The wooden barrel was created around 300 BCE. To understand why brewers, vintners, and distillers use barrels; you have to look back to the Celts, those northern Europeans who lived around the Alps or what is current France and Germany before conquest by the Roman Empire. Northern Europe had timber in abundance and as these people began to trade, they needed reliable vessels for the transportation and storage vessels. Of course, you can easily make wooden boxes but then the problem becomes how to move them. A barrel, on the other hand can be rolled (either on its side or around its base, making it possible to store and move large amounts of products (not just beer and wine) easily. Early barrels were not charred and were reused many times for both foodstuffs and other cargo.
The idea of aging spirits, wine and beer in barrels is a 19th century innovation. Since barrels were used repeatedly, it was not uncommon for them to take on the taste and smell of their previous contents. This is not a problem if you want to store beer in a barrel formerly used for bourbon but might be if the last contents of your barrel were fish. Charring a barrel was a common way to clean and sterilize a previously used barrel. To remove the taste of pickles or fish, the barrel was burnt and scraped.
Since whiskey distilled in frontier America was often stored used barrels and shipped long distances, whiskey from Pennsylvania and Kentucky would spend months or years travelling down the Mississippi. Charred barrels were often sent to this less prestigious “export” market so these barrels might spend even longer in transit all the while taking on the color and cleaning properties of the barrel.
The charred wood acts as a filter, changing or eliminating various congeners in the distillate. Congeners are substances produced during fermentation, other than ethanol, that give whiskey much of its taste and aroma. By the time the whiskey reached its destination, it had spent a good deal of time in contact with the charred wood and had a superior flavor. It became apparent that the whiskey from charred barrels were preferable to that in uncharred barrels, and the longer in the barrel the better.
So, when you see my second hand charred barrels full of beer, don’t ask what was in the barrel before but rather how long the beer has been in that barrel. The longer, the better.