While I don’t find the thought of a sauce based on fermented fish entrails particularly appetizing, the Greeks and Romans both loved garum, the quintessential seasoning of Roman cuisine. Despite their mode of preparation, the modern versions that are popular in Southeast Asian cuisines are actually quite tasty.
Garum and liquamen are used in the majority of recipes in Apicius’s cookbook, which is believed to have been compiled for the use of Roman chefs between the first and third centuries AD.
The original form of garum used shrimp (Latin garus), according to Pliny, but later versions used a variety of other fish. The intestines of fish were softened (macerated) by soaking in water saturated with salt until they began to putrify. Then vinegar and herbs, such as parsley, were added. Another variation let entrails and other fish parts liquefy in salt.
By the time of Pliny, mackerel was the preferred fish for making the best garum. Its entrails and gills and sometimes the blood were collected from freshly caught fish. The most highly regarded mackerel-based garum came from Spain and was called garum sociorum (garum of the allies).
In another expensive variation, the blood and entrails of a tuna were combined in a container and left for two months. A hole was then punched in the bottom to permit the garum to drain out and be collected.
Anchovies were also a popular source of liver that was softened in vinegar with pepper, salt, garlic, white wine, and sweet herbs. For true gourmets, garum from the liver of the red mullet was considered beyond compare.
Garum for the poorer classes was made from the intestines of the small fish that lived among the shoreline rocks. Sometimes the whole fish were placed in a container with a lot of salt. The container was left in the sun for two or three months until fermentation turned its contents into a liquid paste.
If garum was needed immediately, salt was added to filtered brine until an egg would float on it. The fish components and wild marjoram were added. This was boiled over a low fire until the fish parts dissolved completely. Wine that had been reduced in volume by 2/3rds by boiling was then added. After cooling, the liquid was filtered several times until it was clear.
Garum was used as a seasoning in small quantities, much like one might use a small amount of Worcestershire sauce. Other cuisines that use fermented fish sauce include Thai (nam pla), Vietnamese (nuoc-mam), Cambodian (nuoc-mam and nuoc-mam-gau-ca), Laotian (nam pla), Philippine (patis), Indonesian (ketjab-ikan), and Malaysian (budu). These should prove suitable substitutes for garum in Roman recipes.
If you want to try making your own garum, some modern recipes can be found at https://coquinaria.nl/en/roman-fish-sauce/.
Apicius. Cookery and Dining in Imperial Rome. Edited and translated by Joseph Dommers Vehling. New York: Dover Publications, Inc. 1977.
Soyer, Alexis. Food, Cookery, and Dining in Ancient Times: Alexis Soyer’s Pantropheon. Mineola NY: Dover Publications, Inc., 2004.