Garum

Weigh the fish whole and ungutted — the viscera carry the proteolytic enzymes that do the work — and rinse off surface grit. In a non-reactive vessel (glazed crock, glass, or food-grade plastic; never bare metal) layer the fish with the salt, beginning and ending with a generous layer of salt and crushing the fish lightly so flesh and guts mingle. The salt must be at least 25 to 30 percent of the fish weight: this is the food-safety line, high enough to suppress Clostridium and putrefying bacteria while still allowing the fish's own enzymes and salt-tolerant microbes to slowly autolyze the flesh. Anything less and it rots rather than ferments.

Scatter the oregano, dill or fennel, cracked coriander, and bay through the mass — the Roman recipes call for aromatic herbs both for flavor and, they believed, to temper the smell. If using, pour in the splash of old wine or fish stock to help the brine form. Pack everything tightly into a clean jar, press out air pockets, and set a weight (a brine-filled bag or a sanitized stone) on top so the solids stay submerged once the brine rises. Cover loosely with cloth or a loose lid that lets gas escape but keeps insects out. The fish must stay under brine the entire ferment; anything that bobs above the surface can mold.

Set the jar in a warm place — the Romans used full Mediterranean sun for one to three months; indoors, hold it at a steady 30 to 40 C (a warm cupboard, near a radiator, or a low dehydrator) for 2 to 3 months. Each week, open it, let the gas off, and gently stir or push the solids back under the brine. Over the weeks the fish enzymes (and salt-tolerant bacteria) digest the protein: the flesh slumps, breaks apart, and finally dissolves, while the liquid darkens from cloudy gray to a clear walnut-amber. The classic Apicius shortcut held it hot in sun for as little as 20 to 30 days; a cool spot can take 6 months or more. It is done when the solids have largely liquefied and the smell turns from raw-fishy to deeply savory and brothy.

Ladle the clear top liquor off the sediment, then strain everything through a fine sieve lined with several layers of cheesecloth or a clean cotton cloth — the Romans called this clarified pour-off liquamen, and the spent solids left behind were the cheaper allec paste. For a crystal-clear, glossy garum, strain twice and let it settle so any fines drop out. Optionally simmer the strained liquid gently for a few minutes and skim to pasteurize and concentrate it. Bottle in a clean sealed jar. The finished garum is intensely salty and savory; use it by the teaspoon as Rome did — to season sauces, braises, greens, and even sweet dishes — where it melts in as pure, invisible umami. It keeps for months to years in the fridge thanks to its salt.