The problem with the science of diet is that if you’re only partially interested, gobbets of information go in and stick, surrounded by great gaps that you fill by whistling and not quite caring. So, I know that the microbial environment of the gut is crucial to good health and longevity. And that fermentation is vital to the gut, though I didn’t realise how vital until I spoke to Tim Spector, professor of genetics and author of The Diet Myth. It’s part of a suite of things that are good for you, along with “low-salt” and “very green”. “The complexity of adding fermentation to any food, as well as adding 10 times more flavour, releases more chemicals into the food; and the more chemicals there are, the more likely they are to be helpful to the body.”

The process works differently depending on the food type, but there are a few key principles; you can’t just pickle, you have to pickle in brine, not vinegar, because acid kills everything. The English were left behind by fermentation, having prematurely fallen in love with vinegar, which is why we’re not as hardy as the Hungarians. Problematically, if you like your health awareness with a side order of self-flagellation, fermentation is quite delicious.

Flat Three is a Swedish/Japanese fusion restaurant in London where they ferment in-house and pair their pickles with fermented juices, though you can have wine, if you like, because that’s also fermented. Miso looms large, but the flavour bomb is meju, a fermented bean paste to which you can add brine to turn it into doenjang, or fermentation squared. Something incredible happens to celery and cabbage pickled in brine: the intensity of flavour is like a dream, or the beginning of a stroke.

Kombucha, the black tea, is brewed from a live culture called a scoby; Merlin (of course the restaurant guy’s called Merlin) has a culture at home that was his grandmother’s (though we may have been talking about a yoghurt by then; something in the ineffable proliferation of the microbes makes it hard to track which superfood you’re on). “Did you get the scoby?” Spector asks. “I bought a kombucha in Hackney at the weekend [of course it was in Hackney], and it had this little blob of microbes and fungi, all living together, at the bottom.”

That living community will react with your own microbes to produce something new. But they’ve recently found that the microbes don’t even have to be alive: chocolate and sourdough both undergo fermentation, which is long dead by the time you eat it, but they’re still good for you, because the process has started breaking down the food before you try to digest it.

“We can’t prove it yet,” Spector says, “but there’s a theory that even dead microbes can have a signalling effect, that makes your own microbes want to copy them.” I started to think of my gut as like a 1990s rave, the mad vivacity of partially intelligent life forms all mimicking each other. It’s a strangely hedonic health kick.

What I learned

A British Gut survey of 3,000 people found there is not much to choose between vegetarians and non-vegetarians, but there is a clear difference between people who eat a varied diet and those who don’t