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Sourdough bread mythbuster

Real Bread Campaign coordinator Chris Young tries to separate the wheat from the chaff.

A sourdough starter. Credit: Canva

A sourdough starter. Credit: Canva

We at the Real Bread Campaign love all Real Bread and the people behind its rise. During September, we focus on celebrating genuine sourdough bread in particular. 

We are, however, careful to ensure that our passion doesn’t get the better of us when explaining why we think that genuine sourdough bread is so great.

Not all loaves are created equal

The following is all in addition to the potential benefits of buying Real Bread (ie additive-free) from a local, independent bakery, or making your own. 

There is a growing body of evidence (including many peer-reviewed studies, plus people reporting their own experiences) that leads us to believe that there *MIGHT* be a range of benefits of eating bread made by the sourdough process.

BUT…

  • Every sourdough starter and bread made from it is different. The species and strains of yeasts and lactic acid bacteria in each sourdough starter culture is unique.
  • There are very specific conditions for each study done. The results and conclusions of / benefits reported by a study carried out using a starter of a particular flour at X hydration, containing lactic acid bacterium Y and yeast Z, fermented for A minutes at B degrees, might not necessarily apply to every (or any) other sourdough starter culture. Many scientific studies are carried out on animals or in vitro (test tubes, petri dishes etc.) and the results in human beings going about their everyday lives might be very different.
  • One swallow does not a summer make. Even if conclusive, results of a single study (particularly one involving only tens or even hundreds of participants/subjects) can’t necessarily be extrapolated to apply to all sourdough bread made in exactly the same way as used in the experiment/study. 
  • You are unique. What is true for you might not be for someone else. The very real reaction of your body (and your microbiome) to eating a slice from a loaf might well differ to that of another person eating a slice from the same loaf.
  • The Great Britian Nutrition and Health Claims Register includes none specific to sourdough fermentation. It is not legal to make a nutrition or health claim that isn't on the register. Read governmental guidance.

Always read the label

Without the legal definition of sourdough we call for as part of our Honest Crust Act lobbying, a manufacturer or retailer can name/market pretty much anything using the word.

Even if any benefit of sourdough fermentation is proven beyond doubt somewhere down the line, the changes upon which the benefit relies cannot occur if a live sourdough starter culture is not used, or occur to the same extent if the lactic acid bacterial fermentation is shortened by the addition of baker’s yeast. Say no to sourfaux!

If you want the real thing, you can search the Real Bread Map (some listed bakeries sell only sourdough, some sell Real Bread made using baker's yeast) and look for The Sourdough Loaf Mark. The only way to be sure that you’re getting genuine sourdough bread, however, is to check (or ask for, if the product is sold unwrapped) the ingredients list. It can include any number of natural ingredients but if the word yeast appears (see notes below) or any additives are listed, it is not what we call genuine sourdough bread. 

Sourdough is…

Here are notes on some of the claims we often see being made.

More nutritious
It depends.
The vitamin and mineral content of bread mainly depends on the flour used. In the UK, iron, calcium and synthetic forms of two B vitamins have to be added to most non-wholemeal flour by law. This means that, on paper, levels of those four in white flour and products made from it should be as high (and possibly higher than) in wholemeal.

…but that’s only four of a whole rainbow of micronutrients that are stripped and sifted away in the roller milling process to produce refined flour.

…and even as far back as 1981, a governmental advisory committee cast doubt on the benefit of iron in the form in which it is added, questioning its bioavailability – meaning how readily the body can make use of it.

At the same time, research indicates that the sourdough fermentation process might improve our ability to make use of some of the micronutrients in flour. Phytate, or phytic acid, is a nitrogen storage compound found in plants – particularly in bran and other seed casings, so wholemeal flour has plenty. It is sometimes known as an ‘anti-nutrient’ because it binds with certain micronutrients, making them less bioavailable for our bodies to use. Evidence suggests that lactic acid bacterial fermentation might favour greater activity of phytase, an enzyme that breaks down phytate. Increased phytase activity means reduced levels of phytic acid, which means we get more benefit from the micronutrients, rather than them passing straight through.

