Because the aging process of wine is one in which chemical and enzymatic reactions act to diminish various flavor components in the wine, the amount of liquid contained in a wine bottle can have an effect on the process.
For instance, the more liquid present in a larger format bottle (1.5L) means that it will take longer for the various reactions to influence the wine’s taste. Therefore, larger format bottles age more slowly than standard format (750ml) or even smaller format (500/375ml) bottles.
Bottle fill is important because the fill, or ullage (the distance between the bottom of the cork and the top of the liquid level in the bottle) of the bottle is an indicator of the amount of oxygen present in the bottle, which in turn will greatly influence the aging of the wine. Less fill, or more ullage means that more oxygen is present within the bottle.
Oxygen poses the greatest threat to properly aged wine, since too much oxygen can greatly accelerate the aging process. Too much ullage, marked when the fill of the bottle is below the midpoint of the shoulder of bottle (the shoulder is the upper curved portion of the bottle just beneath the neck of the bottle) is also a sign that the bottle has probably seen dramatic and rapid temperature changes during its storage, which can also act to prematurely age, or even spoil fine wine.