Excuse the length of these musings, but I think that the garum discussions were very interesting, and I hope they will continue. I thought, however, that I would start a new thread, because the one on Garum, semi-putrid shellfish, etc, has gotten so long. All cultures eat rotten foods. It is both a way of preservation, and of enhancing flavors, though these are often very acquired tastes. Frank McGee has a great discussion of this in his book in a sectional called "Aversion to Cheese." He writes that by allowing certain, somewhat more benign micro-organisms to act on food and begin to break it down, more harmful microbes have a difficult time of establishing themselves, thus preserving the food. It is easier to keep a cheese that milk; or fermented fish paste than fresh fish. By breaking down some of the proteins, etc., a whole host of aromas and flavors are released, some of them quite strong.
I also think that it is not only food, but salt that needs preserving. We grew up with Morton's "If it rains, it pours" but in tropical climes, salt is apt to be a magnet for all kinds of moisture and things in it. There is a great passage about this in Naipaul's A House for MR.Biswas. The Indian family visits the house of Mr. Biswas' Anglo boss, and the boy is very impressed with the fine salt that pours freely -- not something generally avaailble in the caribbean. Perhaps putrid salty things -- fish sauce, soy sauce, cheese, kishik, are a way of transporting salt in some tasty form, and one that ultimately gives shape to a cuisine. I wonder if the uses of garum/liquamen in Ancient Rome are all that different from that of parmiggiano regianno cheese today?
All cultures use this kind of preservation in some degree or other. The aversion of most Americans to the range of preserved fish flavors in other, particularly Asian, cuisines, is matched by their aversion to many of our preserved foods, esp. cheese. Once, I was in a Cambodian house, and smelled the most pungent rotting fish smell I have ever smelled in my life. It was a fermented fish paste, wrapped in a banana leaf and grilled. "Cambodian cheese," my hosts explained. These are apparently tastes best and most easily acquired at a relatively young age -- though how many of us chowhounds began to relish fish sauce and fermented shrimp sauce before our 20s?
I remember being at a pot luck dinner, where one of the Chinese guests reacted violently to the macaroni and cheese. "Why would anyone want to ruin a good dish of noodles with salty, rotten milk?" Not that different than our first reactions to a Southeast Asian shrimp paste. And even how many of us will dip some fried meat into shrimp sauce thinned only with a bit of lime, as much as we may relish these flavors when disguised a bit.