Cut the whole mackerel into 5 cm chunks and add to a big, glass sealable jar. Add everything, including the heads and guts.
Mix the fish with an immersion blender. Yes blender :).
Smash the garlic and add to the jar together with the other spices.
Cover the fish mush with the filtered water and mix well.
Close the jar and make sure is securely fastened so no insects can get inside.
Fermentation process
Store the jar in a cool, dark place away from direct sunlight. We made fish sauce in november and stored it in a large bag on the terrace.
Let it ferment for 1 month and make sure to burp it the first few weeks to precent any pressure build up.
Finishing the sauce
Strain the contents of the jar through a fine mesh strainer and let it seep through for 30 minutes to make sure all the liquid has run through. Discard the solids.
Pour the strained fish sauce through a coffee filter set inside a funnel inserted into a jar or glass bottle. This process takes a while, so we setup multiple bottles with a funnel to speed it up. Keep an eye on it and make sure the coffee filter doesn't break, because then you have to start over. It took us about 8 hours to filter this amount, which results in about 1/2 liter of finished sauce. The end result should be a clear, caramel coloured liquid with a pungent smell, yet a very subtle, almost sweet taste.
Store your homemade fish sauce in the refrigerator and it will last for years!