A sourdough loaf can cost up to £4 in a bakery but a fraction of this price in the supermarket. Our research shows they're not necessarily the same thing.
Traditional sourdough contains only four ingredients: flour, water, salt and what's known as a starter culture.
A starter culture is made from flour and water and contains lactic acid bacteria and naturally occurring yeasts. This starter is developed into a dough by adding flour, water and salt over hours and days before baking. It takes between one and three days to make a traditional sourdough loaf.
But 'sourdough' is not a protected term, which means that, as Chris Young from The Real Bread Campaign told us: 'there's nothing to stop manufacturers using that word to market products that are what we call sourfaux'.
Many supermarket sourdough loaves we investigated contained additional ingredients that make it possible to complete a loaf in a couple of hours, making it cheaper to produce.
While these ingredients aren't bad for you, or unhealthy, they are not present in traditional sourdough bread. And if you're someone who chooses sourdough because it doesn't contain added yeast, you'll want to avoid those loaves that contain it.
It's not always easy to tell how authentic your loaf is, though. Most supermarkets list their sourdough loaf ingredients online, but Asda and Morrisons didn't during the period of our investigation. The ingredients weren't available at bakery counters in store, either.
Of the 19 supermarket and branded loaves we looked at, only four got the stamp of approval for authenticity from The Real Bread Campaign. These were:
Our advice is to check the ingredients and if you're looking for an traditional loaf avoid those containing yeast, yoghurt and vinegar. If ingredients information isn't provided, ask in-store or contact customer services.