used to move the wine between vessels are flushed with an inert gas, flushing out oxygen which could potentially come into contact with the wine and cause oxidation. The vessel which will receive the wine will usually also be subject to inert gas flushing for the same purpose.
It is important to take into account the amounts of oxygen a wine can pick up from the headspace when a container is not completely topped and its headspace is not purged with inert gas. This oxygen uptake is a diffusion process controlled by temperature and the wine surface area. Cold temperatures increase oxygen solubility in wine, while the reverse is true for warm temperatures. The larger the surface area the greater the amounts of gas exchange, resulting in more oxygen dissolving into the wine.
Click on the following topics for more information on managing oxygen during winemaking.