What is sourdough bread?
Three ingredients and a great deal of time. There is no legal definition of the word sourdough in the UK, which is why two loaves labelled the same can be completely different things. Here is the whole process, and how to check a loaf before you buy it.
Three ingredients
Sourdough bread consists of only three ingredients: flour, water and salt. That is the whole list. Everything that makes it sourdough rather than ordinary bread comes from how those three are handled, not from anything else being added.
- 1FlourThe whole structure, and the food the culture lives on.
- 2WaterBrings the flour together and lets the fermentation happen.
- 3SaltSeasons the loaf and keeps the ferment from running away.
Where the rise comes from
A sourdough starter is made by mixing flour and water, then allowing naturally occurring microorganisms to establish a culture in this mixture over time. That culture is the only leavening in a real sourdough loaf. There is no packet of yeast.
When making a sourdough loaf, the dough ferments over several hours. The wild yeast and bacteria in the starter work more slowly than commercial yeast, and this slow fermentation is what produces the characteristic sourdough flavour. The sourness is not an ingredient. It is a by-product of waiting.
How long it actually takes
The whole process of making a sourdough loaf can range from approximately eight hours to a few days. Two things move that clock more than anything else.
| What changes | Towards 8 hours | Towards a few days |
|---|---|---|
| Room temperature | A warm kitchen. The culture is active and the dough moves quickly. | A cold kitchen. Everything stretches out, and the flavour sharpens. |
| Starter volume | More starter in the dough. More microorganisms, less waiting. | Less starter. A longer, gentler rise. |
This is why the same recipe behaves differently in January and July, and why a baker adjusts to the room rather than following a clock. A loaf is ready when the dough says so.
Why the label can lie to you
There is currently no legal definition of sourdough in the UK, which is why two loaves labelled the same can be completely different. Nothing has to be true before a loaf is sold under that name, which is very different from a protected term like Melton Mowbray pork pie.
Therefore, commercially produced loaves labelled as sourdough may contain commercial yeast and a relatively small volume of starter, or other flavourings used to imitate the classic sourdough taste. It is not fraud. It is a gap in the rules, 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
Turn it over and read the ingredients. A plain sourdough loaf should contain three things, and sometimes a fourth line that is really just the first two again.
What should be there
- FlourAny bread flour. Ours is strong white, with wholemeal or rye in some loaves.
- WaterThat is genuinely all.
- SaltFor flavour, and to slow the ferment to a workable pace.
- Starter, sometimes listed separatelyFine. A starter is only flour and water.
What means it is not sourdough
- YeastIf commercial yeast is doing the lifting, the long ferment is not.
- Acetic acid, or vinegarAdded to imitate the sourness a real ferment produces on its own.
- Emulsifiers and dough conditionersOften E numbers, or words ending in -ate. They make dough behave predictably at speed.
- Enzymes, or flour treatment agentIndustrial shortcuts for texture and shelf life.
- Palm oil or vegetable fatA plain sourdough does not need fat.
None of the items on the right are necessary for a genuine sourdough loaf. If they are in there, they are doing a job that time would otherwise have done.
One more test that costs nothing: watch how the bread ages. A genuine sourdough goes stale rather than mouldy, and it is still good toasted on day four. A loaf that is soft and identical on day six is being held that way by something.
What the slow fermentation actually does
To the flavour
The bacteria in the culture produce acids as they work, and the balance between them is what gives sourdough its character. A cooler, slower ferment pushes it towards the sharper end. A warmer, faster one gives something milder. Same three ingredients, different bread.
To the crumb
The open, irregular holes people photograph are a by-product of a well-developed dough and a strong ferment, not the goal in themselves. A tighter, 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.
If you are buying rather than baking
If you are paying a premium for sourdough, you are paying for hours or 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 quickly with commercial yeast and a splash of acid.
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.
We bake ours to order. Flour, water and salt, fermented for days, made for the Saturday you choose rather than baked ahead for a shelf.
See the bread counterIf 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 a plain 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
- What is sourdough bread?
- Sourdough bread consists of only three ingredients: flour, water and salt. It rises using a starter, which is flour and water left until naturally occurring microorganisms establish a culture in it. The wild yeast and bacteria in that starter work more slowly than commercial yeast, and that slow fermentation is what produces the characteristic sourdough flavour.
- How long does sourdough take to make?
- Roughly eight hours to a few days from start to finish, depending on the room temperature and how much starter goes into the dough. A warm kitchen and a generous amount of starter move it towards the short end. A cold kitchen and a small amount move it towards the long end.
- Is supermarket sourdough real sourdough?
- Some of it is and a lot of it is not. There is currently no legal definition of sourdough in the UK, so a commercially produced loaf sold as sourdough may contain commercial yeast, a relatively small volume of starter, or flavourings used to imitate the classic sourdough taste. The ingredients list is the only way to tell.
- How do I check whether a loaf is real sourdough?
- Read the ingredients. A plain sourdough loaf should contain flour, water and salt. Sometimes the starter is listed separately, which is fine, because a starter is only flour and water. Anything beyond that, commercial yeast, acetic acid, emulsifiers and so on, is not necessary for a genuine sourdough loaf.
- Is sourdough healthier than ordinary bread?
- The long fermentation does change the bread, because it begins breaking down starches and phytic acid before you eat it. That is why some people who find ordinary bread heavy get on better with it. It is still bread, and it is not gluten free, so anyone with coeliac disease should not eat it.
- Why is real sourdough more expensive?
- Time. A long ferment ties up space and labour for hours or days rather than minutes, and it cannot be rushed to meet demand. You are paying for the days, not for the flour.