Patience is a virtue in Modena. Like superb Parmigiano Reggiano, great aceto balsamico takes time. It takes years for wine grapes to transform themselves into the dark, suave and silky aceto balsamico di Modena, a condiment and cooking ingredient now prized worldwide. As with fine wine, production begins in the vineyards of Modena and Reggio Emilia, with the harvest of plump, sun-ripened clusters. Regulations permit the use of seven local grape varieties, but the red Lambrusco and Sangiovese and the golden Trebbiano are the most important.