What real sourdough actually is
There is no legal definition of the word sourdough in the UK. That single fact explains almost everything confusing about buying it, and it is why two loaves labelled the same way can be completely different things.
Three ingredients, and time
Real sourdough is flour, water and salt. That is the whole list. The rise comes from wild yeast and lactic acid bacteria living in a starter, which is simply a paste of flour and water that has been kept alive and fed. No commercial yeast goes in. Nothing else goes in.
What makes it sourdough is not an ingredient at all. It is the time. Those bacteria work slowly, and a proper ferment takes somewhere between twelve hours and several days depending on the flour, the starter and how warm the room is. That slowness is the entire product.
Why the label can lie to you
In the UK, "sourdough" is not a protected term. There is no legal standard a loaf has to meet before it can be sold under that name, which is very different from something like Melton Mowbray pork pies or Cornish pasties.
So a large bakery can make a loaf in a few hours using commercial yeast, add a small amount of fermented flour or an acid for the tang, shape it to look rustic, dust it with flour, and legally sell it as sourdough. It is not fraud. It is a gap in the rules. The industry name for this is sourfaux, and the Real Bread Campaign has been arguing for years that honest labelling should be required.
The crust tells you nothing. Anyone can dust flour on a loaf and score it with a blade. The ingredients list is the only thing that cannot be styled.
How to check a loaf in ten seconds
Turn it over and read the ingredients. You are looking for exactly three things: flour, water, salt. Some bakers list the starter separately, which is fine, because a starter is only flour and water.
These are the words that mean it is not sourdough:
- Yeast, in any form. If commercial yeast is doing the lifting, the long ferment is not.
- Vinegar or acetic acid. Added to imitate the sourness a real ferment produces on its own.
- Emulsifiers and dough conditioners, often listed as E numbers or things ending in -ate. They exist to make dough behave predictably at speed.
- Enzymes or "flour treatment agent". Industrial shortcuts for texture and shelf life.
- Palm oil or vegetable fat. Real sourdough does not need fat.
One more test that costs nothing: look at how long the bread stays good. A genuine sourdough goes stale rather than mouldy, and it is still decent toasted on day four. A loaf that is soft and identical on day six is being held that way by something.
What the long ferment actually does
To the flavour
Lactic acid bacteria produce two acids as they work, and the balance between them is what gives sourdough its character. Cooler, slower fermentation pushes it towards the sharper, more vinegary end. Warmer and faster gives something milder and more yoghurty. This is why the same recipe tastes different in January and July, and why a good baker adjusts rather than following a script.
To the crumb
The open, irregular holes people photograph are a by-product of a well-developed gluten network and a strong ferment, not the goal in themselves. A tight, even crumb is not a failure. For a sandwich it is better.
To how it sits with you
Fermentation begins breaking down starches and phytic acid before the bread ever reaches the oven, work your digestion would otherwise have to do. That is the honest, non-miraculous version of why some people find real sourdough easier going than fast-made bread. It is not a health food and it is emphatically not gluten free, but it is bread that has been partly digested by microbes before you get to it.
Why this matters if you are buying rather than baking
If you are paying a premium for sourdough, you are paying for days of someone's time and oven space. That is a fair thing to pay for. It is not a fair thing to pay for when the loaf was made in three hours with yeast and a splash of vinegar.
So ask the baker how long their ferment is. Anyone doing it properly will tell you immediately and probably at length, because it is the thing they are proudest of. A shrug is an answer too.
If you want to try it yourself
Start with the starter, because nothing else is possible without it and it is the part most people give up on. We wrote aplain guide to getting a sourdough starter going that covers the first two weeks honestly, including the stage where it looks dead and is not.
Questions we get asked
- Is supermarket sourdough real sourdough?
- Some of it is. A lot of it is not. In the UK there is no legal definition of sourdough, so a loaf can be made in a few hours with commercial yeast, have a little fermented flour or vinegar added for tang, and still be sold as sourdough. Read the ingredients: real sourdough needs flour, water and salt, and nothing else.
- What is the sourdough loaf test?
- Look at the ingredients list, not the crust. If you see yeast, dough conditioners, emulsifiers, vinegar or anything ending in -ate, it is a yeasted bread with sourdough characteristics rather than sourdough. A real one lists flour, water and salt.
- Is sourdough healthier than normal bread?
- The long fermentation does change the bread. It breaks down some of the starches and phytic acid before you eat them, which is why some people who find ordinary bread heavy get on better with it. It is still bread though, and anyone with coeliac disease should not eat it: sourdough is not gluten free.
- Why is real sourdough more expensive?
- Time. A long ferment ties up space and labour for days rather than hours, and it cannot be rushed to meet demand. You are paying for the days, not the ingredients.