How to make sourdough bread more or less acidic

The acidity of sourdough bread comes primarily from two organic acids produced by bacteria during fermentation: lactic and acetic acids. Lactic acid has a mild, almost yogurt-like flavor and contributes to the creamy texture of well-made bread. Acetic acid is stronger and more pungent, the same acid found in vinegar, and is the only one that can be smelled in the dough.

Bacteria are sensitive to the pH of the dough. As they produce acid, the pH drops until the acidity itself slows their activity. Anything that allows them to work longer before reaching that point, such as the greater buffering capacity of whole grains, prolonged fermentation, or warmer temperatures, increases the overall acidity.

For a more acidic bread, the simplest way is to use sourdough starter that has already passed its peak: it has a pungent, acidic aroma, a loose consistency, and has deflated in the jar. The most reliable technique, however, is to extend the fermentation in the refrigerator. Between 12 and 16 hours in the refrigerator is typical; after 24, 48, or even 72 hours, the acidity becomes increasingly pronounced. The drawback is that the natural enzymes break down the gluten over time, and the dough is less firm in the oven.

A firm sourdough starter, with a hydration level between 50 and 65%, promotes acetic acid production if allowed to mature long enough. Wholemeal flours also increase acidity due to their ash content, which acts as a natural buffer. Rye is particularly effective: even small percentages significantly enhance the acidic flavor.

Warm temperatures, between 25 and 28 °C, favor bacterial activity and produce more acid overall, while cold temperatures favor acetic acid, although the total production is lower. Using less sourdough starter also helps: a large, very mature starter lowers the pH from the beginning, leaving the bacteria less room to continue acidifying.

For less acidic bread, it's best to keep the starter well-fed and use it at its peak, when it forms a dome on the surface and bubbles, before it develops an excessively sour aroma. A young sourdough starter, made with equal parts flour, starter, and water, fermented at 25-27°C for 3-4 hours, contributes less acidity. Shortening the cold fermentation to 10-12 hours instead of 16-18, or using a liquid sourdough starter with 100% hydration, also softens the flavor.

A longer cold fermentation doesn't just accentuate the acidity. After 24 hours, the dough can over-ferment, lose structure, and rise poorly in the oven, so it's best to keep a close eye on it.

If the bread simply tastes like bread, the most likely causes are a culture of less than two or three weeks, a sourdough starter used before maturing, a fermentation that is too short, a kitchen temperature above 27°C, or the exclusive use of refined white flour with low ash content.