Trim stems and discolored parts. Soak 10 minutes in cold water to loosen dirt; wash in clean water. Leave small mushrooms whole and cut larger ones.
Cover with water and boil 5 minutes. Pack hot mushrooms, leaving 1-inch headspace.
Add optional salt and fresh hot water, maintaining 1-inch headspace.
Pressure process half-pints or pints for 45 minutes.
Dial gauge: 11/12/13/14 psi by 2,000-ft altitude bands through 8,000 ft. Weighted gauge: 10 psi through 1,000 ft; 15 psi above.