Traditionally Balsamic vinegar is made from cooked Trebbiano and/or Lambrusco grape which have been pressed and then reduced by heat in an open vat for some 24 to 36 hours. The raw material of this cooked grape must having a content of soluble solids (above all glucose and fructose) ranging from 20 to 60°Bx and pH values of 2.3–3.2.
As with other vinegars, it is obtained by a two-stage fermentation process. In the first one fermentable sugars are converted into ethanol by yeasts obtaining ethanol content between 4 and 10%.
While in the second stage, AAB (acetic acid bacteria) oxidize the ethanol to acetic acid. Both stages occur by spontaneous fermentation. The process is carried out through a set of 5/7 wood barrels arranged in a series of decreasing volume that are open to the elements with a small rectangular hole in the top of the barrel. Barrels are traditionally made from Cherry, Oak, Mulberry, Ash and Juniper wood.
A volume of final product is withdrawn from the smallest barrel (barrel 1) and replaced with equal volume of product from the barrel immediately preceding in the set, the same is done for each intermediate barrel; the first one (barrel 5) receives new cooked must. This procedure, known as to “refilling”, is done once per year. The production and maturation process can take up to 12 years to complete and are subject to legislative supervision and approval.
Manufacturing of balsamic vinegar
