What You’ll Learn
- What lactic acid bacteria are.
- What acids they produce.
- How they affect flavour.
- Why acidity matters.
- How bacteria and yeast coexist.
Quick Answer
Lactic acid bacteria are a major part of sourdough starter. They consume sugars and produce acids, especially lactic and acetic acids. These acids shape flavour, lower pH and help create the stable environment that distinguishes sourdough from ordinary yeast bread.
This lesson is part of our Science of Sourdough section: “Understand what’s happening inside your dough.”
What Are Lactic Acid Bacteria?
They are acid-producing bacteria that thrive in the flour-and-water environment of a mature starter.
What Do They Produce?
Depending on species and conditions, they can produce lactic acid, acetic acid and other flavour compounds.
Why Does pH Fall?
As acids accumulate, the starter becomes more acidic. This shapes which microorganisms are able to thrive.
Flavour
Lactic acid tends to taste softer and yoghurt-like, while acetic acid contributes sharper vinegar-like notes.
Relationship With Yeast
Yeast and bacteria share the same ecosystem and use different nutrients and metabolic pathways.
Why This Matters in Bread
The balance of acids affects flavour, gluten behaviour, fermentation and keeping quality.
Why This Matters in the Kitchen
The science matters only when it helps you make better decisions. Use it to understand what you can see, smell and feel in your starter and dough.
From Our Workshop
Sourdough is not ‘wild yeast bread’. It is a yeast-and-bacteria ecosystem, and leaving the bacteria out of the explanation misses half the story.
Bake Slower Tip
Smell your starter through a full feeding cycle. Aroma gives you clues about acid development.
Common Mistake
Do not assume all sourness comes from one type of acid.
Today You Learned
- Lactic acid bacteria are essential to sourdough.
- They produce acids and flavour compounds.
- Acidity lowers pH.
- Different acids create different flavour profiles.
- Yeast and bacteria work in the same ecosystem.
Frequently Asked Questions
Are lactic acid bacteria safe?
The established sourdough ecosystem is widely used in food fermentation, but contaminated starter should still be discarded.
Do bacteria make the bread rise?
Yeast is the main gas producer, though bacterial metabolism also affects fermentation.
Why is my starter tangy?
Acids produced by bacteria are a major reason.
Can temperature change bacterial activity?
Yes.
Does feeding ratio affect acidity?
Yes, because it changes the amount of fresh food relative to accumulated acids.
Tools & Ingredients Mentioned in This Guide
These products are directly related to the measurements, ingredients or starter care discussed in this lesson.
Turn the Science Into Better Bread
Once you understand the bacteria as well as the yeast, sourdough flavour becomes much less mysterious.
Continue Learning
Next lesson: Fermentation in Sourdough
What this means at the bench
The useful question is not only what is happening scientifically, but what you can observe. Connect the science to changes in rise, aroma, acidity, dough strength, extensibility and fermentation speed in your own kitchen.