How fermentation works its magic at Borough Market
Words: Clare Finney
A simple stroll round Borough Market will bring you up against hundreds of different products that have bacterial action at their core, and there isn’t a civilisation in the world that doesn’t use fermentation in one form or another. So, what is fermentation and what are the various ways in which it works?
Put simply—by the Oxford English Dictionary—fermentation is “the chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, typically involving effervescence and the giving off of heat”. Such microorganisms are everywhere—in the air, on our skin, our fruit, our milk, our cereals, our vegetables—and there’s a lot of good and bad they can do. Fermentation involves encouraging the good ones—often deliberately adding them through a starter culture—while removing the ability of pathogenic microbes to flourish. Lactobacillus, one of the main types of bacteria used in culinary fermentation, produces lactic acid as a by-product of digestion, creating an acidic environment that proves inhospitable to pathogens while also producing the distinctive tang found in many fermented foods.
Different bacteria, yeasts and enzymes will be used in the fermentation of different foodstuffs. Lactobacillus bacteria are key agents in the production of kimchi and sauerkraut and are also prominent in the starter culture used to make sourdough bread. When flour is mixed with water, enzymes contained within it split starch into sugars. Naturally occurring lactobacilli convert the sugars into lactic acid, causing unwanted bacteria to die—at which point the yeasts in the starter that tolerate acid come into their own. These yeasts convert the remaining sugars into ethanol and carbon dioxide, so the starter starts bubbling merrily. This is what leavens the bread dough and gives it its fruity, sour taste.
A source of pride
“It’s magic,” says Olivier of Olivier’s Bakery, whose starter is a source of great pride. “Flour has a terrible taste on its own, but it develops its own rich flavour and aroma when you process it with salt, water and time. It can be nutty. It can be chewy and you can create all this with basically nothing.” It’s not easy, he continues: “Every week we receive a different batch of flour, every week the weather changes, so we’re constantly adjusting the amount of time and water, but the beauty of it is that you can’t cut corners.” Even in a city in which we can barely stop to catch our breath, fermentation demands time.
Of course, it’s impossible to talk about fermentation and Borough Market without talking about cheese: a tangible, tasty reminder of just what these invisible organisms can do. “There are billions of bacteria in each cheese. They are living things,” says Bath Soft Cheese’s owner Hugh Padfield.
Bill Oglethorpe of Kappacasein adds his own starter culture to the bacteria that live naturally in raw milk. “There is lactic acid bacteria—the bacteria needed to convert lactose into lactic acid—in raw milk anyway. The starter boosts the already naturally occurring microorganisms,” he says. Bill makes his starter by incubating milk overnight, testing it for good lacto-fermentation, then—if impressed—putting it into fresh milk. “The process is a closed loop: we put 50ml into a litre of fresh milk, leave it for eight hours, take 50ml out and put it in the fridge. The following week we take that 50ml, put it in a litre of fresh milk for eight hours, take 50ml out, put it in the fridge and so on.”
Texture, depth and complexity
Before driving it back to London from the dairy in Kent, Bill adds his starter culture to the fresh milk so that the fermentation process kicks in even before the cheesemaking officially begins. He uses this milk to make all his cheeses, as well as his natural yoghurt, which is fermented again after it has been boiled. The result is a yoghurt with a texture, depth and complexity that’s a far cry from the supermarket or even deli-bought equivalent—a rich, creamy, slightly tart reminder of the difference expertly managed fermentation can make.
As a cheese ages, the busy microorganisms work to degrade the casein proteins of the milk, first producing medium-sized peptides, then smaller amino acids. These amino acids not only contribute towards that basic cheesy flavour but serve as precursors to the volatile aroma compounds responsible for the more specific smells and flavours of different cheeses. Fats, too, can be broken down by bacteria, producing other tiny molecules that affect the taste and texture of the finished product.
This ancient process applies to all cheeses bar those that, like ricotta, are acid coagulated. What enables their rich variety in appearance, texture and flavour is a whole range of factors: the strains of bacteria in the starter culture (and, in the case of unpasteurised cheeses, in the milk itself) and in the atmosphere; the treatment of the cheese through rind washing, turning or piercing; and the location, time and temperature at which it is matured.
Earthy, funky flavours
The way in which fermentation by lactic acid bacteria can result in earthy, funky flavours is also put to good use by charcuterie makers who produce the kind of dried, spiced sausage known broadly as salami or saucisson—lactic acid creates an inhospitable environment for pathogenic bacteria and imparts the chewy texture and earthy flavours essential to salami’s appeal.
Less obvious beneficiaries of bacterial alchemy include coffee and chocolate (tea is commonly referred to as being fermented, but it is oxidised, which is not the same thing). Not all coffee cherries are fermented—some are dried in the sun—but the fermentation method, or ‘washed method’, lends the resulting beans a lively brightness of flavour. One such coffee is the yellow caturra—a rare variety of arabica named for its unusually yellow (rather than red) cherries—which is carefully sourced by Eduardo Florez at The Colombian Coffee Company.
The cherries are picked only when they are perfectly ripe. “They are then passed through a machine to remove the skin, before being left in water for anything between 20 hours to a day and a half, so that the pulp naturally ferments. The bad cherries—those that have been eaten by a bird, for example, or are not perfectly ripe—will float to the top and are removed,” says Eduardo. “This process is continued until each remaining bean is perfect.”
Complexity and depth
In coffee, fermentation describes the action of yeasts and bacteria on the sugars in the mucilage of the coffee bean (the gelatinous layer covering the seed after it’s been pulped). This produces acids, which add complexity and depth to a coffee. The fermentation of chocolate follows a similar pattern, in that it is not the beans per se that are fermented, but the pulp surrounding them. At Rabot 1745’s estate in St Lucia, the cacao pods are harvested by hand, broken open once they reach the processing area, and their contents—cocoa beans wrapped in a slimy sweet mucilage—are deposited into a fermentation bucket covered in palm leaves for seven days until the beans begin to turn pink. Only once the fermented beans are sun-dried, sorted by hand, and roasted are they shipped back to the UK to be ground into cacao nibs, and it’s these nibs that make chocolate.
Over at Eaten Alive, Pat and Glyn are using the ancient technique of fermentation as a boon for culinary creation at their pickle stall. Before setting up, they were partly inspired by the wisdom of Sandor Katz: a man whose book, The Art of Fermentation, is popularly considered to be the bible of bacterial action. Listening to Pat and Glyn expound on Katz’s virtues brings to mind something that Katz himself said in a recent NPR podcast interview, which sums it all up perfectly: “We reject certain food because it is rotten. Certain food we can see is fresh. But there is this creative space between fresh food and rotten food where most of human culture’s most prized delicacies and culinary achievements exist.”