Aging wine: read the cask before breaking it
A keg makes wine. A cask improves wine that already exists. If your fruit or wine will not go in, check the machine, room and item in that order.
Load finished wine in the farmhouse cellar
Collect the bottle from the keg. Take it down the cellar stairs and use it on an empty cask. A cask placed in a shed does not age wine in the standard game. If you are holding raw fruit, use a keg first; jelly belongs in neither stage of a wine-aging batch. Leave yourself an aisle so you can see which casks are available before spending a whole stack of wine.
Count stages from the day you loaded it
For ordinary-quality wine, silver arrives after 14 days, gold after 28 total and iridium after 56 total. Mark the loading day and the intended pickup day together. For example, an ordinary bottle loaded on Spring 1 reaches silver on Spring 15, gold on Summer 1 and iridium on Fall 1 if left uninterrupted. A quality star on the cask indicates its contents have reached that stage; it does not mean maximum quality.
Choose between an early sale and a long batch
For a finished iridium bottle, interact with the ready cask normally. To stop at silver or gold, strike that cask with a suitable tool such as the axe, then pick up the ejected wine and check the star before loading another bottle. Do not dismantle an entire packed cellar simply to inspect one sample. If you plan to sell most wine immediately, reserve a reachable row for the portion you can leave tied up.