The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Sourdough Nutrition

Doc Tracy's picture
Doc Tracy

Sourdough Nutrition

Does anyone have any data on how much sourdough starter changes nutrition in bread? I'm curious to know how much the starter converts carbs to amino acids and other nutrients. I guess it would be very difficult to calculate because it would depend on length of fermentation, original quantity of starter, number of yeasties and other buglets in the starter. But, just wondering if anyone has done any sort of research/calculations of this sort?

I couldn't find anything on this when I did a web search.

Thanks, Tracy

Ford's picture

Since carbohydrates are by definition composed of only carbon, hydrogen, and oxygen, and since fermentation does not involve a nuclear reaction to convert any of these elements to nitrogen, there is no conversion of carbohydrates to either amino acids or to proteins.  There is some conversion to sugars, alcohols, aldehydes, acids, and of course carbon dioxide.

just an old chemist,


Doc Tracy's picture
Doc Tracy

Hmm- the bacteria and yeast have to eat something. Also, they multiply and are made of amino acids. Where do the raw materials come from and how do their raw materials factor into the final nutrition? I'd think that they would add to the protein content as well. My understanding is that they convert carbs to amino acids by using the energy for metabolism.

rockfish42's picture

They create amino acids just like everything else, also they probably break down proteins in the flour and reconfigure them for their own needs.
Look up amino acid synthesis and protein biosynthesis for more details,

Other than reducing the glycemic load of the bread and deactivating phytase in whole grains making minerals more available, there aren't any drastic changes in nutrition. If you think about it the only thing leaving the close system on a molecular level is a nominal amount of CO2 and water vapor during the bake.

Sam49's picture

There is a substantial body of research from around the world that shows that the lactobacilli in sourdough also break down gliadin - the chemical that triggers the adverse response in those with celiac disease and other gluten intolerances.

The degree to which this happens depends on the strains of lactobacilli in a particular starter and the length of time of fermentation. 

Google "sourdough gliadin" and you'll find some of it.

Some people read this and generalize to state that celiac folks can eat sourdough.  That is an overstatement.  Not all strains eliminate all the gliadin - in fact few do - and then only with long fermentation.  Some people have milder intolerances than others.


Ho Dough's picture
Ho Dough

The thought on my end being if you only use water, flour and salt as ingredients, and the yeast and bacteria are forced to live on that, they are going to "mine" the carbohydrates out of the flour, leaving only the proteins, minerals, etc., very similar to what happens with most alcohol producing fermentations. With any starter culture or dough proof, let it go too long and it falls flat.....suggesting this happens in a hurry. The same thing may happen with with long fermentations of wet doughs using commercial yeasts, which have the ability to break down and metabolize maltose. Maybe even more so than with sourdoughs.

The benefit flows to diabetics, and those on low carb diets who need to avoid most breads. On the glycymic index, sourdough is at the "low" end, suggesting some of this is going on. Regular breads are medium to high.

But as for how to measure, a biochemist may be able to take a swag at it if they could measure the weight of the ingredients going in and weight of bread loaf going out. You would be missing the weight of the CO2 and alcohols, complicated by the loss of water to evaporation during proofing and baking. Changes in pH might also tell you something.