It often appears at the bung stave for a simple reason: It is the weakest and most exposed to impacts. It is also one of the widest staves of the barrel.
During the bending process (the action of arching the stave by heating it to give it its curve), the wider the stave, the greater the mechanical stress will be.
Light heating (referred to as toasting in this case, aromatic toasting) releases and softens the tensions in the fibers of the wood less than strong toasting. Therefore, they are more likely to cause cracks.
When the barrel is shaped, it remains under constant tension because the wood seeks to return to its original form. The steel hoops help maintain its shape.
Drilling the bung stave creates an additional weakness. The tensions in the wood fibers, initially concentrated in the center of the stave, are now distributed on either side of the bung hole, in a section of wood that has become much weaker. The stave becomes more fragile, allowing surface cracks to appear over time.
To maintain the integrity of the liquids, cracks that do not exceed half the thickness of the stave can be tolerated.
However, to avoid worsening the situation, the insertion of the bung must be done carefully on cracked staves.
Depending on the type of bungs used, the risk of cracks appearing or worsening is higher or lower.
Traditional wooden bungs are generally accompanied by a fabric square placed between the bung and the bung hole to form a seal. They are driven in with a mallet to create the seal. The risk of worsening is real if the bungs are hammered in too forcefully.
Silicone bungs, which are softer, are compressible and create a better seal than wooden bungs. They are usually inserted by hand, but some wineries still hammer them in to ensure the seal. The risk of worsening is low, even if the bungs are driven in forcefully.
Lastly, expandable bungs which allow for the bung’s volume to increase once inside the bung hole using a screw system. The sealing process is gentler and without impacts, significantly reducing wear. The risk of worsening is negligible.
Handling, such as “rolling on the bilge” can also cause stave breakages, especially when the barrel strikes the bung holes during the process.
This is just one example among many potential incidents that can occur in a barrel’s life. Other signs of wear, such as oxidation of the hoops or wine stains, are influenced by other factors.
It is important to keep in mind that these small defects are purely aesthetic. The external appearance remains important but it is not the main factor in determining the price of a barrel.
Let’s remember that proper handling and appropriate use will extend the integrity of your barrels and wines and spirits.