The preparation of the balsamic vinegar begins with the pressing of the grapes in wine-making vats. The must which is produced is boiled over a slow heat until its volume has been reduced by approximately half. Subsequently, it is chilled and transferred to casks that are made from different fine woods and come in a sliding scale of sizes. The casks are 70% filled. After a year, the must is racked to a smaller cask and the same process takes place in the following years. The casks used for the slow acetification caused by the natural fermentation and gradual concentration of the product are traditionally kept in the attics of houses, where it is very cold in the winter and extremely hot in the summer