During ageing some wine is lost because of evaporation. If the room is very humid the alcohol content of the wine will actually go down while if the room is very dry the alcohol content will go up slightly.
To prevent the staves in the barrels from drying out we therefore have to top barrels once a month. This is quite a big task if you have 800 barrels and we use quite a bit of wine in the process. This is also the main time when the wine gets some air contrary to most peoples belief that air comes in through the staves.
So our main aim today is to top and replace the bit of wine comonly referd to as the angels share.