Marine Invertebrate Fermentation Was Never Just About Food

Digital painting of giant sea clam

Fermentation is often thought of as one of the oldest and least aggressive technologies in the history of humankind. A slow and almost romantic process whereby microbes work their magic on milk to make cheese, on grapes to make wine, or on soybeans to make miso. However, marine invertebrate fermentation has never been gentle. Under the surface of each shrimp paste, fermented clam, or squid viscera is an invisible biochemical warzone where halophilic bacteria, proteolytic fungi, opportunistic pathogens, and molecular scavengers battle for supremacy in the decaying animal flesh. The term “fermented seafood” is a euphemism for a very carefully managed breakdown of biological material. The fermentation of marine invertebrates is more bizarre, more sophisticated, and more misunderstood than anywhere else.

Fermented fish has been the sole focus of global food culture for centuries. Historical fish sauces are dominated by Roman garum, Southeast Asian fish sauce, and Nordic fermented herring. However, fermented marine invertebrates such as crustaceans, molluscs, cephalopods, and echinoderms have received far less mainstream scientific attention, despite their equally long history. These are not just “fish without bones.” They are two distinct biological systems. The protein architecture, lipid chemistry, digestive enzymes, and resident microbiomes of squid viscera, shrimp exoskeletons, clam tissues, and sea urchin gonads are all radically different. As a result, their fermentation is not a conventional food preservation process, but rather an ecological engineering process for decomposing marine biomass.

This hidden complexity is embodied perfectly in traditional Indonesian terasi. To most people, it is merely a pungent block of fermented shrimp paste with an overpowering smell. But chemically, terasi is the result of an extreme microbial selection process under extreme osmotic stress. At concentrations of 20–30%, salt is lethal to most organisms, with only highly specialised halophilic microbes, like Tetragenococcus halophilus and some species of Bacillus, being able to survive. The whole microbial community is wiped out, but a small fraction survives in the salty remains. The flavour itself is not “created” by humans in the conventional sense. It’s a product of microbial metabolism under extreme osmotic pressure, breaking down shrimp proteins into glutamate-rich compounds that give rise to the sensation we know as umami.

But today’s food science is not content with nature taking its course. These ancient fermentations are being redesigned with the precision of synthetic ecology. Glucose is intentionally added as a metabolic incentive for lactic acid bacteria in low-salt shrimp fermentations. These microbes quickly use up the sugars, lower the pH, and inhibit the production of harmful biogenic amines, such as histamine. The fermentation period is reduced from months to days. What used to rely on seasonal uncertainty and inherited intuition is now programmable biochemistry.

Some interventions are even more bizarre. In experimental shrimp paste production, scientists have devised a sequential fermentation process using Cladosporium fungi as the first step to aggressively break down complex proteins, followed by Enterococcus faecalis as the second step for flavour refinement. One organism mellows the battlefield. The other one is in it. This is not a cooking lesson. It’s microbial succession as an ecological military campaign.

Things get even more perilous when it comes to bivalves like oysters and clams. Bivalves are filter feeders, unlike shrimp. They continuously filter the surrounding water, causing pathogens such as Vibrio species, marine toxins, and environmental contaminants to accumulate in their tissues. Under such circumstances, spontaneous fermentation can easily become unstable. Modern fermentation strategies therefore begin with what is essentially a microbial reset. Oyster tissues are sterilised and re-inoculated with carefully selected microbial consortia consisting of Saccharomyces cerevisiae, Kazachstania, and Lactobacillus pentosus. Designer communities of microbes are introduced to replace wild microbes, which are eliminated, and are optimised for flavour, safety, and competitive dominance. Seafood is no longer just being fermented by humans. They are creating micro-ecosystems.

Cephalopods add another layer of absurdity. Squid viscera, which can account for almost 20% of their body weight, are generally regarded as industrial waste due to their short shelf life and strong marine smell. However, recent fermentation studies have not looked at these organs as waste, but as biochemical gold mines. The viscera are partially digested at high temperatures with commercial alkaline proteases before fermentation even starts. Industrial enzymes pre-chew the tissue before bacteria can colonise it. Only then are special strains such as Bacillus tropicum and Acinetobacter guillouiae added to the substrate, where they quickly transform the decomposing organ matter into amino-acid-rich compounds that have surprisingly complex aromas, similar to malt, cheese and roasted meat. The odour of rotting is transformed into something edible.

The strangest of all may be sea urchin fermentation. Fermented sea urchin gonads are made in parts of Indonesia with the help of starfruit water containing oxalates, phenols and flavonoids. The fruit extract is a selective antimicrobial agent that inhibits the growth of spoilage organisms while promoting the growth of the protease-producing bacteria that dominate the fermentation. The outcome is an indigenous biotechnology system where plants are used to manipulate the marine microbial ecology with remarkable specificity. Selective microbial control was known to traditional communities before microbiology was even invented.

But what is so interesting about these fermentations is not just the flavour. It is the awareness that microbes are creating new biochemical organisms in marine tissues. Proteins are broken down into bioactive peptides that have antihypertensive activity during fermentation. Some bacteria can break down glutamate into γ-aminobutyric acid (GABA), a neuroactive substance that has been linked to blood pressure control and neurological effects. Certain microbial communities can decrease the allergenicity of shellfish by enzymatically breaking down the IgE-binding epitopes of tropomyosin, the protein that is the primary cause of shellfish allergies in humans. Fermentation is no longer about preservation. It is molecular surgery done by microbes.

However, the most disturbing notion that has come out of this field is a concept known as microbial heritage transfer. Traditional marine ferments are often based on endangered or ecologically sensitive species. Some of the giant clams, some sea cucumbers and rare molluscs are becoming more and more vulnerable to over-exploitation. It is now thought that the real source of these foods might not be the animal itself, but the microbial consortia and biochemical changes that occur during fermentation. Theoretically, the microbial community of an endangered species ferment could be transferred to abundant and sustainable substrates, maintaining much of the original flavour chemistry. The memory of a food may persist even after the organism is gone. Somehow, that feels very sad.

This alters the definition of fermentation completely. It is no longer viewed as a slow decomposition caused by salt. It turns into a repository of ecological knowledge in the form of microbial interactions. A biochemical inheritance system that was transmitted from generation to generation, but no one fully understood the organisms that transmitted it. The future of marine fermentation might thus be somewhere between the old and the new, and between systems biology and ecological conservation. Not because microbes are simple. However, they were never easy to start with.