Keto-friendly pickled herring ("sill")

This is my recipe for Swedish "sill" that is keto friendly. Regular sill uses a ton of sugar in the brine, this replaces it with erythritol to have a safe sweetener in there, instead.

Equipment:

• small saucepan
• sealing pickling jar (size 13, 750 ml)
• knife, cutting board

Ingredients:

• cleaned, de-skinned herring fillets (~ 400-450g, usually about 6-7 decent-sized fillets)
• 1 small red or yellow onion
• 10 black pepper kernels (whole)
• 5-7 allspice berries (myrtle pepper/piment) (whole)
• 5 cloves (whole)
• 1 whole bay leaf
• 60-70g of granulated erythritol (to replace 90g of granulated sugar)
• 1/4-1/2 teaspoon of salt
• 1.5 dl of water
• 0.5 dl of clear, strong vinegar (12%). Adjust water/vinegar ratio if you can only find weaker vinegar.
• (optional but recommended) 1/4 teaspoon of (food grade) sodium benzoate to preserve
• small amount (few tablespoons) of carrot or red bell pepper to taste

Method:

1. Finely chop the onion and shred the carrot or bell pepper
2. Put the erythritol, salt, water, pepper kernels, allspice, bay leaf, cloves and sodium benzoate in a small saucepan. Do not add the vinegar yet!
3. Put on high heat to rapidly bring to a boil while stirring to dissolve everything. Take off the heat the moment it boils, do not let simmer too long. Cover with a lid.
4. After a minute or so to bring it down from boiling hot, add the vinegar, stir and then cover to prevent evaporation. Let cool to lukewarm (fridge safe, and so it won't cook the fish).
5. While the brine cools, rinse and cut the herring into 1.5-2 cm wide bits (across the length of the fish), and layer with the onion and carrot/bell pepper in the pickling jar.
6. When the brine has sufficiently cooled, carefully pour it into the filled pickling jar. Seal the jar.
7. Put it in the fridge or sufficiently cold storage (< 8 Celsius) and let it pickle. Recommended at least 2 weeks, but be careful if you didn't add a preservative (might need to eat it sooner in that case).

Notes:

If the liquid isn't fully covering the top bits of fish (it should!), make sure to turn and twist the jar now and then to carefully mix the jar's contents without opening the jar. You can also add a little bit more liquid but keep the water/vinegar ratio intact.
When breaking the seal after pickling, keep in the fridge and eat within 3 days.
Enjoy the sill as a traditional side dish or with breakfast!