What is Acetic Acid in Sourdough Baking?
Acetic acid is an organic acid produced by bacteria in the sourdough starter during fermentation. It contributes to sourdough’s distinctive tangy flavour and acts as a natural preservative, extending the bread’s shelf life by inhibiting spoilage microorganisms. Acetic acid is formed primarily by lactic acid bacteria (LAB), such as Lactobacillus sanfranciscensis, as they break down carbohydrates, playing a crucial role in balancing flavour, digestibility, and the overall microbial environment of sourdough.
Why is Acetic Acid Important?
Acetic acid influences both the sensory and functional qualities of sourdough bread. Its presence can:
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Enhance flavour – Acetic acid, along with lactic acid, is responsible for sourdough’s signature tangy taste.
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Improve shelf life – The acidic environment inhibits mould growth and slows staling, acting as a natural preservative.
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Support gut health – Acetic acid may contribute to gut microbiome balance by promoting beneficial microbes and aiding the digestion of gluten and other compounds.
How is Acetic Acid Formed?
Acetic acid is produced by acetic acid bacteria during the fermentation process, particularly in the presence of oxygen. Factors that influence its production include:
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Fermentation temperature – Cooler temperatures (below 25°C) encourage higher acetic acid production.
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Hydration levels – Lower hydration dough (stiffer dough) favours acetic acid formation.
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Flour choice – Whole grain flours provide more complex carbohydrates that influence acid production.
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Fermentation time – Extended bulk fermentation allows for greater acid production.
Acetic Acid and Digestibility
The presence of acetic acid in sourdough contributes to the breakdown of gluten and phytic acid, enhancing the bioavailability of essential nutrients. Research on fermentation and gut microbiome suggests that acetic acid in sourdough may improve digestion, making it easier to tolerate for individuals with gluten sensitivity or IBS. Additionally, acetic acid fosters an environment that supports the growth of beneficial gut bacteria, promoting a healthier microbiome. At The Sourdough School we use an evidence based protocol to make bread that can help with gluten sensitivity, IBS, bloating, tiredness, constipation, blood sugar balance, stress management and supports mental health. Find out more about it here.
How to Control Acetic Acid Levels in Sourdough
Bakers can adjust fermentation conditions to influence the level of acetic acid in their bread:
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Lower the fermentation temperature to encourage more acetic acid development.
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Use a stiff starter (lower hydration) to shift fermentation towards acetic acid production.
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Extend the bulk fermentation time to allow bacteria more time to process carbohydrates.
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Adjust oxygen exposure – Some oxygen presence can stimulate acetic acid bacteria, but too much can disrupt balance.
