“Oxygen is the enemy”…Or so I’ve been told over and over again by the pioneers in extreme reductive wine making. This attitude about oxygen is the reason for stainless steel ferments and storage, and often touted as a motivator for screwcap closures. However, I find it a bit extreme. After all, these same wine makers are now delving into the world of micro-oxygenation—tiny bubbles of O2 forced into these air tight stainless steel tanks. These wine makers also fight reduction—the formation of hydrogen sulfite in an oxygen free environment—with copper sulfate, a heavy metal I have yet to put into my wines. I dislike reduction in wine almost as much a I despise Brett! (BTW, reduction smells like cooked corn and baby poop).
Yet, I agree that poor management of oxygen in contact with the surface of wine is a certain path to poor winemaking.
Oxidation shows itself in many ways in a wine, usually as a flaw. Exposure to oxygen in a bottle, due to improper storage after decorking it, reveals a walnut or cooked fruit aroma and flavor. Gassing or vacuum pumps can protect your wine. However, most flaws due to oxidation are produced in the winery.
Poor ullage management, or head space management, is the primary culprit in oxidized wines. Ullage is the empty space above the wine surface and the internal surface of the container. If that space is not filled with something, obviously oxygen fills that space, wreaking all kinds of havoc! Thus, wine makers are at constant battle with evaporation in cellars (The “angel’s share” of a barrel), topping off barrels and maintaining appropriate levels of SO2 to mitigate oxidation.
If left unchecked, the head space in a barrel can quickly spawn a surface yeast bloom, producing all kinds of flaws in the form of volatile aromas. Acetic acid (vinegar) Ethyl acetate (nail polish remover), acetaldehyde (bruised apple) are the most common results of poor headspace management.
A sure sign of an oxidized white wine is a brown coloration. The color components in a wine are extremely reactive with oxygen and will rapidly oxidize to form a brown or straw like color in whites, and an orange-ish tint in rosés.
We use gas to fill the ullage in containers that cannot be filled to the top with wine. I use argon gas to displace oxygen in red wines, and CO2 in whites. Argon is inert in an aqueous solution (like wine!) and simply lays on the surface of the wine like a protective blanket. CO2 is quite dissolve-able in wine, especially cold wine, and can protect wine on the surface as well as add a wee bit of tingle in a white that contributes to freshness. Some wine makers use nitrogen to protect wine, while I use it to sparge out bound oxygen with a bubbling stone in small quantities.