Fermentation Science: the numbers behind a good rise
Bulk fermentation typically runs 4 to 6 hours at 75°F, but that time roughly halves for every 10-degree rise in dough temperature — which is why the same recipe behaves completely differently in summer versus winter. This hub covers the science behind bulk fermentation, hydration percentages from 65 to 85%, autolyse, and baker's percentages for scaling recipes accurately. The hydration calculator and bulk ferment timer turn this science into a specific number for your kitchen.
Helpful tools for this topic
Free and no sign-up needed. These tools do the calculating and planning for you.
All guides on Fermentation Science
Open Crumb vs Tight Crumb Explained
Open crumb gets all the Instagram love, but tight crumb has its own advantages. Here is what determines crumb structure and how to control it in your bakes.
Read guide →
Five Ways to Make Sourdough More Flavorful
If your sourdough bread tastes bland or one-dimensional, these five simple changes will unlock deeper, more complex flavors in every loaf.
Read guide →
Sourdough Hydration Experiments: What I Learned Baking at 60%, 70%, 80%, and 90%
I baked the same recipe at four different hydration levels to show exactly how water changes your bread. Here are the results with photos, tasting notes, and practical recommendations.
Read guide →
Mastering Bulk Fermentation for Sourdough Bread
Read guide →
The Science of Sourdough Fermentation: What Is Actually Happening in Your Dough
Understanding the biology and chemistry behind sourdough fermentation helps you make better decisions at every stage. Here is what wild yeast and bacteria are doing in your dough.
Read guide →
Understanding Sourdough Hydration: What the Percentages Mean
Read guide →
Sourdough Glossary: 20 Terms Every Beginner Should Know
From autolyse to windowpane, these are the sourdough terms you will encounter everywhere. A quick-reference glossary so you never feel lost reading a recipe again.
Read guide →
Cold Retard Overnight: More Flavor, Less Effort
Cold retarding your sourdough in the fridge overnight gives you deeper flavor, better scoring, and a schedule that fits your life. Here is exactly how to do it.
Read guide →
Autolyse: Why 30 Minutes of Waiting Improves Your Bread
Autolyse is one of the simplest steps you can add to your bread baking routine, and it rewards you with better texture, easier handling, and more developed flavor. Here is how and why it works.
Read guide →Bulk Fermentation: Why Temperature Changes Everything
Your bulk fermentation timeline is not set in stone. Temperature is the hidden variable that controls how fast your dough ferments, how sour it gets, and whether your bread turns out great or disappointing.
Read guide →
Bulk Fermentation: The Most Important Step in Sourdough
Bulk fermentation is where your sourdough develops flavor, structure, and character. Learn how to judge timing by feel, not just the clock, and avoid the most common mistakes.
Read guide →Understanding Baker's Percentages and Hydration
Baker's percentages are the universal language of bread baking. Learn what hydration means, how to calculate it, and why it's the key to consistent results.
Read guide →
Sourdough Hydration Explained: What the Numbers Actually Mean
Confused by hydration percentages? This plain-English guide explains what sourdough hydration means, how it affects your bread, and what level is right for you.
Read guide →New guides on Fermentation Science are added regularly and appear here automatically as soon as they go live.
Frequently asked questions
How does dough temperature actually change fermentation time?
Fermentation roughly doubles or halves for every 10°F change in dough temperature — a dough that bulk ferments in 5 hours at 75°F might take closer to 10 hours at 65°F. This is why tracking dough temperature, not just ambient room temperature, gives far more consistent results.
What does hydration percentage actually mean, and why does it matter?
Hydration is the weight of water as a percentage of flour weight — a 75% hydration dough has 750g water per 1000g flour. Higher hydration (80%+) produces a more open, irregular crumb but is stickier and harder to shape; lower hydration (65-70%) is easier to handle but denser.
What's the point of autolyse if I'm going to knead or fold anyway?
Autolyse — resting flour and water together for 20 to 60 minutes before adding starter and salt — lets flour fully hydrate and enzymes begin breaking down starches, which reduces the mixing time needed to develop gluten afterward. It particularly helps with whole grain flours that absorb water more slowly.
How do baker's percentages help when scaling a recipe?
Baker's percentages express every ingredient as a percentage of total flour weight (which is always 100%), making it straightforward to scale a recipe up or down while keeping identical ratios. A recipe at 75% hydration and 2% salt stays the same recipe whether you're using 500g or 2kg of flour.
Does the float test actually prove a starter is ready to bake with?
A spoonful of active starter floating in water suggests good gas production, but it's not fully reliable — some perfectly good starters sink due to their specific flour or hydration, and some risen starters float from trapped air rather than true fermentation strength. Watching for consistent doubling within 4-8 hours is a more reliable indicator.
Why do professional recipes give ingredient weights instead of cups?
A cup of flour can vary by 20% or more in actual weight depending on how it's scooped and packed, which throws off hydration ratios enough to change dough behavior noticeably. Weighing ingredients on a scale accurate to 1 gram removes this variability entirely.