What Is GAD (Glutamate Decarboxylase)?

The Glossary

18 Jan

The Definition

GAD (Glutamate Decarboxylase) is an enzyme produced by certain strains of Lactic Acid Bacteria (such as L. brevis) within a sourdough starter. It facilitates the conversion of glutamate—an amino acid abundant in wheat—into GABA (Gamma-aminobutyric acid), a neurotransmitter associated with reducing anxiety and stress.

The Science: The Thermal Switch

GAD activity is highly temperature-dependent. Research indicates that to maximise GAD activity (and thus GABA content in bread), fermentation should occur at warmer temperatures (30–35°C), rather than the cold temperatures used for retarding [1].

References

Diana, M., Quílez, J., & Rafecas, M. (2014). Sourdough bread enriched with aminobutyric acid (GABA). Journal of Cereal Science.

Last updated: 6 January, 2026

Featured

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Pre-shaping is an intermediate step between bulk fermentation and final shaping. The dough is divided and loosely formed into rounds, then left to rest (bench rest) for 15–30 minutes. This step reorganises the gluten network after the division and creates a smooth "skin" on the dough.

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Refined Flour (often labelled as White Bread Flour) has had the bran and germ mechanically removed, leaving only the starchy endosperm. While this creates a flour that produces high volume and airy bread (due to strong, uninterrupted gluten), it is a biological "desert."

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Hooch is a colloquial term for the liquid layer (ranging from clear to grey or black) that accumulates on top of a neglected sourdough starter. Biologically, it is primarily ethanol (alcohol) produced by wild yeast during fermentation.

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Sourdough HealthNeurotransmittersGABAAdvanced Fermentation

The Pact

Leaky Gut Protocols: Butyrate Production and Lining Repair

The term "Leaky Gut" (Increased Intestinal Permeability) was once dismissed by conventional medicine. Today, it is a recognised driver of systemic inflammation, autoimmunity, and food sensitivities.

FODMAPs & Fermentation: Navigating IBS and the 48h Degradation Curve

When you mix flour and water and let it sit, a war for resources begins. The bacteria hunt for fuel. If given enough time, they will consume the fructans, effectively "pre-digesting" the bread before it ever reaches your plate.

Gut-Skin Axis: Sourdough, Systemic Inflammation, and Acne

This is the story of the Gut-Skin Axis: the direct line of communication between what you eat, your insulin levels, and the clarity of your skin. And it explains why sourdough might be the dermatological intervention you didn't know you needed.

Ghost Probiotics: Why Dead Bacteria Still Talk

If you view probiotics solely as "live microorganisms," then sourdough is a barren wasteland. It is sterile. But emerging research into the gut-brain axis suggests something profound: bacteria do not need to be alive to speak to your body.

The Temperature Switch: Baking for GABA

The key molecule here is GABA (gamma-aminobutyric acid). It is the brain's primary inhibitory neurotransmitter, the biological "off switch" for stress and anxiety. And to maximise it in your bread, you may need to turn up the heat.

The Oxytocin Loop: Baking as Social Biology

When you break bread, is the feeling of connection purely emotional, or is it chemical? New research into Lactobacillus reuteri—the "Love Bug" sometimes found in sourdough—suggests these microbes may trigger the release of oxytocin, the "cuddle hormone," to encourage sharing and trust.

Explore the "Oxytocin Loop": the evolutionary theory that suggests baking isn't just feeding the body, but chemically engineering bonding.

The Calorie Paradox in Sourdough: Why Not All Calories Are Created Equal

The "Calorie Paradox" of sourdough is that the energy listed on the label is not necessarily the energy your body absorbs. By the time the wild yeast and lactic acid bacteria have finished with the flour, they have fundamentally altered its structure. They have changed the math.

The Glucose Curve: Sourdough and Diabetes

Sourdough offers a metabolic loophole. By enlisting microbes to pre-digest our grain and acidify the dough, we can enjoy the ritual of bread without the metabolic penalty of a sugar crash. It is not just about lower carbs; it is about slower chemistry.

The "Sourfaux" Guide: How to Spot Sourdough Fakes

True sourdough is the result of a biological pact: a slow fermentation of flour and water by wild yeast and lactic acid bacteria. This process takes time—often 24 to 48 hours—to break down gluten, neutralise phytates, and develop complex organic acids.

"Sourfaux," a term coined by the Real Bread Campaign [1], refers to bread that mimics the taste of sourdough without the time or the biological benefits [1]. It is fast food dressed up as slow food.

