Standing in the middle of an old cathedral hall in Westminster, there's something that sticks out immediately as I walk in. It's not the fact that the room's chock full of tables which themselves are covered in loaves of bread – I'm here to help judge the World Bread Awards, so it would be a surprise if that weren't the case – but the fact that of the hundred-plus loaves that are here to be judged by me and 25 or so other people from various sectors of the food and drink industry, the vast majority have the unmistakably knobbly, rugged look of a freshly baked sourdough loaf.

Sourdough loaves at the World Bread Awards judging

Sourdough loaves at the World Bread Awards judging

Currently, the UK is riding the crest of a (delicious) sourdough wave. No doubt, when you scan your brunch menu at midday on a Saturday, choosing which dish is going to take the edge off your hangover in just the right way, the majority of options will be served on sourdough toast. Bakeries all over the city are putting out sourdough loaves in their dozens: the round shape, darkish colour and trademark 'ear' – the little crusts that form where the dough's been scored – are all dead giveaways. And, inevitably, supermarkets are getting in on the action, selling sourdough pre-sliced in plastic packets.

Only it's not. While that bread might taste 'sour', these new-school variants aren't true sourdough loaves. The key to sourdough is natural fermentation – the process of yeast that occurs naturally in the air (or a culture created from this, which is 'fed' continually with flour and water, known as a 'mother') being added to dough to start fermentation. Essentially, if you add yeast – even traditional baker's yeast – you're cheating a centuries-old system of making leavened bread naturally.

"In the last couple of weeks, two of the biggest industrial loaf fabricators in the country have released wrapped, sliced loaves that they're calling sourdough," says Chris Young, whom I see at the Awards and follow up with a couple of weeks later, "but they're full of artificial additives – we don't think they should even be called bread, for a start – but more to the point on the sourdough issue, they're made with added yeast."

if you add yeast – even traditional baker's yeast – you're cheating a centuries-old system of making bread

Young is right. And he should know: as the coordinator of the Real Bread Campaign, an offshoot of food and agriculture-based charity Sustain, he's been flying the flag for real baking since 2008, when he joined. "I went on a course with a guy called Andrew Whitley," he says, "and as part of that he highlighted some of the issues there are with our daily loaf, following on from his book, Bread Matters. By the end of the week, I was one of the people going 'Oh my god, I didn't realise they were doing that to my loaf. What can I do to help?'"

Young quit his job later, and his job ever since has been to knit together the community of bakers in the UK and get consumers more knowledgeable about the benefits of proper bread. The campaign created a sourdough-specific initiative later: "We created Sourdough September in 2013. It followed on from Real Bread Week in 2010, which was a celebration of real bread – aka additive-free bread – and the people who make it, encouraging people to buy loaves from small, independent bakeries, or to bake their own at home. Then, in 2013, we then went a bit more specific – exactly the same ideas and aims, but with sourdough."

It's a view shared by Fergus Jackson, who set up South East London's Brick House bakery with his wife Sharmin in 2012 after baking in his spare time became "a hobby that was getting a bit out of control. "I first came across proper sourdough from St John Bread & Wine's bakery," Jackson continues. "I worked a few doors down and I used to go in there and buy bread. I got to thinking 'This is how good bread can be.' I may have eaten sourdough before, unknowingly, but this was the first time it made a real impression on me."

Fergus Jackson, co-owner of Brick House Bakery in East Dulwich and Peckham

Fergus Jackson, co-owner of Brick House Bakery in East Dulwich and Peckham

Jackson then attended the vaunted San Francisco Baking Institute, which specialises in sourdough baking, and his imagination was totally captured by the process. He opened Brick House after a stint working for Hackney's E5 Bakehouse, and has since grown Brick House into an East Dulwich bakery with a smaller offshoot in Peckham. "I think the really interesting thing is that it is just flour, water and salt," Jackson says. "You don't add anything else to it – you develop and ferment your culture – but that's the purest definition of alchemy; turning these raw ingredients into something else. It's a totally natural process. It's a really interesting transformation, and there's so much on a biological level that's going on within it to make it happen."

