Red wines are fermented with the grape skins and seeds at warmer temperatures than white wines. The skins float to the top forming a cap during fermentation and must be moistened regularly with juice to extract color and flavors. Red wines are usually fermented for a period of five to ten days and then are filtered, clarified and preserved with the addition of sulfites. It is common for red wines to be aged in oak barrels for a period of about one to two years. As with whites, the vintner may choose to blend at this stage. The wine is then finished, filtered, and clarified before bottling. In some rare but important instances, generally among small, ultra-premium wineries, no or only minimal fining and filtering is carried out in an effort to capture the maximum amount of natural flavor components.