What Is Acetic Acid?

The Glossary

4 Feb

The Definition

Acetic acid is an organic acid produced by heterofermentative bacteria (like F. sanfranciscensis) alongside lactic acid, ethanol, and CO₂. It is responsible for the sharp, vinegary "tang" associated with San Francisco-style sourdough. Beyond flavour, it is a powerful antifungal agent.

The Flavour Profile

Acetic acid production is favoured by cooler temperatures and stiffer (lower hydration) starters. It has a significant impact on blood sugar regulation, as acetic acid is linked to delayed gastric emptying, which lowers the bread’s Glycaemic Index (GI) [1].

References

Liljeberg, H., & Björck, I. (1998). Delayed gastric emptying rate may explain improved glycaemia in healthy subjects to a starchy meal with added vinegar. European Journal of Clinical Nutrition.

Last updated: 6 January, 2026

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Mar 17, 2026

Bassinage is an advanced mixing technique that involves holding back a significant portion of the water (typically 10–20%) from the initial mix and adding it slowly after the gluten network has already been developed. It is the secret weapon used to achieve modern "open crumb" sourdough (like Pan de Cristal).

Mar 17, 2026

Mar 17, 2026

Hydration Percentage in baking is a calculation that represents the ratio of water to flour in a recipe by weight. In sourdough, it is the primary variable controlling crumb openness.

Mar 17, 2026

Feb 14, 2026

Maltose is a disaccharide (simple sugar) produced when amylase enzymes break down the starch in flour. It is the primary fuel source for the sourdough ecosystem. Uniquely, the bacterium F. sanfranciscensis prefers maltose over glucose, giving it a competitive advantage in wheat dough.

Feb 14, 2026

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Abby Johnston

Weight Loss & Satiety: The Density Analysis of Sourdough vs. Commercial Bread

Commercial bread requires almost no chewing, dissolves instantly in the stomach, and leaves you hungry again within an hour. But sourdough is a different material entirely. It is dense. It is structured. And crucially, it is acidic.

The Second Brain: How Intestinal Microbes Influence Mood

There is a second nervous system in your body, one so complex and autonomous that scientists call it "The Second Brain." It is located not in your skull, but in your gut. This represents the Enteric Nervous System (ENS). And it doesn't just digest food. It manufactures the chemistry of your mood.

Non-Celiac Gluten Sensitivity: Is it the Gluten or the Fructans?

Because wheat contains both gluten and fructans, it is easy to confuse the two. When you stop eating bread, you eliminate both. You feel better. You blame the gluten. But you may have simply lowered your FODMAP load.

The Morning Toast Protocol: For Cortisol Management

Spiking your blood sugar with sweet carbs triggers a subsequent crash (reactive hypoglycaemia), which forces your body to release Cortisol and Adrenaline to bring levels back up. You are literally chemically inducing stress before 10 AM.

Meet The Yeast: The Sprinter vs. The Marathon Runner

In the world of baking, the word "yeast" is used carelessly. We treat the beige granules in a packet and the wild population in a sourdough starter as if they are the same organism just living at different speeds. They are not.

Sugar Hunters: How Amylase Unlocks the Grain

Microbes are hungry. To survive, they need sugar. But flour is not sugar. It is starch—long, complex chains of glucose molecules locked together in granules. For a yeast cell, a starch granule is like a boulder. It is too big to eat. Before the yeast can feast, someone has to break the rock. This is the job of Amylase.

The Invisible War: Phages

You can see mold. You can smell kahm yeast. But the most lethal predator in your sourdough starter is entirely invisible. They are Bacteriophages (or simply "Phages"). They are viruses that hunt bacteria. And in the dense microbial city of a sourdough culture, they are the apex predators.

The Survivor: Lactobacillus plantarum

Lactobacillus plantarum is a survivor. It is the "Navy SEAL" of the lactic acid bacteria. It is found everywhere: in sauerkraut, pickles, kimchi, olive brines, and—crucially—in the most robust sourdough starters.

