Ever wonder how balsamic vinegar gets made? The "good stuff" is from Modena, Italy, and is aged in barrels 25 years. These barrels are graduated from a larger one at the top of the photo to smaller ones. As the vinegar ages and gets "thicker" it goes into the smaller barrels. Each barrel is a different type of wood. And the vinegar in each barrel tastes entirely different.
If you thought barrel tasting was only for wine...think again. This stuff is heavenly...right from the barrel.