Liquamen is a fish sauce that was used in Roman cuisine as soy sauce is used in Asian cuisine. Liquamen is notably present in the recipes of Apicius as salt is notably absent. Flowers and Rosenbaum state that it was "used in lieu of salt". Vehling, however, describes it as "any liquid appertaining to or derived from a certain dish or food material." Vehling goes on to describe another fish sauce called garum. Flowers and Rosenbaum considers garum to be just another name for liquamen. In either case, each is described as a sauce made from fermented fish. I am more inclined to agree with Flowers and Rosenbaum's interpretation mostly due to the lack of salt mentioned in Apicius' recipes. Flowers and Rosenbaum even give several recipes for the preparation of liquamen as quoted from the Geoponica., one of which is as follows:
The so called liquamen is made as follows: the entrails of
fish are thrown into a vessel and salted. Take small fish, either
atherinae, or small red mullet, or sprats, or anchovy, or any other
small fish, and salt all this together and leave to dry in the sun,
shaking it frequently. When it has become dry from the heat extract the
garum from it as follows: take a long fine meshed basket and place it
in the middle of the vessel with the above mentioned fish, and in this
way the so called liquamen, put through the basket, can be taken up.
The residue is allec.
Each dish that was made for the Roman course for Jingles originally listed liquamen as an ingredient, but for dietary concerns salt was substituted instead in all dishes except for the Grilled Red Snapper in Red Wine Sauce. However, I did not have the means nor the desire to make the liquamen as described above. Fortunately, Flower and Rosenbaum also list another recipe from Geoponica on a quick process for making liquamen:
If you wish to use the garum at once i.e., not expose it to the sun, but boil it make it in the following manner: Take brine and test its strength by throwing an egg into it to try if it floats; if it sinks the brine does not contain enough salt. Put the fish into the brine in a new earthenware pot add origan, put it on a good fire until it boils i.e., until it begins to reduce. Some people also add defrutum. Let it cool and strain it two and three times, until it is clear. Seal and store away.
The following is my redaction of the above "quick process" recipe:
1 ½ cup water
Directions: Combine ingredients in a 1 quart pot. Boil until rendered by half. Strain until clear. Store in sealed jar until ready for use. Yields 1 ½ cups.
The Roman Cookery Book translated by Barbara Flowers
and Elisabeth Rosenbaum, Peter Nevill Limited, 1958.
Cookery and Dining in Imperial Rome, edited and translated
by Joseph Dommers Vehling, Dover, 1936.