Basically sounds like the same idea as Thai or Vietnamese fish sauce, but with Mackerel rather than anchovies.
I'm confused by this recipe on many counts.
Unless I'm just missing it, I don't see a QTY for the white wine you call for in the directions, and, even without it, that is a huge qty of highly flavored chopped aromatics. Especially if you are only adding a few drops of the garum. Even allowing for reduction, 7 cups of chopped vegetables is going to make a big batch of "sauce, " with or without the addition of an unspecified qty of white wine.
I'm confused by this recipe on many counts.
Unless I'm just missing it, I don't see a QTY for the white wine you call for in the directions, and, even without it, that is a huge qty of highly flavored chopped aromatics. Especially if you are only adding a few drops of the garum. Even allowing for reduction, 7 cups of chopped vegetables is going to make a big batch of "sauce, " with or without the addition of an unspecified qty of white wine.