Higher in fibre
It depends.
As with micronutrients, fibre content is down to the flour used. Though some Real Bread bakers use less-refined, higher-fibre flours to make sourdough bread, it can also be made from brown or white flour. An additive-laden, Chorleywood Process industrial loaf product made from wholemeal flour has more fibre than a genuine sourdough bread made from highly-refined white. Sourdough fermentation might increase levels of resistant starch and other soluble fibres, though.

More digestible. 
It depends.
There isn’t a universally-agreed marker of digestibility. Some (not all) people who experience discomfort eating unleavened bread and/or products made using baker’s yeast, report they can enjoy eating genuine sourdough bread. In some cases, this might be down to sourdough fermentation, then again might it be down to one or more other factors, such as the flour used or absence of additives?

Gluten-free
Only if it’s made from gluten-free flour.

Lower in gluten
No, not significantly.
There is some evidence that the sourdough fermentation process might modify, and even reduce levels of, gluten proteins, but not to the point of being able to say sourdough bread is lower in gluten. If you reduce the gluten in wheat-based dough to a significant extent, you’ll end up with something pretty dense, or even flat.

…but, some people who experience discomfort or other difficulty eating industrial loaf products (or even Real Bread) made using baker’s yeast report that they can enjoy genuine sourdough bread. Might gluten modification during the sourdough fermentation process be the reason for some of those people?

Lower in FODMAPs
Maybe.
Fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) are short-chain carbohydrates. They aren’t easily absorbed through the lower intestine, where they attract water and ferment, triggering symptoms in people with conditions such as irritable bowel syndrome (IBS). FODMAP levels depend mainly on the flour used. For example, rye is very high in FODMAPs, spelt is lower (though still high) and modern/bread wheat is somewhere in between. Wholemeal flours are higher in FODMAPs than white/refined flours. Research suggests that sourdough fermentation might reduce FODMAP levels.

Lower GI
Maybe.
Glycaemic index (GI) is a ratings system of how quickly a food is likely to raise blood sugar levels. A hit of pure glucose is rated at 100, while more complex carbohydrates that take longer to be metabolised into simple sugars have lower numbers. Spikes in blood sugar are an issue for people with conditions including diabetes, and evidence suggests the rest of us might also benefit from smoothing out peaks and troughs in our blood sugar levels.

Bread (and industrial loaf products) made from refined wheat flour has a very high glycaemic index. Wholemeal is metabolised more slowly and has a slightly lower GI, but it’s still fairly high. Some studies have found that sourdough fermentation might reduce the GI of the resulting bread, while other have been inconclusive.

Sour
Not necessarily.
Given the name, you’d be forgiven if you think that bread this way is all tangy (especially if you know that bacteria that produce lactic acid are involved) but sourdough bread does not have to be sour! Any bread (sweet or savoury) that can be made using baker’s yeast can be made by the sourdough process. Yup, even brioche, doughnuts, panettone, a white sandwich loaf and so on. If a bread is sour, it’s probably because the baker has chosen to make it that way.

Yeast-free
No.
Though industrially-cultured baker’s yeast (each brand being a monoculture of one of many strains of Saccharomyces cerevisiae) isn’t used in making genuine sourdough bread, every sourdough starter culture contains one or more species of yeast. In some cases, the yeast might include S. cerevisiae, though almost certainly not any of the strains monocultured by bakery ingredients manufacturers.

(Bakers, if for some reason you feel you really need to make a marketing claim, you can say 'made without baker's yeast' but we think it's better to let its absence from the ingredients list do the talking.)

Prebiotic and probiotic
Yes and no
There is not yet complete consensus on exactly what the term prebiotic means. One rough definition is that it is something (generally a type of fibre or other non-digestible carbohydrate) that can be used by intestinal microorganisms to produce compounds that are beneficial to them, and consequently help them to generate benefits to the host. Sourdough fermentation might increase levels of resistant starches (RS) and other prebiotics – though not everyone agrees that RS are strictly speaking prebiotics.

