Researchers Track Every Hour of Sourdough Starter Growth After Feeding

Most sourdough bakers judge their leaven by eye and nose: wait for the dome, check for bubbles down the glass, press a fingertip to the surface. A new multidisciplinary study put instruments where the intuition usually goes.

The paper, titled "A Day in the Life of a Sourdough Leaven from Feeding to Maturity," follows a mature flour-water leaven through a complete 24-hour fermentation cycle after a 20-fold feeding. That ratio, far more dilute than the 1:1:1 or 1:5:5 refreshments most home bakers use, was chosen deliberately: it gives the microbial community enough runway to reveal the full arc of activity from the moment fresh flour hits the culture to the point the leaven exhausts its fuel.

The team tracked pH and CO2 production across the entire window, turning what bakers observe macroscopically into a quantified timeline. Time since feeding is a foundational variable in sourdough science, and each refreshment effectively triggers a reset in which all microorganisms must adjust to the new environment before reaching peak fermentative activity. This study documents exactly how that adjustment unfolds, hour by hour.

The underlying biology the researchers were chasing is well understood at a qualitative level. Sourdough is a specific and stressful ecosystem harboring yeasts and lactic acid bacteria, and the metabolic impact most noticeable to bakers is acidification from LAB, flavor formation from both LAB and yeasts, and leavening driven by yeasts and heterofermentative LAB species. What has been harder to nail down is the precise sequence and timing of those contributions inside a single feeding cycle.

The pH data the team collected matters practically. Bacterial metabolism lowers pH during fermentation, and that drop activates endogenous proteases, the primary drivers of protein breakdown; the acidic pH further activates proteinases responsible for gluten degradation, while an accumulation of low-molecular-weight thiols increases gluten solubility by decomposing intermolecular disulfide bonds. Knowing at which hour these shifts are most pronounced gives bakers a more precise target than the traditional float test.

The 20-fold feeding also has real implications for the leaven's microbial balance across the cycle. How much flour and water you add in proportion to the starter determines how fast the culture rises: the higher the feeding ratio, the more time it takes for the starter to consume all its food and the longer it takes to reach peak ripeness. A 20-fold dilution stretches that arc considerably compared to a standard daily refresh, making it easier to capture intermediate states that would otherwise be compressed or missed entirely.

The paper is published open-access, meaning the full dataset and methodology are available without a paywall. For bakers who have always wanted to know what is actually happening inside the jar between the feed and the float test, this is the most detailed answer yet produced.