How Everything Is Made on Instagram: "How wine bottles are sealed Wine bottles are sealed using either corks or screw caps, and both methods are designed to protect the wine from leaks, contamination, and premature oxidation. With cork sealing, a natural or synthetic cork is made slightly wider than the bottle’s neck. During bottling, a machine compresses the cork, inserts it into the opening, and releases it. Once inside, the cork expands back to its original size, forming a tight seal against