Bring 4 cups (960ml) water in a medium sized saucepan to a boil. Add salt and stir until dissolved. Remove and allow the salt solution to cool completely.
Rinse eggs and place in a jar with lid. Set aside.
When salt solution is completely cool, add Shao Hsing cooking wine.
Pour salt solution into jar containing rinsed eggs.
Filled a small Ziplog sandwich bag half full with water. Squeeze as much of the air out as possible. Gently stuff bag with water into the jar to weigh down the eggs so that they are totally submerged.
Cover jar with lid and place jar in a cool spot at room temperature for 4 to 5 weeks. Chicken eggs will take 4 weeks while duck eggs should be left in the brine for 5 weeks.
After 4 to 5 weeks, do a test to see if eggs are ready. Remove an egg from the brine and crack into a bowl to check its yolk. It is ready if the yolk is a bright yellow-orange color and is quite firm to the touch. The white should be a little cloudy but still runny.
Alternatively, remove an egg from the brine and place it in a small saucepan covered with cold water. Boil over medium heat for 15 minutes. Egg is ready if it is salty and the yolk is a bright yellow-orange color.
If eggs are not ready, leave them in the brine for another week. Finally, remove all eggs from brine and store in a container in the refrigerator.