Every four weeks we do what is called topping in the winery. Wine evaporates through the pores in the barrel, what we call topping loss or what others, particularly those that age spirits, refer to as the “angels’ share”. Now, we don’t begrudge the angels their share (it’s good to have happy angels) but we do try to minimize this loss by keeping the barrels in a high humidity environment (ideally 70%) as low humidity accelerates this loss. For those of us who do not have the luxury of a wine cave, which has a natural high humidity, there are humidifiers that micronize water droplets and spray them across the winery, slowly building up the humidity. However, after four weeks, enough wine has evaporated to create problems aside from the obvious one that if left to it’s own devices, you would have little wine left by the time it’s ready to bottle.
As part of our quality control measures, when we top the barrel (fill it to the brim) we also adjust the free sulfur dioxide (FSO2) levels- FSO2 acts as an anti-microbial and anti-oxidizing agent. When there is too much headspace (or ullage if you want a fancy wine term for it) or the FSO2 levels are off you have a much greater chance of bad things happening to your wine: you could get film yeast development, aldehyde increase-which is not good unless you are making a sherry, or an increase in volatile acidity (VA) which gives the wine the dreaded vinegar aroma. The entire process- sampling the wine, testing, adding FSO2 when needed and finally the topping- takes us an entire week. We just finished the topping for January last week- hopefully, the angels enjoyed their share and will send us some rain as a thank-you!