A style of vinegar that lies somewhere between ordinary wine vinegar and balsamic vinegar is the solera-aged sherry vinegar of Spain. This starts from the young sherry wine, which contains no residual sugar. Like sherry wines and balsamic vinegars, sherry vinegar is blended with older batches and matured for years or decades in a series of partly-filled barrels. The concentration by evaporation, and extended contact with microbes and wood, leave sherry vinegar with high levels of savory amino acids and organic acids, and viscous glycerol. In old soleras, the acetic acid concentration can reach 10% and more. Sherry vinegar isn’t as dark and savory as balsamic vinegar, but is noticeably more intense and nutty than other wine vinegars.