Garums, misos and lacto-ferments can be a way to upgrade almost anything a kitchen would normally throw away. Ryan Walker of Silo explains the process to Maria Mellor
There's a tray of wild rabbit carcasses in the back kitchen of Silo in London's Hackney. What sinewy meat is left on the bones is minimal – even the offal has been carved out to be served as a filler for dumplings – and there's not enough gelatine in the rabbit bones to make a useful stock.
However, Ryan Walker is unperturbed. He takes a cleaver and, with mighty chops, divides the carcass into three-inch sections and chucks it in trays to be roasted. But what he's making isn't some sad Victorian excuse for a staff meal, it's part of his way of upcycling ingredients as the restaurant's head of fermentation and research and development.
"Upcycling is essentially taking something and making it a better form of itself," explains Walker. "You're taking a ‘useless' thing that is always discarded and turning it into something with loads of value." The wild rabbits will be turned into garum – a soy sauce-like liquid that can be used to impart salt and umami to a dish. Almost anything with protein can be turned into a garum; in Silo's store cupboards velvet crab, venison and Parmesan rinds can be found fermenting, with the clear favourite, labelled "liquid gold", made from egg whites.
"Unless you're making 100kg of meringues a month, we find garum to be a better, less wasteful use of egg whites within our system", says Walker. "You'll be stood in the walk-in fridge, taking a look around and you'll see ‘oh we have loads of egg whites', or ‘there's quite a lot of this trimming'."
He describes the taste of garum as similar to fish sauce but without the intensive smell and dietary restriction. Walker was promoted to his current role having worked his way up from chef de partie at Silo, and his job is to divert what little food waste the restaurant produces into useful ingredients.
He upcycles food waste in three main ways: as a powder after putting it through the dehydrator, by lacto-fermenting it, such as with kimchis, pickles and sauerkrauts, or with koji, a fungus used in the production of sake, mirin and miso. As dehydrating can have a high energy cost and lacto-ferments can be on the more volatile side (a jar of lacto-fermented piquillo peppers recently exploded on Walker as he tried to tidy up the fermentation cupboard), koji is Silo's main focus.
The raw materials to ferment protein
The packet containing the koji spores is packaged in plastic – an incredible rarity for the sustainably minded Silo – but the spores themselves are so tiny they need careful management. A little goes a long way. Just 0.1g will inoculate 1kg of rice koji, creating up to 3kg of garum.
The rice itself is from France and some of the most sustainable the team can source. This not only means they receive the rice via sail cargo, but that it adheres to the PGI Camargue rice specification – a guarantee of sustainable farming. France also funds and conducts research on growing sustainable rice worldwide.
Experimentation is a huge part of Walker's role at Silo. In the aforementioned store cupboards sits a huge 60-litre vat labelled ‘fight club fish sauce' – "because we don't talk about it," explains Walker. A tuna carcass was due to be thrown away by sellers at the market, and rather than witness the binning of this already unsustainable fish that they'd never usually consider for Silo, they took it into their own hands. The idea was to create fish sauce, but a hurdle revealed itself when the key enzymes in the fish viscera were found to be inactive. Walker added koji and restarted the process.
A torch shone into the opaque walls of the vat reveals a dark mass at the top and bottom – fat and koji – with liquid in the middle. Walker looks at the vat fearfully, having sampled the incredibly (and unusably) pungent sauce.
"It's almost three years old and I feel it needs even longer to mellow out," he says.
For now they'll stick to the egg white garum.
From waste oranges to creative kefir
And that's not the only interesting project on the go – the team were also given a crate of oranges stripped of their zest for use in mulled wine. Though he says the zest is usually the best bit of the orange, Walker sets to work on the flesh and juice. The pulp is mixed with 2% of its weight in salt and 10% koji into the hope of creating a masterpiece to put on menus at a later date. The juice is used to make kefir, which can then be reduced and emulsified with butter to create a rich and acidic sauce.
"I've never seen a sauce like it," says Walker. "We were using whey before, but discovered you could do the same thing with kefir."
Walker is keen for other restaurants to start their own fermentation journeys. Though some might already be experimenting with flavours in small doses, he feels more could start diverting food waste into their fermentation projects. He enjoys using ferments in interesting applications, such as what the team calls "garumel" – a mix of garum and caramel to be used in desserts for a sweet-umami flavour. Silo doesn't have any specialist equipment to be able to ferment in large quantities – all it takes is a stack of muslins, some steamer trays and two Rational combi steam ovens.
"If we can do it, anyone can," says Walker. "There's been a lot of fine-tuning and trial and error, but there's no reason why any restaurant who has access to these bits of equipment can't attempt it."
Mushroom miso on maitake mushroom
Maitake mushrooms are a fragile fungus so there is some breakage before they arrive at the Silo kitchen. Of course, it would be against the restaurant's strong morals to refuse them, so the broken bits are placed in the hands of Walker. He combines them with an equal quantity of shiitake mushrooms and creates a miso by partially dehydrating them while smoking over birch then combining with salt, rice koji and dashi. This miso is brushed on top of the original maitake mushrooms while they are being cooked.
Rabbit head garum
- 1,200g rabbit heads
- 500g rabbit offal
- 1,900g kombu dashi
- 2,000g rice koji
- 672g salt
Roast the rabbit heads at 175°C for 45 minutes or until very dark in colour and caramelised. Cool the rabbit heads to 60°C and combine with raw fresh rabbit offal, koji, salt and dashi in a large container and mix well.
Ferment at room temperature for nine months, stirring every day for a month, then every other day until ready.
Finish at 60°C for two weeks and then leave in the fridge for another two weeks to settle.
