Grape must

Must (from the Latin vinum mustum, "young wine") is freshly pressed fruit juice (usually grape juice) that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace; it typically makes up 7–23% of the total weight of the must. Making must is the first step in winemaking. Because of its high glucose content, typically between 10 and 15%, must is also used as a sweetener in a variety of cuisines. Unlike commercially sold grape juice, which is filtered and pasteurized, must is thick with particulate matter, opaque, and comes in various shades of brown and/or purple.

The length of time that the pomace stays in the juice is critical for the final character of the wine. When the winemaker judges the time to be right, the juice is drained off the pomace, which is then pressed to extract the juice retained by the matrix. Yeast is added to the juice to begin the fermentation, while the pomace is often returned to the vineyard or orchard to be used as fertilizer. A portion of selected unfermented must may be kept as Süssreserve, to be added prior to bottling as a sweetening component. Some winemakers create a second batch of wine from the used pomace by adding a quantity of water equivalent to the juice removed, letting the mixture sit for 24 hours, and draining off the liquid. This wine may be used as a drink for the employees of the winemaker or as a basis for some pomace brandies. Grappa, however, by law, must be produced only from the pomace solids, with no water added. The must can be used also for Balsamic Vinegar production, the special vinegar from Modena (Italy): for the acetification is use a selected bacterial colonies or the lenta in superficie (slow surface) or lenta “a truciolo” (slow wood shavings) methods and then there is a maturation phase. Both the acetification and maturation take place in precious sessile oak, chestnut, oak, mulberry and juniper barrels. The minimum maturation time is 60 days and after this period a group of expert technicians test analytic and organoleptic resulting product.

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