🍷 Bung

Bung is the stopper that closes the hole in a barrel, made of wood or silicone. A bung (barrel bung, cask bung) is the stopper in the bunghole of an oak barrel, through which the barrel is filled, topped up and sampled. The hole is one of the ways air gets into a barrel, along with the gaps between staves and the wood itself.

A barrel slowly loses wine. A new one soaks up 5 to 6 litres. So Australian advice is to top it up two weeks after filling, then every couple of months (2 to 3). In the cellar, humidity of 65 to 75 percent is best, as drier air speeds evaporation.

You do not need to chase every drop, though. In a properly bunged barrel a partial vacuum builds up over time, and topping too often breaks it, which may speed oxidation. How often to top is a matter for the winery's HACCP plan, based on the wine's chemistry, its lees and how clean the barrels are. Headspace over the wine, on the other hand, is a risk: microbes grow at the wine and air boundary and volatile acidity rises.

Mould, vinegar flies and red stains tend to gather around the bunghole, from wine spilled while topping or sampling. Scrub them with a brush and a 1:1 mix of SO2 and citric acid, and keep chlorine away. An empty barrel that has been stored dry is closed with a silicone bung once sulphur gas is inside.

The bung shuts the barrel and the hoop holds its shape. Together with topping up, they shape how wine ageing goes in an oak barrel.