Wash shuck beans; discard any dark or discolored beans. Break shuck beans in half; place in a 6-quart pressure cooker with water to cover (about 6 cups). Cover and chill. Soak beans for 24 hours; do not drain. Bring to a boil, uncovered; reduce heat to medium, and cook 30 minutes. Drain and rinse beans.
Return beans to pressure cooker; add salt pork and, if desired, salt. Add 1 inch cold water to cover (about 4 cups) to pressure cooker.
Cover cooker with lid, and seal securely; place pressure control over vent and tube. Cook over medium-high heat 12 minutes or until pressure control rocks quickly back and forth. Reduce heat to medium low; cook 15 more minutes. (Pressure control will rock occasionally.)
Remove pressure cooker from heat; run cold water over cooker to reduce pressure. Carefully remove lid so that steam escapes away from you.
Note: For testing purposes only, we used a Mirro 6-quart rocker top pressure cooker. If you have another model, cook according to manufacturer's instructions.