The "Scrapings" Method: Zero Waste Maintenance

Standard sourdough maintenance protocols are inherently wasteful. The classic "1:1:1" feeding ratio—where you discard half your starter to feed the rest—is a relic of a time when flour was cheap and understanding of microbiology was poor. Over the course of a year, a conscientious home baker following these rules will throw away kilograms of high-quality grain.

Tactile Metrics: The Windowpane, The Poke, The Jiggly Test

The only reliable clock is the dough itself. To read it, you must stop looking and start touching. These are the three Tactile Metrics that every sourdough baker must master to judge the invisible biology of the jar.

The Ultimate Guide to Autolyse

In the rush to get bread into the oven, many home bakers skip the first, most critical step of the process.

They mix everything at once—flour, water, starter, salt—and then wonder why their dough fights them. Why it tears when they stretch it. Why the crumb is tight. The missing variable is Autolyse.

Troubleshoot: Gummy Crumb

There is a specific heartbreak reserved for the moment you slice a beautiful loaf, only to find the knife coated in a sticky, shiny residue. The crumb looks wet. When you press it, it balls up like putty rather than springing back. It eats like raw dough.

Olive Oil: The Lipid Softener

Sourdough is traditionally lean (Flour, Water, Salt). When you introduce a lipid like Extra Virgin Olive Oil, you are entering the territory of "Enriched Dough." You are trading some crust crispness for crumb tenderness.

Whole Wheat: The Thirsty Substrate

White flour is a fuel source; Whole Wheat is a meal. By including the bran (the outer shell) and the germ (the embryo), you introduce a complex array of minerals and fibres that fundamentally change the physics of the dough.

Seeds: The Hydration Thieves

Seeds are not passive additions to bread. They are biologically active sponges. If you throw raw seeds into your dough, they will compete with the gluten for water, often winning the war and leaving you with a dry, tight loaf.

Altitude Baking: Adjusting Pressure Variables

At high altitudes, the air pressure is lower. This invisible change alters the behaviour of every gas bubble and water molecule in your dough. To bake successfully, you must adjust your variables to match your environment.

The Ear: The Physics of Differential Expansion

The ear is more than decoration. It is functional physics. It is the visual proof that your loaf expanded to its maximum potential before the crust hardened. To get an ear, you must master the forces of Tension and Differential Expansion.

The Physics of Steam: Why Moisture Creates a Crispier Crust

It seems like a contradiction. If you want a dry, crispy crust, why would you flood your oven with water? Yet, every professional baker knows that steam is the secret ingredient. A loaf baked in a dry oven will be dull, dense, and grey. A loaf baked in steam will be glossy, voluminous, and shatteringly crisp.

pH Dynamics: Charting the Drop from 6.0 to 3.5

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.

What Is Acetic Acid?

The Definition

The Flavour Profile

References

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The Pact: Sourdough Protocols

Explore the science

The Body

The Microbes

The Method

The Ingredients

The Chemistry

Join The Resistance.

They Bake for Aesthetics. We bake for biology 💁‍♀️.

CITIZEN SCIENCE FOR STEWARDS OF SOURDOUGH

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CITIZEN SCIENCE FOR STEWARDS OF SOURDOUGH |

The Pact

The Protocol

The Science

The Glossary

The Resistance

What Is Acetic Acid?

The Definition

The Flavour Profile

References

Seeds: The Hydration Thieves

Water: The Invisible Variable

Get the app

The Pact: Sourdough Protocols

Explore the science

The Body

The Microbes

The Method

The Ingredients

The Chemistry

Join The Resistance.

They Bake for Aesthetics. We bake for biology 💁‍♀️.

CITIZEN SCIENCE FOR STEWARDS OF SOURDOUGH

|

CITIZEN SCIENCE FOR STEWARDS OF SOURDOUGH | CITIZEN SCIENCE FOR STEWARDS OF SOURDOUGH |

The Pact

The Protocol

The Science

The Glossary

The Resistance

CITIZEN SCIENCE FOR STEWARDS OF SOURDOUGH |