We do this periodically to prevent the wine from spoiling.
A barrel is not an airtight container such as a stainless-steel drum. A barrel will allow evaporation of wine through the wood itself and the tiny spaces between boards of the staves and the heads. This evaporative process drives the phenomenon called microoxygenation (or microx) that can soften tannins and add complexity to the wine. More on this in a later post! As the wine evaporates, it must be replaced to prevent spoilage. The increased airspace in the barrel (called ullage) leads to oxidation and the increased air – wine interface can harbor bacteria and spoilage yeasts. How often we have to replace the lost wine, referred to as “the Angel’s Share” depends on a few factors including the age of the barrel, the temperature and humidity of the cellar, air movement, the type and thickness of the oak (or other wood), and even the density of the wine. Water and alcohol are both lost, in proportions dependent on wine content, temperature and ambient humidity. And yes, the evaporative loss of wine must be reported to our government overseers so they can account for the loss of tax revenue!
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