A pickaxe can be used to remove artisan goods from a cask at any stage of fermentation.
Casks are able to produce items with "iridium star" quality. Iridium star is the highest level of quality, which doubles the value of an item. Different types of items take longer or slower to age. Wine takes the longest -- 2 seasons of aging to go from basic wine to iridium quality wine.
Casks can be placed anywhere, however they will only accept goods to refine if they are actually in the cellar.
You start with 33 Casks. It's possible to place 188 Casks in the Cellar, requiring 155 Hardwood and 3100 Wood.