If the tables groaning with hunks of sourdough at the World Bread Awards are anything to go by, there are a lot bakers hooked on this style of baking. In fact, late last year, the iconic Food Hall at Harrods reopened to the public, featuring (among plenty of other things) a huge, sourdough-only bakery. That's not just loaves fit for taking a bread knife to and toasting; it's baguettes, rolls and pretty much everything else you can think of, too. Sourdough, after all, is a style of baking, not necessarily just a type of bread. A company as big as that dedicating a huge site to this type of baking is as much of an indication as the supermarkets' knock-offs as to its popularity.

that's the purest definition of alchemy; turning these raw ingredients into something else

I get the chance to try out some sourdough baking for myself, at Brick House's East Dulwich location on a weekday evening. Jackson teaches the class to mix dough with levain – essentially a large piece of 'mother' culture mixed with a little dough, which kicks off the fermentation process – and return to it half an hour later to see it balloon in size as the natural culture gets to work on the gluten particles in the bread. It takes some turning, in reasonably precise intervals, before it's turned over, kneaded, shaped, scored, and put in a steam oven to cook. It comes out a while later richly aromatic, beautifully imperfect, and, of course, delicious. The air pockets created by the air let in during fermentation are a feast for the nose as well as the mouth. And the texture – elastic and tactile but beautifully natural-feeling – is a taste of what's to come when I eat it.

Brick House Bakery in East Dulwich

Another thing: many experts believe that sourdough baking has not only a stylistic benefit and a better flavour, but that it has health benefits, too. Natural fermentation, they claim, helps break down the stretchy gluten particles that cause a significant percentage of the population problems with digestion – as opposed to the rigid gluten present in industrialised, mass-produced bread made to rise super-fast with artificial yeast and other additives.

"Gluten is basically two proteins," says the food writer and documentarian Michael Pollan narrates in the excellent Netflix show Cooked. "And when you moisten flour, these two proteins, they kind of mesh together. And when they do, they form a substance that's very stretchy, extensible, but it also will return like a balloon." The rise of people reporting gluten intolerance (a more subjective, less medical definition than something like coeliac disease), he argues, may be more down to the way we've industrialised bread production in the last few decades. After all, "the bread you buy in the supermarket," he says, "is very different than what bread was for most of history."

Which is why, according to bakers like Jackson and campaigners like Young, the fact that the forces responsible for industrialising bread production are now latching on to the popularity of sourdough. "I think it's still thought of as an elitist product, because it's much more expensive than your average supermarket loaf," says Jackson. "The kind of people who can afford to buy sourdough are the kind of people who are more connected to their ingredients anyway. That's almost an unfortunate state of affairs, because the supermarkets and the people who are out to mass-produce stuff can make this product, albeit a counterfeit version of it, and then distribute it to places where a lot more people shop."

It's a problem of identification, because even if the message about the health benefits of sourdough get through, it's moot if what people are buying isn't what it seems. "As soon as you add yeast, you speed up the process, and it means that all the funky alchemy you get with proper sourdough bread hasn't got enough time to do that stuff," says Young. "Time is an essential ingredient in sourdough bread, and if you cut that out, it just isn't sourdough bread anymore.

"Any potential benefits – whether that's flavour, aroma, or potential health benefits – there's just not the time for those to be fully expressed. Or they don't even happen at all." So what's the solution? The popularity of sourdough bread is only increasing, and so is the appearance of what the traditional baking industry sometimes refers to as 'sourfaux' on supermarket shelves. "The Real Bread Campaign's having meetings with Defra and writing to politicians, and we've been calling for years now for what we call an Honest Crust Act," reports Young. "That would require that all bakers have to put full ingredients lists, including any additives they use, on display for all loaves, including those that are sold unwrapped. The other thing is legal definitions of words including sourdough, freshly baked, wholegrain, artisan bread and a few others."

Back at the World Bread Awards, the best loaves among the ones I judge – and the one we put forward as the best on our table, to be entered as a potential outright winner (still unannounced at the time of writing) – are sourdough, with that trademark tang, aroma and texture that, as hard as the industrialised food industry tries, is impossible to create artificially. As for the consumer? Until what Young's proposing actually happens and companies are held to account for what goes into their bread, it's up to to individuals to be savvy, and the best way to do this is probably to shop at independent bakeries who can tell you exactly what they put into the bread they make – with tools like the Real Bread Finder on the Real Bread Campaign's website a good place to start.

The crucial thing to note is that if it's sold as sourdough, that should be nothing but "flour, water, and a bit of salt," as Pollan and Jackson both describe it. And time, of course: for a product as beautiful, alchemic and natural as a proper sourdough loaf, a little time is more than it deserves.