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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Organic AcidsFlavor ProfileSournessGlycemic Index

Abby Johnston

Post-Antibiotic Recovery: Rebuilding the Microbiome with Fibre Diversity

A course of broad-spectrum antibiotics is like a forest fire. It burns down the infection, but it also incinerates the "old growth forest" of your beneficial microbiome. Species like Bifidobacterium and Lactobacillus are often collateral damage.

The Retrograde Method: Freezing and Toasting for Maximum Prebiotics

This guide details The Retrograde Method—a specific protocol of cooling, freezing, and toasting designed to manipulate starch crystals. It turns a standard slice of sourdough into a high-performance delivery system for Resistant Starch (Type 3).

Stress Baking Psychology: Mindfulness and Tactile Therapy

"Stress baking" is often dismissed as a quirky coping mechanism or procrastination. But psychologists and occupational therapists view it differently. They see it as a legitimate form of sensory regulation.

Bioavailability: How Acidity Neutralises Phytic Acid to Unlock Iron & Zinc

In raw grains, minerals are locked away behind a chemical defence mechanism designed to prevent digestion. This lock is called Phytic Acid (or phytate). Unless you have the key to open it, you are likely excreting the vast majority of the nutrition you think you are eating.

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.

Troubleshoot: The "Fool's Crumb"

In the pursuit of the "Instagram Crumb"—that wild, open lattice of air pockets—many bakers fall into a specific trap. You slice the loaf and see massive, cavernous holes. You celebrate. But when you eat it, the bread is heavy, chewy, and dense.

Scoring Mechanics: Functional Expansion vs. Decorative Art

Scoring is the act of creating a controlled weakness in the "skin" of the loaf. Without it, the massive pressure of oven spring will find its own way out, usually rupturing the loaf in an ugly "blowout" at the bottom [1]. There are two types of cuts: Functional and Decorative.

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.

Milk: The Chemical Softener

Water is neutral. Milk is complex. By swapping water for milk (as in Shokupan or Sandwich Bread), you introduce three new variables: Fat, Protein (Casein), and Sugar (Lactose).

Butter: The Gluten Lubricant

Butter is the bridge between bread and pastry. In small amounts, it softens. In large amounts (like Brioche), it transforms the dough into a foam-like structure that is more air than wheat.

Rice Flour: The Non-Stick Shield

Rice flour is the one flour in your arsenal that should never go inside your wheat dough (unless you are baking gluten-free). Its role is purely external. It is the mechanic’s glove.

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.

Gas Retention: Why Weak Gluten Networks Leak CO2

You can have the most active starter in the world, pumping out massive amounts of Carbon Dioxide (CO2). But if your dough cannot trap that gas, your bread will be a brick. This is the principle of Gas Retention.

Thermal Death Curves: What Happens at 60°C?

When you slide a loaf into a 250°C oven, you are subjecting the microbial city inside to a rapid climate change. For the first few minutes, the yeast and bacteria actually work faster (the "Oven Spring"). But as the internal temperature rises, they hit a wall. This is the Thermal Death Curve.

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.

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

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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 |