A food that is probiotic contains microorganisms that remain viable/alive in the digestive tract and so can be beneficial to the host. While some of the yeasts and bacteria found in some sourdough starters might be probiotic, you're (probably) not going to drink/eat a starter culture or raw bread dough. Sourdough bread is not probiotic because the microorganisms are killed/denatured by the heat of baking. 

Sourdough bread might contain some post-biotics, though. These are residues and byproducts of microbial activity, some of which might be beneficial to us.    

Tastier
Hell, yeah!
Okay, sorry. Let the objectivity slip for a moment there. This one really is down to your tastebuds. If you love it, you love it. If you don't, you don't.

As previously noted, ‘sourdough’ isn’t a single, uniform thing. Burger X from multinational chain Y is pretty much the same object in any and every one of its outlets globally. By contrast, a single bakery might produce two or ten sourdough breads that taste totally different from each other. Given all of the variables, the style, type, textures and flavours of bread that can be made by the sourdough process are infinite. 

This also means that ‘I don’t like sourdough’ is a bit like saying you don’t like chocolate, cheese or beer. What you probably mean is that you haven’t yet (knowingly) tried a bread made by the sourdough process that you like. Then again, maybe what you mean is that you just don’t like bread.

…oh, and a skilled Real Bread baker (actually, even the less skilled amongst us) can make additive-free bread using baker’s yeast that many people find delicious.

We call for more research!

‘Why does the Real Bread Campaign bang on about sourdough so much if none of the possible benefits has been proven beyond doubt?’

Call it a case of no smoke without fire, if you like. There is an ever-growing shedload of compelling evidence indicating that benefits outlined above (and more) might result from sourdough fermentation of bread dough. We believe that it is more than enough to warrant further research to determine which benefits can be ruled out and which can be stated as fact, either by meeting very specific criteria or for sourdough bread in general.

So, come on governments, the industrial baking sector and other funders: please stump up the dough to get that research done!

Careful with those claims

To everyone making claims about sourdough bread in the meantime, please, please help to maintain credibility of the arguments by being as specific as possible and qualifying them with ‘might’, ‘maybe’, ‘according to study X’, ‘some people find’ and similar caveats.

For bakers and retailers, if your advertising/marketing (including your website, emails, and social media) includes anything that could be considered a health of nutritional claims (high in fibre, low in fat, a good source of vitamin Z, promotes a glossy coat, that sort of thing), you need to be sure it's one that's legally permitted. If it isn't, you could get into trouble with the trading standards department of your local authority and/or the Advertising Standards Authority. 

As noted at the start of this article, The Great Britian Nutrition and Health Claims Register includes none specifically to sourdough fermentation.

The UK's advertising codes include sections on nutrition and health claims, plus the requirement that: 'Marketing communications must not suggest that their claims are universally accepted if a significant division of informed or scientific opinion exists.'

Please read 

  • Governmental guidance on nutrition and health claims.
  • The BCAP Code (The UK Code of Broadcast Advertising), particularly section 13.
  • The CAP Code (The UK Code of Non-broadcast Advertising and Direct & Promotional Marketing), particularly section 15.

End crust

I’ll leave the last word for now to the authors of Nutritional benefits of sourdoughs: A systematic review:

“Overall, it is currently difficult to establish a clear consensus with regards to the beneficial effects of sourdough per se on health when compared with other types of bread because a variety of factors, such as the microbial composition of sourdough, fermentation parameters, cereals, and flour types potentially influence the nutritional properties of bread. Nonetheless, in studies using specific strains and fermentation conditions, significant improvements were observed in parameters related to glycemic response, satiety, or gastrointestinal comfort after bread ingestion. The reviewed data suggest that sourdough has great potential to produce a variety of functional foods; however, its complex and dynamic ecosystem requires further standardization to conclude its clinical health benefits.”

Find out more

As noted above, there has been, and continues to be, a large number of (generally small scale) studies into the effects of sourdough fermentation. Academic papers and journals can be found through databases including ScienceDirect, PubMed, JSTOR and Directory of Open Access Journals.

Reviews and metanalyses of papers published about sourdough research include:

See also

Published 25 Sep 2023

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