Garum was a type of thin Roman fish sauce, consisting of salted whole fish, that was allowed to ferment and drained of its brine. Its distinct flavor was used ubiquitously in Roman cooking.
Garum is sometimes used interchangeably with the word liquamen. 
The process of making garum also created other Roman condiments and dishes, including the fish sauce allec 
that was used as a less expensive substitute for garum, and Salsamentum, or "whole salted fishes". 
The main sources for descriptions of garum are from Apicus, and from the agricultural series Geoponica.
The ancient Roman process of making garum is markedly similar to the same process that is still being used to make fermented fish sauces in Southeast Asia.
Garum factories, "the only large-scale factory industry in the ancient world" 
where most often found near the sea to take advantage of the fishing industry, and to distance the factories' infamous stench of rotting fish.
Notable factories were located in southern Spain, and near the Black Sea.
To make the garum, small fish were placed in a vessel, and allowed to ferment for a period of time usually uncovered and in direct sunlight. The length of fermentation depended on the type of fish, and desired quality of the sauce, usually between one to three months. After which time, the resulting mixture would be strained at least once via a woven basket, thus separating the fish remains, called alec, and the thin, clear liquid. This brine was the garum itself, and what was used in cooking.
The garum before serving was sometimes mixed with herbs such as oregano or roe, vinegar, and/or wine.
Fish Used in Garum
Many different types of fish were used in garum preparation including but not limited to "prawns, sardines, mackerel, anchovies, tuna, slamon, red mullet and oysters among other sea creatures." 
Note that oysters are included in this list, meaning that fish were not the only seafood used.
Major Types of Garum
A type of garum made by the people of Bithyi that was usually made from anchovies, mackerel, bonito fish, or allec, flour, salt, and sometimes wine. It was allowed to be fermented in the open for two to three months before consumption.
Garum that was prepared in accordance with Jewish dietary laws (i.e. Kosher).
A type of garum made from a mixture of mackerel, roe and blood.
This garum originally came from Carthage, and was arguably the most famous of all garum types. Its name translates from the Latin as "garum of companions"; illustrating its unique and costly preparation. The mackerel used to produce this sauce would have been drowned in even more garum during its fermentation, thus making the sauce doubly strong. According to Pliny, it was "the most highly prized", and its cost was among the highest for any liquid at the time.
According to the agricultural book Geoponica, the garum referred to as Haimation was among the very best. It was made from the innards of tuna with salt, and allowed to ferment for two months.
If garum was needed immediately, the fish was boiled, and not allowed to ferment at all, but this type was considered very inferior to the ancients.
While not common, modern versions of garum can be found most often in Asian markets, names including but not limited to nam pla in Thai, tuk trey in Cambodian, and nuoc nam or nuos-nam in Vietnamese. In modern day Italy, there is a variation of garum made called collata that is available. Finally, there is a Japanese fish sauce called gyosho, but it is exceedingly rare.
When a fish sauce substitute cannot be found, either salt or a mixture of salt and anchovy heated in olive oil, and then mashed up can suffice. Researchers warn however that anchovies, or anchovy paste alone is not an appropriate substitute. Also, some contemporary cooks suggest decanting the sauce, and/or adding herbs before usage.
- Dalby, A. et al., The Classical Cookbook (J. Paul Getty Museum, 1996), ISBN 0-89236-394-0, pp. 19-22
- Faas, Patrick. Trans. by Whiteside, S., Around the Roman Table (Palgrave Macmillian 2003) ISBN 0-312-23958-0, pp. 142-146
- Ricotti, E., Dining As A Roman Emperor (L'Erma di Bretschneider 1995) ISBN 88-7062-901-5, pp. 11, 12
- ↑ From Geoponica, "Garum, sometimes called liquamen"
- ↑ The translator J.D. Vehling was of the opinion that liquamen was in fact a catch all term for broth or stock, and not necessarily a synonym for garum. Roman culinary researcher Patrick Faas counters that this is due to the fact Apicus originally meant "a solution of garum in water", and not stock per se
- ↑ Also known as hallec or alex
- ↑ Eventually salsamentum would come to refer to anything salted.
- ↑ Dalby, pp. 19
- ↑ Faas, pp. 144
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