These are the official indication on the label important to check when buying the balsamic vinegar of Modena:
DOP (Denominazione di origine protetta) indicates the traditional product under strict quality regulations and certified by the Consortium of Producers of Traditional Balsamic of Modena. Only two types of balsamic vinegar may carry the DPO indictation: Traditional Balsamic Vinegar of Modena (Aceto Balsamico Tradizionale di Modena) and Traditional Balsamic Vinegar of Reggio Emilia (Aceto Balsamico Tradizionale di Reggio Emilia)
The Italian DOP indication is the same as the European Union’s PDO (Protected Designation of Origin).
The traditional vinegar (with DOP certificate) must be aged for at least 12 years but it is possible to find ones aged 25 years and more. The traditional vinegar may be only made from two types of grapes (Trebbiano, Lambrusco) by cooking the grape must, then fermentation and oxidation leading to a long aging process in wooden barrels.
This vinegar is sold only in two types of bottles, different for the one from Modena and one from Reggio Emilia, with color caps indicating the age. A typical price is around 130 USD for a bottle of 100 ml (3.4 oz).
PGI (Protected Geographical Indication) which is used by the European Union to indicate a food product produced within a specific geographical area. Also the indication IGP (Indication Geographique Protegee) is used for the same purpose. Vinegar of Modena with the indication of PGI or IGP does not conform to strict quality norms and may be produced by an industrial process involving mixing grape must with wine vinegar and possible caramel for color. The minimum aging requirement is here 2 months. This vinegar may be quite inexpensive, just 3 USD per bottle. Some balsamic vinegars of Modena may be produced by a semi-traditional methods involving a long aging process, even 12 years but they lack the DOP certificate and strict controls of the consortium. Prices of the better ones can be in the range of 30 to 40 USD.