The Science Behind Baking Soda and Sourdough Discard: Why It Gets Bubbly and Rises

If you’ve ever mixed sourdough discard with baking soda, you’ve probably noticed something fascinating—it immediately starts to bubble and expand. This transformation is not just magic; it’s science at work! Understanding why this happens will not only satisfy your curiosity but also help you make better use of sourdough discard in your baking.

What is Sourdough Starter Discard?

Sourdough discard is the portion of your sourdough starter that is removed during feedings to maintain a healthy and balanced culture. Unlike an active starter that is full of wild yeast and bubbling with fermentation, discard is less active because it hasn’t been recently fed. However, it still contains:

• Organic acids (such as lactic acid and acetic acid) that give sourdough its tangy flavor
• Enzymes and beneficial bacteria that contribute to texture and fermentation
• Residual wild yeast (though much less active than a fed starter)

Even though discard lacks strong leavening power on its own, it becomes incredibly useful when combined with baking soda.

The Science Behind Baking Soda and Sourdough Discard

Baking soda (sodium bicarbonate, NaHCO₃) is an alkaline compound that reacts with acids to produce carbon dioxide (CO₂) gas. Since sourdough discard is naturally acidic due to lactic and acetic acid, adding baking soda creates an instant reaction:

The Chemical Equation

Baking Soda (NaHCO₃) + Acid (H⁺) → Carbon Dioxide (CO₂) + Water (H₂O) + Salt

The carbon dioxide gas is what causes the discard mixture to bubble, rise, and become light and airy. This reaction is similar to what happens when you mix vinegar with baking soda—it creates an immediate fizzing effect due to the rapid release of gas.

Why Does Baking Soda Make the Discard Bubbly and Airy?

1️⃣ Acid-Base Reaction – The discard provides the acid needed to activate the baking soda, causing an immediate release of CO₂. The bubbles you see in your batter or dough are tiny pockets of trapped gas.

2️⃣ Instant Reaction – Unlike yeast fermentation, which takes hours, baking soda reacts the moment it comes into contact with acid. That’s why you see bubbles forming right away, and why baked goods using this reaction need to be cooked immediately.

3️⃣ Temporary Leavening – The CO₂ bubbles don’t last forever. If the batter sits too long, the gas will escape, leading to denser, flatter baked goods.

Why Are Discard Recipes Baked Right Away?

Timing is everything when using baking soda in sourdough discard recipes. Since the reaction is immediate and short-lived, baking the mixture right away ensures you trap the carbon dioxide inside the dough, creating a light, fluffy texture.

What Happens If You Wait Too Long?

⏳ The gas escapes – If the batter or dough sits out for too long, the CO₂ bubbles will dissipate, and the mixture will lose its rising power.
⏳ The dough can deflate – Without enough trapped gas, your baked goods may turn out dense, tough, or flat instead of light and airy.
⏳ Over-neutralization can occur – If too much baking soda is added or if it sits too long, the mixture may become overly alkaline, leading to an unpleasant soapy or metallic taste.

How to Prevent Deflation in Your Bakes

✅ Add baking soda last – If a recipe requires resting (like overnight waffles), mix in the baking soda right before cooking to ensure a fresh reaction.
✅ Bake immediately – The faster you get the batter into the oven, onto the griddle, or into the pan, the more lift you’ll retain.

Why Baking Soda is Preferred Over Baking Powder in Discard Recipes

Both baking soda and baking powder are leavening agents, but they work differently:

• Baking Soda requires an external acid (like sourdough discard) to react. The reaction happens all at once when mixed with acid.
• Baking Powder contains both a base (baking soda) and an acid (cream of tartar or other acids), making it self-activating. It releases gas in two stages—once when wet, and again when exposed to heat.

Because sourdough discard is already acidic, baking soda is the perfect choice to create instant leavening without the need for added acids.

Best Ways to Use Baking Soda in Sourdough Discard Recipes

The baking soda reaction works best in quick-bake recipes like:

✔️ Sourdough Discard Pancakes & Waffles – Baking soda gives them a light and fluffy texture. (Tip: Mix it in just before cooking for the best rise!)
✔️ Sourdough Discard Muffins & Cakes – The reaction boosts rise and tenderness.
✔️ Sourdough Crackers & Flatbreads – Baking soda can make them crispier by neutralizing some of the acids in the discard.
✔️ Sourdough Discard Biscuits – The gas bubbles create tender, flaky layers.

Additional Tips for Working with Baking Soda and Discard

📌 Use fresh baking soda – Baking soda loses potency over time. If it's older than 6 months, replace it for best results.

📌 Measure carefully – Too much baking soda can neutralize too much acid, leading to a bitter, soapy, or metallic aftertaste. A good rule of thumb is ¼ to ½ teaspoon per cup of discard.

📌 Consider the acidity of your discard – If your discard is very acidic (e.g., it's been sitting unfed for a long time), a little baking soda will mellow the tanginess while helping with leavening.

📌 Pair with other leaveners – Some discard recipes combine baking soda with yeast or baking powder for even more leavening power.

Final Thoughts

Mixing sourdough discard with baking soda is a simple yet effective way to repurpose discard while creating light, airy baked goods. The instant acid-base reaction makes this combination perfect for quick recipes that don’t require long fermentation.

✔️ Baking soda reacts with the natural acids in sourdough discard, releasing CO₂ bubbles.
✔️ The reaction happens immediately, so bake your batter right away to retain the airy texture.
✔️ If left too long, the bubbles will escape, and the mixture will lose its rising power.
✔️ Baking soda is a better choice than baking powder in discard recipes because discard is already acidic.
✔️ Use this reaction in pancakes, waffles, muffins, biscuits, and other quick-bake recipes for the best results.

By understanding the science behind this reaction, you can optimize your sourdough discard recipes and bake with confidence. Happy baking! 🥖✨