The hermetic seal is formed when the top lid is placed upon the body of the can (which had been filled with beans) and this is pressed together by the equipment to form what is termed a double seam.
The closing equipment must be precisely set to ensure the proper folds are made. Closing machines are often operating at 200 to 500 (or higher) cans per minute with the machine having numerous sealing heads. If one head is misaligned even slightly, an imperfect seal may be formed. Cans from each sealing head are tested throughout the day by tearing the seal about and measuring the amount of overlap within the fold and thickness of the fold.
https://www.fda.gov/safety/recalls-market-withdrawals-safety-alerts/faribault-foods-inc-announces-voluntary-recall-limited-quantity-sw-brand-organic-black-beans-and-o
Faribault Foods, Inc. Announces Voluntary Recall of a Limited Quantity of S&W Brand Organic Black Beans, and O Organic Brand Black Beans and O Organic Brand Chili Beans Due to Compromised Hermetic Seal
Summary
Company Announcement Date: April 21, 2021
FDA Publish Date: April 22, 2021
Product Type: Food & Beverages Organic Food / Home Grown
Reason for Announcement: Potential for Clostridium Botulinum
Company Name: Faribault Foods, Inc
Brand Name: S&W and O Organic
Product Description: Organic Black Beans and Organic Chili Beans