It all starts with the grapes. Yes, balsamic vinegar is made out of GRAPES! The grapes are grown in Modena, and are picked by hand.
The grapes are crushed and cooked down to create grape must, which is poured into a large barrel, which lies next to other barrels called a battery. Each barrel in the battery gets smaller and smaller in size.
Modena is very hot in the summers. One-fifth of the product evaporates, concentrating the grape must, and leaving all of the barrels in the battery partially empty.
Once a year, the barrels are made full again. We start at the smallest barrel, and take out a certain amount to bottle. We then fill it up (to make up for bottling and evaporation) using the contents of the second-smallest barrel. Now the second-smallest is missing an amount due to evaporation and the amount moved to the smallest barrel, and it made whole again using the contents of the third-smallest. And the third-smallest is made full using the fourth-smallest barrel. This process of moving the vinegar takes places one time per year.
In this way, this product has been in barrels for at least 6 years, and moved through 6 different barrels. It has developed a sweet and sour flavor, taken on flavors from the wood and the unique bacteria culture in each barrel. It has thickened into a dark and viscous liquid. The acidity has mellowed and the flavor lingers on your tongue, like a nice wine.
About the Barrels
Each barrel has its own combination of bacteria which, when combined with the flavors from the wood, gives the vinegar its characteristic flavor. The bacteria converts the sugars into acetic acid; proper bacteria cultures are needed, timing is important and the fermentation is controlled by a Mastro Acetaio (master balsamic vinegar maker). Unlike wine barrels, which become less valuable each year, an Acetia's barrels get more and more valuable each year.
A Little History
Modena started making Balsamic in the middle ages. It is always made in the attic, and wine is in the cellar. And, in old times, a battery was started when a girl was born and was given to the husband's family as part of the dowry when she was married.
You may see some balsamic carrying IGP and DOP designation. "IGP" is a commercial designation by the Modena Consortium, and is allowed to be mixed with wine vinegar, colorings, and caramels.
"DOP" is only made from grapes in the traditional method, and is in barrels for a minimum of 12 years. Ours is a DOP production, but bottled at 6 years. It has the same quality and production standards indicated by DOP, but is not aged as long, and so it is a fraction of the price.