Makes 18 cups
7 pounds freshly harvested moro oranges, washed and cut into slices ⅛ inch thick, seeds discarded
6 pounds sugar
¾ cup lemon juice, plus more if needed
Cut orange rounds into quarters. Place fruit in bowl and cover with water. Refrigerate overnight.
The next day, drain water from fruit and transfer to copper jam pan. Add fresh water to just cover fruit. Heat to boil, turn heat to low, and simmer 1 hour, stirring occasionally. Remove from heat, let cool to room temperature, then refrigerate overnight.
The next day, return the pan to the stove. Add sugar. Cook over moderate heat for 45 minutes, stirring intermittently. Adjust acidity by adding lemon juice to bring pH below 4. If you are not equipped to measure pH, add ¾ cup lemon juice. Cook additional 15 minutes, then check temperature. When temperature of marmalade is between 212 and 220 degrees F, put marmalade into sterile jars and process with your usual canning technique.