The Gluten Free Loophole

Sourdough is not defined by wheat. Sourdough is a technology. It is the biological protocol of using microbes to unlock the nutrition of a seed. And here is the loophole: The pact applies to every seed.

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 Peacemaker: Levilactobacillus brevis

While other microbes are busy fighting for sugar, L. brevis is quietly performing a chemical conversion that has profound implications for the human brain. It takes Glutamate—an excitatory molecule—and transforms it into GABA, the molecule of calm.

The Dead Starter: Pathogen Takeover in Neglected Jars

There is a point of no return. A moment when a neglected starter stops being a culture of beneficial microbes and becomes a Petri dish for pathogens. This transition is chemical. It is driven by a single variable: pH.

Microbial Ecology: The Lifecycle of Your Starter (And Why It Smells)

When you mix flour and water for the first time, you are not just making dough; you are terraforming a new world. You are initiating a biological sequence known as Ecological Succession. This process is violent, chaotic, and predictable. It involves a war for resources, a "Great Extinction" event, and finally, the establishment of a stable civilization.

The Handshake: The Baker's Skin Microbiome

Your hands are not sterile tools. They are a thriving ecosystem, a landscape of ridges and valleys populated by millions of bacterial residents. When you knead a loaf, you are not just shaping structure; you are performing a biological handshake. You are introducing your own microbial signature to the dough.

Meet Your Baker: F. sanfranciscensis.

Meet the rod-shaped bacterium with a name that barely fits on a label: Fructilactobacillus sanfranciscensis. This organism is the engine of the sourdough ecosystem. And its history is stranger than you think.

The Starter Invaders: Mold, Kahm, and Pink Streaks

When you open your jar to find fuzzy islands, wrinkled skins, or neon streaks, it is a sign that the pact has been broken. The acid was not strong enough, or the invader was too resilient.

The Sourdough Ash Ratio

When you feed your starter exclusively with white bread flour, you are effectively putting your microbial colony on a diet of pure sugar while denying them the vitamins they need to metabolise it. You are creating a starter that is energy-rich but nutrient-poor.

Rye Flour: The Enzymatic Supercharger

Water is not just a filler; it is the trigger. Flour in a bag is biologically dormant. It is only when water is introduced that the enzymes (amylase and protease) wake up and the biological clock begins to tick.

Diastatic Malt: The Fuel Injector

Professional bakers have a secret weapon for achieving that dark, mahogany crust and open interior: Malt. But not all malt is created equal. You must distinguish between "Diastatic" (Active) and "Non-Diastatic" (Inactive).

Spelt Flour: The Extensibility Paradox

Spelt is the ancient cousin of modern wheat. Many bakers switch to it for its nutty flavour or perceived health benefits, but they are often shocked when their dough collapses into a puddle.

Chlorine: The Silent Killer

If you are doing everything right but your starter refuses to rise, look at your tap. Municipal water treatment is a triumph of public health, designed to kill bacteria. Your sourdough starter is bacteria.

Salt: The Osmotic Brake

In the culinary world, salt is a seasoning. It makes food taste "more like itself." In the biological world of sourdough, salt is a weapon. It is the primary control mechanism you have to regulate the speed, strength, and safety of your fermentation.

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.

Viscoelasticity: Extensibility vs. Elasticity (Rheology)

Dough is a contradiction. It is a solid that flows like a liquid. In physics, this property is called Viscoelasticity. It means the material has both viscous (flow) and elastic (snap-back) characteristics.

Thermodynamics: Radiant vs. Conductive Heat (Dutch Oven Physics)

When you open your home oven door to load the bread, the air temperature drops by 50°C or more. A thin baking tray loses heat instantly. A preheated Dutch oven does not. It acts as a thermal battery, maintaining a stable 250°C environment even when the oven air cools down.

Water Activity (Aw): The Secret to Sourdough's Shelf Life

If you leave a slice of supermarket white bread on the counter, it will turn into a brick in 24 hours. If you leave it in a bag, it will grow blue fuzz in 3 days. But a loaf of sourdough, sitting cut-side down on a wooden board, behaves differently. It doesn't mould. It doesn't dry out instantly. It simply... ages.

What Is GAD (Glutamate Decarboxylase)?

The Definition

The Science: The Thermal Switch

References

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 GAD (Glutamate Decarboxylase)?

The Definition

The Science: The Thermal Switch

References

What Is Oven Spring?

What Is Gluten?

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 |