The purpose of adding fish sauce to recipes is to add umami, or depth of flavor and savoriness. Most umami-rich foods are animal based, such as bacon or fish or parmesan cheese. But there are also several vegan friendly foods that contain a lot of umami, such as seaweed, mushrooms, and miso. Fermented foods are especially loaded with umami, so soy sauce is high on that list as well.
The recipe for vegan fish sauce below is based on these ingredients and its the best one I've found so far to replace fish sauce in vegetarian/vegan recipes. If you can't find mushroom soy sauce, add a few dried shiitake to the seaweed mixture in the beginning.
Vegan Fish Sauce
(makes about 3 cups)
1 1/2 cups shredded seaweed (I use wakame)
6 cups water
6 fat cloves garlic, crushed but not peeled
1 T peppercorns
1 cup mushroom soy sauce
1 T miso
Combine wakame, garlic, peppercorns and water in a large sauce pan and bring to a boil. Lower heat and simmer about 20 minutes. Strain and return the liquid back to the pot. Add soy sauce, bring back to a boil and cook until mixture is reduced and almost unbearable salty. Remove from heat and stir in miso.
Decant into a bottle and keep in the refrigerator. Use one-for-one to replace fish sauce in vegan recipes.
Note: You should be able to find wakame in most health food and Japanese grocery stores. Its also readily available online.
(Image: Dana Velden)