On riddling racks the booze is stored - these racks are used to collect sediment from the second fermentation of sparkling wine made in the traditional champagne style.
Before, the wine goes through the primary fermentation in stainless steel tanks and then is bottled along with a mixture of yeast and sugar for the secondary fermentation that takes place within the bottle. It is this second fermentation which produces the bubbles.
After the second fermentation the wine is stored horizontally for weeks or months. Contact with the yeast adds complex and flavors. The sediment is then collected through a process known as riddling, which you see here. This involves turning the bottles every few days over a period of weeks or months. The sediment is then removed and you have your spumante or prosecco.