NEW YORK » Say this about Sandor Ellix Katz: the man knows how to get you revved up to eat bacteria.

"Oh, this is nice kimchi," he said on a summer afternoon at Momofuku Noodle Bar, using chopsticks to pull crimson-coated knuckles of Napa cabbage from a jar. "I like the texture of the sauce. It’s kind of thick."

Kimchi, like sauerkraut, is one of the world’s great fermented foods, and Katz, a resident of Tennessee, was curious to see what David Chang’s team of cooks in the East Village would do with it. Lately Katz has become for fermentation what Timothy Leary was for psychedelic drugs: a charismatic, consciousness-raising thinker and advocate who wants people to see the world in a new way.

A fermented food is one whose taste and texture have been transformed by the introduction of beneficial bacteria or fungi. And Katz, who turned 50 this year, considers it a big part of his mission to remind us that the tangy delights of that metamorphosis surround us — and always have, if you look back at the arc of human evolution.

"I don’t believe there’s a restaurant in the world that doesn’t have products of fermentation on their menu," Katz said. "If you have bread, you have fermented food. If you have cheese, you have fermented food. If you have salad dressing or anything with vinegar in it, you have fermented food. If you have alcoholic beverages, you have fermented food. I mean, you really can’t get through the day without eating something fermented."

Nevertheless Katz, whose latest book, "The Art of Fermentation" (Chelsea Green), recently went into its third printing, maintains a special fondness for the funkiest manifestations from around the world. "When I walk into a restaurant, I peruse the menu to see if they have any special ferments," he said.

He was in luck at Momofuku, where the crew, led by Chang, prides itself on exploring new microbial pathways. Tim Dailey, a sous-chef at the Noodle Bar, brought Katz a glass of an amber-hued German-style helles beer that he had brewed (and that is not regularly served at the restaurant). There were pickles, too, and an egg marinated in soy sauce; a summer-squash salad that had been laced with white kimchi (that is, a kimchi without the usual spicy creek of red chile pepper running through it); and an assortment of warm fungi arrayed upon a pool of black-garlic yogurt.

"Oh wow, what’s that?" Katz asked when that last dish arrived.

"It’s a mushroom salad," Dailey said.

To share a meal with Katz is to be reminded that you are sharing it with a vast army of invisible dining companions. As he dug into the mushrooms and yogurt, he talked about a recent study, the Human Microbiome Project, that has deepened the understanding of how our bodies are occupied by "trillions of bacteria," most of which appear to be committed to the noble enterprise of keeping us healthy and functioning. Katz believes that fermented foods help replenish a diverse variety of probiotic bacteria in our guts, and his interest in the topic can be traced back to a health crisis of his own. In 1991, while working in New York City politics, he learned that he had contracted HIV.

Suddenly unsure of how many healthy years he had left, but certain that he didn’t want to squander them trudging through stress-throttled 80-hour workweeks, he moved to a rural commune in Tennessee. "I didn’t have experience as a gardener, but that was something I was interested in pursuing when I got there," he said. "I felt myself called by plants."

Blame bumper crops of cabbage for his fermentation fixation: Since he had to do something with the cabbage before it rotted, he soon found himself making sauerkraut, and learning more and more about its health benefits and the role that preserved vegetables had played in the course of civilization.

"Agriculture doesn’t make sense without ways of storing the harvest," he said. "Stuff happens when you try to store food, or inadvertently let food sit around. Just as our bodies are covered with microorganisms, everything we eat is covered with microorganisms." (Still, Katz often stresses that fermented food hasn’t "cured" him of HIV, although he does think it’s possible that friendly bacteria have helped reduce some side effects of the medications he takes.) If, as books by other authors have argued, cod changed the world and the Irish saved civilization, Katz’s work often brushes up against the idea that the discovery of fermentation provided a crucial step in human evolution. We ate, we drank, we changed.

"It seems likely that our primate ancestors were familiar with fermenting berries and were even familiar with the phenomenon of inebriation," he said. Human beings "figured out how to liquefy the berries and make beverages," spurring the development of both pottery and poetry.

There’s no denying that fermentation has drastically expanded the spectrum of what’s available to the human palate. "Ferments are huge sources of flavor complexity," Katz said. "That’s why people find cheese so compelling. That’s why soy sauce has become a universally loved condiment."

At home, Katz devotes much of his days to flavor experiments. "This woman in North Carolina taught me that Cherokee people used to take their excess corn and pickle it in a brine, and it’s incredibly delicious like that," he said. "I’ve been doing a variation on that where I cut kernels off the corn and make like a fermented corn relish. I ferment it just for a few days in a jar and it gets this beautiful, sharp flavor."

Pungent tastes and aromas don’t dissuade him. A while back he tried his hand at making balao-balao, a Filipino specialty in which rice is fermented with shrimp. "I loved it, and as the days passed and the flavors got stronger, I liked it more and more," he said. "I brought it to a potluck meal that some friends had organized. And as I reheated it, I noticed that it got really, really smelly. A year later my friends are still telling stories about that crazy smelly fish that I tried to serve them."

Naturally, a seeker like Katz couldn’t resist an invitation to visit Momofuku’s laboratory of fermentation, so after lunch he took a short stroll to an unmarked sliver of office space in the East Village, where he met Dan Felder, the 28-year-old head of R&D for Chang’s network of restaurants.

There, in the Momofuku test kitchen, Felder gave Katz a glimpse of a brilliantly demented-fermented future: Erlenmeyer flasks full of new iterations of soy sauce, jars of vinegar conjured up from ingredients like strawberries and cherries, little mounds of paste that represented the next wave in miso. There were vials of explosively flavored tamari, a mere droplet of which might garnish an oyster.

"It’s basically, ‘How do we make umami from scratch?"’ Felder explained.

As with molecular gastronomy and the farm-to-table movement in the past, a deep focus on fermentation can help a chef like David Chang (or Rene Redzepi at Noma in Copenhagen, Denmark) stake out fresh territory for creative expression. Every time the Momofuku crew hatches a new flavor, Felder said, "the more expansive our repertoire can become."

To demonstrate this, he reached into a fridge and removed some laces of creamy fatback dusted with salt and a mold-colonized barley used to make products like soy sauce and miso.

"Koji-cured lardo," Felder said. "This is a new frontier."

Katz reacted to the lardo and everything else like a kid in a kimchi shop, even going into a brief reverie when a jar of Basmati koji was opened and his nasal passages got to bask in the fragrance. "Oh, my God, what a beautiful aroma," he said. "It’s a gorgeous mold. I am so in love with koji."

Traditionally, miso has come from fusing that mold with rice or barley, then adding it to a base of soybeans. But Felder brought out several versions that had been made, instead, with ingredients like pistachios, pine nuts, lentils or mung beans.

"I’m fascinated by this idea of nut-based misos," Katz said. "I want to taste them all, really. The pine nut was amazing."

"That’s Chang’s favorite," Felder said. "You get this incredibly creamy mouthful."

Katz swooned over the pistachio miso, too ("Oh, my God, this is so delicious"), and as he prepared to leave, his blue eyes were brightly shining.

"It’s really exciting for me to see these crazy new applications," he said. "I feel like this is going to influence my experimentation."

© 2012 The New York Times Company