pH Dynamics: Charting the Drop from 6.0 to 3.5

In baking, we are often told to watch the clock. "Bulk ferment for 4 hours." "Proof for 2 hours."

But biological time is not linear. It is exponential. And the true clock of sourdough is not measured in minutes, but in pH.

The transformation of dough from a simple mixture of flour and water into a complex, digestible, and flavorful loaf is driven by acidification. Understanding the curve of this drop is the difference between a loaf that is bland and gummy, and one that sings.

The Curve: A Tale of Two Acids

When you mix your dough, it starts at a near-neutral pH of roughly 6.0.

As fermentation begins, the Lactic Acid Bacteria (LAB) wake up. They consume maltose and excrete organic acids. But they do not do this at a constant rate.

1. The Lag Phase (pH 6.0 - 5.5):

   For the first few hours, the pH drops slowly. The bacteria are acclimating. The dough still smells like wet flour.

2. The Log Phase (pH 5.5 - 4.5):

   This is the acceleration. The population explodes. Lactic acid production ramps up. The dough begins to smell creamy and yogurt-like [1].

3. The "Sour Spot" (pH 4.1 - 3.8):

   This is the target window for baking.

   • At pH 4.1: The protease enzymes are activated (softening the gluten) [2].

   • At pH 3.8: The flavour complexity peaks (balance of lactic/acetic).

   • Below pH 3.8: The gluten network begins to break down too much. The dough becomes sticky and weak.

Why the Drop Matters

The pH is not just a flavour dial; it is a master switch for chemistry.

• Structure: Gluten proteins change their charge as the pH drops. Around pH 4.0, they swell and hold water better. But go too low, and they unravel (liquefaction) [3].

• Enzymes: Amylase activity is regulated by pH. If the dough is too acidic, amylase stops working, potentially leaving the yeast without fuel. Conversely, protease needs acidity to work.

Managing the Drop

You cannot see pH, but you can taste and smell it. Or, for the precise baker, you can measure it.

• Sensory: A "ripe" starter or dough will smell sharply sour, not just yeasty. It will taste like a lemon drop—clean, sharp, and acidic, distinct from the harshness of vinegar [4].

• Tools: A simple pH meter is the secret weapon of the modern sourdough baker. It removes the guesswork of "is it ready?"

Summary

Time is a guideline. pH is the reality.

By charting the drop in acidity, you are tracking the heartbeat of your culture. You are baking not by the clock on the wall, but by the biological clock in the bowl.

References

1. Gänzle, M. G. (2014). Enzymatic and bacterial conversions during sourdough fermentation. Food Microbiology.

2. Clarke, C. I., et al. (2004). Wheat Sourdough Fermentation: Effects of Time and Acidification on Fundamental Rheological Properties. Cereal Chemistry.

3. Arendt, E. K., et al. (2007). Impact of sourdough on the texture of bread. Food Microbiology.

4. Hansen, A., & Schieberle, P. (2005). Generation of aroma compounds during sourdough fermentation: applied and fundamental aspects. Trends in Food Science & Technology.

5. De Vuyst, L., & Neysens, P. (2005). The sourdough microflora: biodiversity and metabolic interactions. Trends in Food Science & Technology.