This phenomenon in a bottle harks back to the oldest sort of wine, made in a time before stainless steel and temperature control. All of the greatest wines of antiquity, from the earliest mentions in Greek and Roman texts, all the way up to the 1820s, were made like this. After the harvest and initial vinification, Rancio wines age in barrel or glass demi-john for up to several years in a place where weather can get to it. It gets cold. It gets hot. It evaporates and concentrates and changes with the seasons. The result is a densely aromatic, richly flavored wine not entirely unlike Amontillado Sherry, a key to a whole other galaxy of wine flavors; caramelized, nutty, savory and zesty.