Tim Hubbard, co-founder of Markko Vineyard, testing a sample of wine from a barrel in the winery’s cellar.

The device shown on top of the barrel is a fermentation lock attached to a bung. Still used in wine production, the lock allows carbon dioxide to escape during fermentation without letting air in and the bung, a stopper, provides an airtight seal. Air exposure for any significant period of time will cause wine spoilage.