DIY fermentation: confessions — and recipes — of a culture vulture

Like all the most dangerous habits, mine started with a youthful experiment: a funky Tunisian concoction called hrous, which comes from the edge of the Sahara. 

I was led to it by that peerless gastronomic explorer Paula Wolfert and her Mediterranean Cooking, a take-you-there book that was published in 1977, a year when toothpicks were still commonly used to impale pineapple and cheese.

Her recipe was for an earthy onion-chilli paste, churned with spices and rosebuds, which has a depth of flavour that can lift any soup or stew. But what hooked me was the traditional Gabès method for making the stuff.

“In the typical southern Tunisian home,” she wrote, “the cook will slice around seventy pounds of fresh onions, toss them with salt and turmeric, pack them in earthen jugs, and leave them for three months to become soft and wet.”

Wolfert’s version of hrous was simplified and shortened for convenience. But the long Tunisian path proved irresistible to me. When I finally popped open the lid on the onion jar, stashed in a cupboard, the ripe pong was admittedly something best kept away from anyone you might be hoping to feed. But the finished paste was sensational. 

From then on, nothing quite satisfied me like spiking food with time and microbes.

In periods of stress in particular, I would attempt ever more inexplicable things. When Brexit negotiations were at their peak in Brussels, I’d return from reporting on summits in the early hours and tend my crop of koji, the sweet-smelling wonder-fungus behind soy sauce and miso. 

Lockdown really hastened my slide. It wasn’t just sourdough for me. My cupboards were used to brew butternut squash vinegar (using Polish moonshine and an air pump commonly found in aquariums), maple syrup drinks given a tart bite by kefir water crystals and a form of miso made with yellow peas (I can tell you how it tastes in September).

The search for an umami high eventually left me trying to recreate a Noma restaurant classic, standing over a sludgy jar full of insects — crickets and wax moth larvae — that I was going to cook at 60C. For three months.

These days, I cut my hrous with Turkish aci biber salcasi, or hot pepper paste, which counts as another miracle of the long wait. My batch comes from an old family supplier in the south-eastern province of Hatay, near the border with Syria, where I would visit my grandparents as a child.

There is something impossibly eccentric about entrusting microbes to make things taste good

Trimmed and deseeded, the red peppers are pushed through a mincer and tossed with salt, leaving a juicy pulp that is traditionally left out to dry in the sun. You can find apartment blocks in this region with vast paddling pools of chilli on their roofs, open to the sun and night air. Usually it takes about a week to reach perfection.

This is one of the cooking staples I do not even bother to attempt myself. I could never recreate the maturity of the flavour, a warming glow that creeps up on the back of your mouth, unlike regular hot sauces that crackle across your lips and tongue.

Biber salcasi made the proper way is only lightly fermented but it still belongs to a family of foods — such as kimchi, kefir and kombucha — that rely on bacteria, fungus or enzymes to work magic. Some devotees rave about their probiotic benefits. Others approach them with laboratory-style rigour. Whole papers are written about the science of latter-day garums, which the Romans pioneered by dumping old fish heads into big clay pots and waiting for them to give up a sublime juice.

My motivation is different. These experiments are often delicious, occasionally foul, but always entertaining. There is something impossibly eccentric about entrusting microbes to make things taste good. And when the world shut down, I took out my frustration on some unsuspecting insects.

My path to that dark place, and grasshopper garum, followed The Noma Guide to Fermentation. It is a remarkable book offering a glimpse into how this Danish restaurant became known as one of the finest and most daring in the world.

On page 44 are instructions for “Building a Fermentation Chamber with a Covered Speed Rack”. The assembly procedure includes sourcing a two-foot wheely-thing (the type you’d see holding used trays in a canteen), a space heater, humidifier, hygrometer and wraparound plastic cover. The extra wool blanket is optional.

There are, thankfully, simpler ways. My ever-understanding wife bought me a Brod & Taylor proofer and slow cooker, which allowed me to cultivate koji and stew my first beef garum. That recipe involves blending a kilogramme of mince with pearl barley koji, salt and water, before packing it in a jar and leaving it to cook at 60C for about 12 weeks.

The strained result is a dark, unctuous blast of savoury flavour — something like a beefy soy sauce. Noma’s René Redzepi and David Zilber use it in a fabulous pasta dressing, mixing it with egg yolks and Parmesan. Yet this garum gives complexity and depth to virtually any meat or vegetable dish. I’ve even used it as a light savoury glaze for sweet buns.

There is nothing more highly prized at Noma than the grasshopper garum. This long, sophisticated, chocolatey potion is so versatile and so good they had to stop it popping up in too many of their dishes.

Noma suggests using live grasshoppers as well as wax worm larvae, little cream-coloured wrigglers that definitely look better as moths. Sourcing initially looked simple but, in the required quantities, it turned out to be a Google-defying mission (one example from my search history: “Are pet shop grasshoppers safe for human consumption?”).

There is nothing more highly prized at Noma than the grasshopper garum, it is so versatile and good

I didn’t relish seeing the little critters jumping around in my food processor either. My squeamish compromise was cricket flour, a high-protein powder, which I am told makes a mean chocolate brownie and is catching on fast among insect eaters. I won’t go into the details of my encounter with 300 gram of wax worms, but let me just say that, when working in bulk, the sawdust is hard to separate from the larvae.

Believe me, the finished product was good enough to do it all again. But even failures carry a certain satisfaction. This fermenting business needs an intrepid spirit and a sense of humour. As the Noma team put it: “There is a thin line between rot and fermentation.”

Hrous with a Turkish twist

1. Using your hands, mix the onions with the salt and turmeric. Pack tightly into a large glass jar. Cover the surface of the onions in the jar with a layer of cling film, which should run a little way up the sides of the glass. This reduces exposure to the air and unwanted bacteria. You can use a Ziploc bag to weigh down the onions so (eventually) they stay submerged under their own juice. Do this by pushing the empty bag into the remaining space in the jar, fill with water, then seal the bag.

2. Don’t seal the lid of the jar — gasses should be allowed to escape. Cover the opening of the jar with muslin and secure with a rubber band. Leave for three months at room temperature. Check occasionally to make sure onions are submerged.

3. Squeeze the onions dry using a muslin cloth.

4. Add the aci biber salcasi or dried Aleppo pepper to a food processor, along with the spices and the onions. Add oil while you blend. Put into a jar. Cover with olive oil. Keep refrigerated.

Pomegranate and maple water kefir

This refreshing drink is a great companion on a summer afternoon. Water kefir crystals, or tibicos, can easily be found from suppliers online. It has a much lighter flavour than kombucha. Compared to a kombucha culture, the squidgy, translucent kefir crystals are far less ugly too. You can play around with all sorts of flavours at the second stage of fermentation — other fruit juices, slices of ginger, a cinnamon stick or just another dollop of maple syrup.

1. Use a large, clean glass jar with a lid. Add the kefir water crystals, maple syrup and filtered water.

2. Leave at room temperature for a day or two. Bubbles should appear, a sign that the crystals are eating up the sugar. Stop when the water is starting to sour, but still has a hint of sweetness. At one point the water can seem flavourless — that’s the turning point. Wait it out.

3. Strain the water into glass bottles and leave an inch or two of space (the crystals are ready for use in another batch). Lightly crush the pomegranate seeds, then add to the bottle along with the juice.

4. Leave to ferment at room temperature for a day or two. The longer the drink is left, the more carbonated and sour it will become. When ready, “burp” the contents and refrigerate. Watch out for exploding bottles.

Alex Barker is the FT’s global media editor

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