The pH Of Sourdough Bread: The Significance of Acidity

Despite being an ancient process, sourdough bread has recently gained widespread popularity for its unique taste, texture and health benefits. One aspect that plays a crucial role in sourdough bread is its pH level. In this article, we will delve into the significance of pH in sourdough bread, the factors influencing pH, and its implications on the final product.

Understanding pH

pH is a measure of acidity or alkalinity on a logarithmic scale ranging from 0 to 14. A pH of 7 is neutral, while values below 7 indicate acidity. Values above 7 indicate alkalinity.

Typical bread made with yeast has a pH level of 5.0 – 6.5, making it slightly acidic but so mild that its acidity is unnoticed by most people.

For sourdough bread, pH levels typically fall between 3.5 and 5.5, making it mildly acidic. 

Influence of pH on Sourdough Bread

Acidity is developed by yeast and organic acid bacteria producing lactic and acetic acids in the sourdough fermentation process. pH plays a significant role in the development and characteristics of sourdough bread. It affects the following aspects:

Flavour

The pH level influences the flavour profile of sourdough bread. The acids produced during fermentation contribute to sourdough’s characteristic tanginess that sets it apart from regular bread.

Texture

Gluten is the collection of proteins which bond to form a structure (or gluten network) which gives bread its shape. The gluten structure holds the bread together and captures gas, enabling it to rise.

Acidity, primarily lactic acids, degrade gluten. Whilst some degradation makes the bread’s crumb soft and light, a long fermentation period damages the gluten structure. The weakened network is prevented from retaining gas effectively, meaning the bread will not rise to its potential, and, in extreme cases, your bread can collapse.

Crumb composition

Higher acidity is thought to encourage an open crumb structure in bread. The acids repel against other products in the dough, forcing the gluten structure to split and form irregular bubbles.

A common sign of bread that’s under-fermented or made with a weak starter is a compact crumb -caused by a lack of acidity.

Shelf Life

The acidity of sourdough bread helps inhibit the growth of spoilage-causing microorganisms. Low pH creates an unfavourable environment for mould and bacterial growth, naturally extending the bread’s shelf life.

Factors influencing pH in a sourdough starter

Yeast-risen bread will develop acidity if the dough is left to ferment for several hours. But a sourdough starter is used to drop bread pH further.

A starter is a culture of wild yeasts and organic acids that collectively ferment the flour’s sugars to make gas. Other products produced through fermenting flour and water include; water, ethanol, esters, lactic acid, acetic acid, vinegar and acetyl.

So, how can you make your sourdough starter have a lower pH? Well, I’ve already written a comprehensive guide on how to make a sourdough starter more acidic, which, if you haven’t already, I suggest reading after this! It essentially comes down to four points:

• Starter maturity
• The feeding point
• Fermentation temperature
• Viscosity

Factors Influencing pH in Sourdough Bread

Several factors contribute to the pH of sourdough bread:

Fermentation Time

The longer the fermentation process, the more acids are created, lowering the pH level.

Starter Composition

The microbial composition of the sourdough starter significantly impacts pH. Different strains of lactic acid bacteria and wild yeasts in the starter produce varying quantities of acids, resulting in different pH values.

Temperature

Fermentation temperature influences the activity of microorganisms. Warmer temperatures accelerate fermentation, producing more acid and lower pH.

Hydration Level

The hydration level of the dough affects its pH. A higher hydration level accelerates fermentation activity which can lead to a slightly lower pH.

Acidic additions

Only the most robust yeast strains survive inside the low-pH environment of a sourdough starter. Adding extra acidic ingredients (lemon, citric acid, vinegar) to your sourdough bread recipe makes it harder for the yeast cells to work.

As the fermentation process of acetic acid produces around half the carbon dioxide required to raise sourdough bread, extra acidity won’t entirely result in a flat loaf. But yeast cells in an extremely low pH dough will be less effective, slowing the dough’s rise.

How to test the pH value in sourdough bread?

Well, for most of us, you don’t! Whilst it might be tempting to pull out a pH meter in the back of your garage. It’s not going to work.

For reasons outlined in the video below, there are several complicated steps you need to take to test the pH of sourdough with accuracy.

Video courtesy of Karl from The Sourdough Library.

Conclusion

The pH level is critical in sourdough bread production, influencing its flavour, texture, and shelf life. Understanding the factors that affect pH, such as fermentation time, starter composition, temperature, and hydration level, will help you to create the ideal flavour texture and shelf life in your sourdough bread!