Slice the pineapple. Lay the pineapple on a cutting board and cut off the top and bottom parts. Next, slice the pineapple into 1-inch thick slices. Cut off the peel and discard.Cut it into chunks. Slice each slice into quarters and set aside.
Simmer
Soak the shiitake mushroom. Place the dried shiitake mushroom in a small bowl and cover it with 3.5 ounces (100ml) of hot water. Let it rehydrate for about 5 minutes.
Transfer to a saucepan. Transfer the soaking water of the shiitake, pineapple chunks, and remaining water (19.5 ounces/550ml) to a saucepan.
Let simmer. Bring to a simmer over medium heat and let it simmer for 10 minutes uncovered.
Add the salt and simmer again. Next, add the salt, rehydrated shiitake mushroom, and sugar. Let simmer for another 35-40 minutes or until it has reduced to 11.7 ounces (330ml).
Strain
Strain the fish sauce using a fine sieve mesh and discard the pineapple chunks. You can now stir in the MSG, if using, and the dark soy sauce to give your fish sauce a beautiful golden brown color.
To store the fish sauce, transfer it to a clean glass bottle and keep it in the refrigerator.
Notes
Measure the liquid after simmering. It is essential to measure the amount of liquid left after simmering. You will need 330ml left in order to get the saltiness on point. If you have more, let it simmer for a few more minutes. If you have less, add water until it reaches 330ml.
Store in the refrigerator. While you could store it at room temperature, keeping it in the refrigerator is preferable to preserve its freshness.