Case Study 1. The Three-Year Crock — Aroon's Fish Sauce

Mae Som ("The Mother's Kitchen") sits on a quiet stretch of Bloor Street in Toronto's Annex neighborhood. The dining room holds twenty-eight seats. The menu changes by season, but the soul of the place — the salty-sweet-sour-bitter-umami balance that Aroon Sornprasit learned at his grandmother's table in Chiang Mai — does not change. And the soul of that balance, Aroon will tell you, is fish sauce. Not fish sauce from a bottle. Fish sauce that he has made.

In a windowless room behind the kitchen, on a wooden shelf, sits a stoneware crock about the size of a small suitcase. It has a heavy ceramic lid, weighted with a flat river stone Aroon brought from the Mae Ping. The crock is not labeled, but Aroon knows what's in it. He started this one in late autumn, three years ago. Inside is approximately thirty kilograms of small whole anchovies — sourced from a sustainable supplier in Nova Scotia, which is the closest Aroon could come to the Gulf of Thailand at his current geography — packed in a 3:1 ratio with non-iodized sea salt. The fish were never gutted. The salt was layered between the fish in alternating bands. The crock was sealed and weighted on day one, and from that moment until eighteen months in, no human touched it.

Around month eighteen, Aroon began siphoning a small amount of the dark amber liquid that had drained to the bottom of the crock. This is the first press fish sauce — the most concentrated, most prized, most intensely flavored portion. He racked it into glass demijohns and let it age further in a dark cabinet. Now, at month thirty-six, he has about twelve liters of nam pla that has aged for three years in two stages — eighteen months in the original crock, eighteen months in glass.

This case study is about what happened in that crock, microbiologically, biochemically, and how it makes the sauce taste the way it does. It is also about something harder to teach: the relationship between Aroon's grandmother's knowledge and the modern food-microbiology literature, and what it means to honor a tradition you are descended from while explaining it in scientific language.

The microbial story

Fermented fish sauces — nam pla in Thailand, nước mắm in Vietnam, patis in the Philippines, padaek in Laos, aekjeot in Korea, shottsuru in Japan, the Roman garum of antiquity — are made by salt fermentation of small whole fish. Salt at concentrations of 20–25% by weight of fish does several things at once. It draws water out of the fish through osmosis (Chapter 3), creating the brine that becomes the sauce. It dramatically reduces the water activity of the system — to aᵥᵥ ≈ 0.75 or below — which inhibits most pathogenic and spoilage bacteria. And it selects for halotolerant and halophilic bacteria — salt-loving organisms that are more or less dormant in fresh food but thrive in heavy salt.

The dominant microbial community in a long fish sauce ferment, characterized in research over the past two decades, includes:

• Tetragenococcus halophilus and T. muriaticus, both halophilic LAB. These are not the Lactobacillus of sauerkraut — they are specialized salt-loving relatives that thrive at salt concentrations that would inhibit Lactobacillus. They contribute lactic acid, slowly, over months.
• Halanaerobium species, anaerobic halophilic bacteria that contribute to certain volatile compounds, particularly some of the characteristic sulfur notes.
• Various halophilic archaea (single-celled organisms that are technically a different domain of life from bacteria, though similar in size and metabolism), present in small numbers.

The salt-tolerant microbial community is not the only thing at work. The fish's own enzymes — particularly the proteases in the gut and the muscle tissue — remain active even at high salt and slowly break down the fish proteins. The protein breakdown is the headline event. Over two to three years, the fish proteins are progressively hydrolyzed to peptides and then to free amino acids. By the end of a long ferment, the sauce contains approximately 18–22 grams of nitrogen-containing compounds per liter, the great majority of which are present as free amino acids.

The amino acid profile of a long-aged fish sauce is extraordinary. Glutamate is the headline — the umami amino acid (Chapter 6) — and it is present at concentrations far higher than any unfermented food can produce. Aspartate (also savory), alanine (slightly sweet), glycine (sweet), and lysine (broth-like) are also abundant. The flavor is complete protein flavor — the molecular signal of well-rested cooked meat broth — packed into a clear amber liquid that you can splash on a bowl of rice noodles.

Volatile compounds — what gives fish sauce its characteristic, polarizing aroma — include several dozen molecules characterized in modern analyses. The signature notes include:

• Trimethylamine (TMA) — the "fishy" smell, slightly polarizing to the unfamiliar nose, but in context an essential top note.
• Various sulfur compounds — methanethiol, dimethyl sulfide, dimethyl trisulfide — contributing the deep savory base notes.
• Short-chain fatty acids — butyric, isovaleric, propionic — contributing barnyard, cheesy, and complex notes.
• Ester compounds — methyl esters and ethyl esters of various fatty acids — contributing fruity high notes and rounding the profile.

The result, at three years, is not "fishy" in the way a tasting-novice might expect. It is layered. The sip of the spoon at three years has the savory force of consommé, the brightness of a well-aged cheese, a faint sweetness, a sustaining length on the palate, and the mineral undercurrent of the sea. It is what time and patience and salt and small fish can do.

Aroon's grandmother

Grandmother Sornprasit (Aroon will not say her first name in print — there are reasons rooted in family privacy that he has asked be respected) made fish sauce her whole life. She made it in the back of her noodle stall in Chiang Mai, in clay pots that her own grandmother had used. She did not call the bacteria by name, because no one in her household had ever heard the names. She called the process kan-mak — "the seasoning" — and she could tell, from the smell, when a pot was finished. The good ones smelled like the river after rain, she said.

