It might be surprising, but balsamic vinegar comes from white grapes. Some common grapes used are the Trebbiano, Sauvignon, Spergola, and Lambrusco.
Balsamic vinegar ("BV") originates from both Modena and Reggio Emilia in Italy. Both are protected by the Italian DOCG (Denominazione di Origine Protetta) and the EU Protected Designation of Origin.
According to the EU PDO, BV of Modena or Reggio Emilia must have the following characteristics:
In producing BV, a "mother" starter is added to get the fermentation going. This starter may have originated from strains of yeast and bacteria dating back to the origin of BV itself.
To make things more confusing, there are "matured" balsamics and "aged" balsamics. Matured versions have a minimum storage in wooden barrels of 2 months up to 3 years. Aged versions exceed 3 years. Some aged balsamics exceed 100 years in age, if not more. Their price tag reflects that too.
Matured BV's are best suited for salads while Aged BV's work best alone or as a main enhancer to fresh dishes. If using an aged in a salad it's best to use it alone.
BV is aged in multiple barrels of multiple types. This process of going from one type of wood to another over a period of years are some of the most closely held tradesecrets in the food business with master fermenters staying their entire lives with the distillery. Woods used include chestnut, cherry, ash, juniper, mulberry, walnut, acacia and oak. For a traditional BV to be tradizionale it must be aged in at least five of these woods.
As the aging process is performed, the size of the barrels shrink use in size since bout 10% of the fermentation is lost yearly due to evaporation.
Unlike wine, the aging of BV benefits from fluctuations in temperature. Many producers age their products in their buildings attics to get the full effect of seasonal temperature variations.
Traditional BV's were not available in the US until the mid 1970's due to import restrictions.