To vacuum seal a Mason jar, use a vacuum sealer with a specialized vacuum port. Machines usually come with attachments for vacuum sealing, though they are also available to purchase separately.
The Mason jar must have at least an inch of empty space below its mouth to prevent the machine from sucking food inside it. Cover the mouth of the jar with its flat lid, and set aside the accompanying metal ring. Fit the jar sealing attachment by firmly pushing it over the jar’s closed mouth to cover the neck of the jar. Connect the ends of the tube into the right positions, and ensure a good fit. Press the button on the sealer to start the air extraction process.