A tall sourdough boule with a blistered amber crust and raised ears, resting on a wooden board.

The Opinionated Baker's Bread Lab

The Sourdough Formula

The book teaches you how to think like a sourdough baker.The app helps you work like one.

One system, two tools

The book teaches the thinking. The app builds the practice.

The book explains how I learned what I know, so you can understand how I think when I bake. The app helps you put that reasoning to work, bake after bake. It helps you plan, calculate, and make decisions, then preserves what you planned, what actually happened, and what the finished bread revealed.

Every bread you log makes the next one better.

A Word on the Word “Opinionated”

I know. “Opinionated” evokes negative reactions, so let me start by explaining what I mean.

“…in this book being opinionated simply means I cut through the over-choice of the blank slate.”

Drawing on decades of successes and failures, I’ll tell you exactly where you should start. At every step, I’ll point you toward the concepts you need to master so you can focus on what really matters.

— From “Foreword — A Word on the Word ‘Opinionated,’” in The Sourdough Formula
A close view of a tall sourdough boule opening dramatically along its scored crust.
Thick slices of sourdough on a walnut board, one spread with butter and drizzled with honey, beside a cellar of flake salt, a jar of chili crisp, a pat of butter, and a bread knife.

There is no food product you can make yourself at home that is more worthy of the effort than bread.

This is especially true of sourdough bread. It is nearly impossible to buy it as good as you will learn to make yourself, and most commercial bread (especially sourdough, the sour taste of which is often artificially achieved by the addition of vinegar) will eventually seem not worth eating by comparison. More importantly, the simplicity of combining three basic ingredients and producing a beautiful and delicious loaf feels nothing less than magical, and your sense of accomplishment at this alchemy will be intoxicating and addicting. In addition to the complete control over ingredients and methods, you have the additional luxury of using time to create flavor, and you’ll soon learn that patience tastes good.

— From The Sourdough Formula

It's a Formula, Not a Recipe.

A recipe is often a formal expression of instinct. If you’re cooking dinner for two, you can take a chicken, add a pinch of salt, a small shake of tarragon, half a clove of garlic, a squeeze or two of whatever citrus fruit you have on hand, and whatever else feels right in the moment. The stakes are low, the quantities are small, and your senses and experience can guide you to a delicious result. But try scaling that same “recipe” to feed 50 people and the entire philosophy breaks down. You cannot meaningfully multiply “a pinch” of salt or a “squeeze” of lemon by 50. Suddenly you need exact quantities, repeatable ratios, and real measurements because scale does not absorb or forgive mistakes—it amplifies and compounds them.

With bread, a small error multiplies until it becomes disastrous. A slightly vague hydration, a casual amount of starter, an imprecise salt percentage, or an unclear fermentation target may be survivable in one experimental loaf, but scale that confusion up and you have not created consistency. You have created a larger, more extensive (and expensive) failure.

This is why I distinguish so vehemently between recipe and formula. A recipe survives interpretation, but a formula is designed to survive scaling. Bread, especially lean hearth bread, is much closer to the world of sciences like chemistry and engineering than arts like painting and music, using formulas rather than recipes because the relationships between flour, water, salt, and fermentation must remain stable whether you’re making one loaf or one hundred. Sure, when baking on a commercial scale, some variables like water migration and heat retention change with the larger sized dough mass, and that affects things like fermentation rate (which is admittedly no minor thing). But for the most part, making one bread is the same as making dozens.

— From “The Baker’s Percentage (It’s a Formula, Not a Recipe!),” in The Sourdough Formula
A sourdough loaf cut open to reveal a translucent, irregular crumb beneath a dark, blistered crust.

Before, during, and after the bake

Plan. Bake. Troubleshoot. Learn.

  1. Plan

    Explore and plan everything the night before: choose the formula, build the levain, let the app run the math, set the schedule, and arm the reminders so you're ready to bake in the morning.

  2. Bake

    On bake day: follow the plan step by step from first mix to oven to cooling rack, keeping the timers and temperatures in view, and recording what actually happened in words, numbers, and photos along the way.

  3. Troubleshoot

    Get calm, situation-specific help when something looks or feels wrong. The app considers your formula, schedule, temperatures, timers, and observations, so its guidance is grounded in what actually happened, not generic advice or guesswork.

  4. Learn

    Every bake becomes the baseline for the next one: formulas, photos, and outcomes can be reviewed and compared to your entire bake history, so what you learn today is there when you need it tomorrow.

So this is me, presenting a system. My system. The result of decades of baking, experimentation, failure, refinement, and study. I will ask you to trust my opinions, secure in the knowledge that I have tried many approaches over the years. While I include some variations throughout so you can have a little pick-your-own-adventure fun from time to time, the entire system rests on a single underlying philosophy, one I hope you’ll find both practical and compelling:

A halved sourdough loaf photographed from above, showing an open, lacy crumb.

“You don’t need to be a talented cook or experienced baker to make exceptional bread.”

Anyone can do it. I promise. You don’t need mystical intuition, specialized equipment, or expensive ingredients. Some of the best breads I’ve made cost about $1.50 in ingredients and could easily fetch 10 times that or more at market. What you will need is a fundamental understanding of these three things: simple formulas you can memorize so you never need a recipe again, careful observations recorded against repeatable techniques, and the willingness to learn what’s actually happening inside the dough, so you can make the fine adjustments needed to carry you from good to exceptional bread.

— From “Foreword — A Word on the Word ‘Opinionated,’” in The Sourdough Formula

Explore the project

The system and the baker behind it.

Front cover of The Op!nionated Baker’s Sourdough Formula by Danny Kosarin: a golden sourdough boule on a wooden board against deep slate, with the subtitle “What Everyone Gets Wrong About Sourdough Bread … and Why It’s Not a Recipe!” and the loaf’s formula in the corner.

The System

One system, two tools: the book that teaches the thinking and the app that builds the practice.

Danny Kosarin, The Opinionated Baker, in a dark blue shirt, smiling.

The Baker

The point of view behind the work: who I am, why you can trust the opinions, and how to reach me.