During the course of time – days, weeks, months, and years – that wine is aging in the barrel, evaporation occurs. As the wine evaporates, it creates headspace at the top of the barrel (ullage is the French term for this process). The wine barrels need to be kept full in order to keep oxidation from occurring in the wine, so winemakers spend time ‘topping off’ each of the barrels to keep wine levels at a maximum.
True or False: Exposure to oxygen is always bad for wine.
Wines that are exposed to excessive oxygen and become spoiled are said to be oxidized. Oxidation is a threat as soon as the grape is crushed, which is why high-quality grapes are transported to the winery as fast as possible. When a grape is crushed, oxygen immediately starts to react with the juice compounds. An obvious visual change is the browning of the juice (more apparent in white wines than reds). However, some winemakers deliberately encourage a certain amount of oxidation prior to fermentation, particularly with Chardonnay, in order to develop a greater range of flavors. Also, at the beginning of fermentation, some aeration is necessary since yeast needs oxygen for growth. Often times too, aeration prior to serving can be beneficial in helping bring out the aromas and flavors.
Originally published in The Gold Wine Club's Wine Press, Cloisonné Wines edition.