Aroon, when he came to Canada at nineteen, brought no fish sauce with him. He brought, instead, the principle: small fish, lots of salt, time, patience, never disturb the pot. When he opened Mae Som at twenty-eight, he started his first crock. It failed — he overpacked the salt, used the wrong fish, lost the whole batch to off-flavors he could taste but not explain. He started another. It failed differently. After three more years and a second restaurant near-failure on the strength of inconsistent fish sauce, he flew home for a week and watched his grandmother work, and he recorded everything she did. Not what she said — she didn't explain anything in words — what she did. The salt came in three layers, not two; she pressed with the heel of her hand, not her fist; she tilted the pot at fifteen degrees for the first day so the upper layer drained; she covered with a bamboo screen and a stone, not a lid; she put the pot in the corner that got morning sun and afternoon shade.

When he came back to Toronto, he started another crock. That one, his fourth, became the first one he sold. The crock now in the back of his restaurant is his nineteenth, give or take.

When Aroon started reading the modern food-microbiology literature on fish sauce — which he did in his late thirties, in a slow, self-taught way, after one of Danny's old culinary-school teachers passed him a paper — he had a strong and complicated reaction. The paper described the microbial succession of nước mắm fermentation in remarkable detail. It identified Tetragenococcus halophilus. It quantified glutamate concentrations at different ages. It described the volatile profile.

Aroon's reaction, as he later told Danny: all of this is right, and all of this was already known. His grandmother could not have told him about T. halophilus. But she knew that you wanted the second-year crocks for pad thai and the third-year crocks for pla rad prik (whole fried fish with sauce). She knew which fish from which boat in the Gulf of Thailand were best, and why. She knew when a crock was finished. She knew how to fix one that had gone wrong. The science had taken several centuries and a Western research apparatus to articulate what her household had known and practiced for as long as the recipes had been passed down.

This is theme #4 in its strongest form. Fermented fish sauce is not a niche food; in many parts of Asia, including Aroon's home, it is more central to daily flavor than salt itself. The science behind it has been catching up to the tradition, slowly, for the past century. The tradition does not need the science. The science is what we have, in our modern-research-paper-and-textbook way, of describing what generations of grandmothers already knew and did.

The taste at three years

A teaspoon of three-year nam pla, eaten on its own — which Aroon recommends nobody do, but which we will hypothetically do for the purposes of this case study — would deliver something like the following sensory experience.

First arrival: salt, immediately, but a salt that is layered. Behind the saltiness is the umami of high free-glutamate. There is a whisper of sweetness from the sweet amino acids (alanine, glycine). There is, very briefly, the trimethylamine top note that some describe as fishy, others as oceanic, and in this concentration is best described as a hint. The sourness is mild — the lactic acid contribution is not dominant, the sauce is pH 5.0 to 5.5, more savory than sour.

Mid-palate: depth. A long-roast-meat-broth depth that you don't get from short cooking. The same flavor architecture as a 24-hour pho stock. The same flavor architecture as a long-aged Parmigiano. The same flavor architecture, in fact, as the kombu dashi of a careful Japanese kitchen — because all of these are vehicles for the same family of free amino acids, in different combinations.

Finish: long. Way too long for a teaspoon. The savory-sweet length is what makes one drop in a stir-fry transform the dish. A drop. Aroon uses fish sauce in most of his savory dishes, sometimes a half-teaspoon for a four-portion plate, and the diner cannot tell the dish has fish sauce in it. They can only tell that something has happened to the dish that they cannot place. That is the right amount, Aroon says. If you can taste it, you used too much.

This is the principle of fish sauce, and the principle of every long-aged ferment: it is a flavor multiplier, not a flavor itself. The microbes have done years of patient protein chemistry on your behalf. Your job is to use the result wisely. A drop, into a dish that needs depth.

Analyze this

The microbial story of Aroon's three-year crock involves halophilic bacteria, slow proteolysis, and amino-acid liberation over years. The cultural story of the same crock involves a grandmother in Chiang Mai who could not have told you the microbial story but knew exactly what to do, and a grandson in Toronto who has taught himself both the doing and the explaining.

Several questions for you to think about:

1. Aroon's grandmother knew, by smell, when a fish sauce crock was finished. What sensory cues do you think she was responding to, and how would you describe them in scientific language? (Hint: think about what's accumulating, and what's no longer changing.)

2. Suppose a chef without Aroon's grandmother were to read the food-microbiology paper on T. halophilus and try to make fish sauce purely from the literature, with no exposure to a working tradition. List three things they would probably get wrong on the first try, and what role the tradition plays in keeping each of those right.

3. The chapter argues that "the science cannot improve on the tradition." Do you agree? Are there specific cases — in fish sauce, in any other ferment — where contemporary food science has identified something that improved or changed traditional practice? Cite an example if you can; speculate carefully if you can't.

4. The Roman Empire's garum was, by all archaeological accounts, a close cousin of nam pla. The Roman tradition died with the Empire's collapse, but the Asian fish-sauce traditions never broke. What does this contrast tell you about how food traditions survive (or don't), and what it takes to keep an applied-microbiology research program alive across generations without literacy?

5. Close to home: think about a cooking tradition in your own family, however small or local. Is there a step in that tradition that you have always done a certain way without knowing why? What might be the science behind it, and what would you lose if you started doing it "scientifically" instead?