“Leavening (baking soda and/or calcium phosphate)” refers to a chemical leavening system comprising a base (sodium bicarbonate, NaHCO₃) and a food-grade acid (here, acidic calcium phosphate). Upon hydration and/or heating, the acid–base reaction releases carbon dioxide (CO₂), forming gas cells that expand the batter/dough and deliver rise and tenderness. Calcium phosphate acids act as fast (cold-acting) or moderate acids and are often combined in “double-acting” baking powders to provide CO₂ both at mix and in the oven.

Calories (energy value)
0 kcal per 100 g (inorganic salts; no metabolizable energy).

Composition and mechanism

• Base: NaHCO₃ raises pH, supports Maillard browning, and contributes to a golden crust; excess causes soapy/alkaline off-taste.

• Acid: Calcium phosphates (MCP, DCP) supply protons (H⁺) to neutralize bicarbonate and generate CO₂, nudging final pH toward neutral.

• Key reactions (simplified):

  • NaHCO₃ + H⁺ → Na⁺ + CO₂↑ + H₂O

  • Thermal decomposition if base remains: 2 NaHCO₃ → Na₂CO₃ + CO₂↑ + H₂O (> ~80–90 °C)

• Gas yield: 1 g NaHCO₃ → ~0.266 L CO₂ at STP (≈266 mL) when fully neutralized (1 mol : 1 mol).

Process and sensory parameters

• Reaction rate: MCP reacts on hydration (cold-acting); some CO₂ can evolve during baking depending on acid profile and other recipe acids.

• pH and color: a balanced acid:base ratio targets pH ~6.8–7.4 in batter; higher pH → more browning but risk of alkaline taste.

• Moisture: activation starts with water—mix and bake promptly to avoid gas loss in fast systems.

Formats

• Straight baking soda: use only if the recipe provides natural acids (buttermilk, yogurt, natural cocoa, honey, lemon juice).

• Baking powder: pre-balanced blend of NaHCO₃ + acid (here, calcium phosphate) + anticaking starch. Often double-acting with a fast (MCP) and a slow/thermal component.

Indicative use levels (food)

• Baking soda: ~0.5–1.0% of flour weight when sufficient acid is present in the formula.

• Baking powder (NaHCO₃ + calcium phosphate): 2–4% of flour weight in most home baking.

• Neutralization: each 1 g NaHCO₃ requires stoichiometric acid equivalents; required grams depend on acid type and moisture.

Calcium phosphate characteristics

• Monocalcium phosphate (MCP, E341(i)): strong/fast acid, releases CO₂ immediately on hydration—ideal for quick mixes (pancakes, muffins).

• Dicalcium phosphate (DCP, E341(ii)): milder acid, gradual CO₂ release and pH buffering; often paired with MCP or other acids.

• They may modestly contribute Ca²⁺ and structural strength, but their primary role is acidification for leavening.

Quality and physical properties

• Appearance: fine, white, odorless powders.

• Solubility: baking soda highly water-soluble; acidic calcium phosphates sparingly to moderately soluble, sufficient to react in batter.

• Hygroscopicity: moderate—protect from moisture (tight packaging, desiccants).

Safety and regulatory

• Regulatory status (EU/US): E500 (sodium carbonates) and E341 (calcium phosphates) are GRAS at normal use levels.

• Allergenicity: none typical; consider sodium load from NaHCO₃ for restricted-sodium diets.

• Cosmetic cross-use: baking soda appears in effervescent bath products (with citric acid) and as a pH adjuster; calcium phosphates see limited cosmetic use (more common in oral care). No calories contributed.

Storage and shelf life

• Store cool, dry, airtight.

• Baking powder loses strength if exposed to humidity; check activity via a warm-water test (immediate effervescence).

• Typical shelf life: 12–24 months when properly stored.

Troubleshooting (baked goods)

• Soapy/alkaline taste, greenish crumb → excess soda or insufficient acid: reduce NaHCO₃ or increase acid (MCP or natural recipe acids).

• Low volume / tight crumb → too little leavener or pH too low suppressing Maillard: raise leavener slightly or rebalance acid:base.

• Tunneling (large channels) → gas release too rapid (too much MCP/high moisture) or overmixing: reduce fast acid, mix gently, bake promptly.

• Pale crust → pH too low or low sugars: rebalance neutralization; allow a touch of free soda for browning (avoid off-taste).

Formulation notes

• Buttermilk/yogurt/honey formulas: baking soda alone may suffice, but a small MCP addition improves pH stability and volume.

• Quick breads: prefer double-acting systems (MCP + a slower acid) for tolerance to bench time and oven spring.

• Sodium reduction: replace part of NaHCO₃ with potassium bicarbonate; recalculate the acid (calcium phosphate) and check flavor.

Conclusion
A baking soda and/or calcium phosphate system is a reliable, tunable chemical leavener: baking soda supplies gas potential and drives browning; calcium phosphates neutralize and shape the CO₂-release kinetics, stabilizing pH and crumb quality. Correct stoichiometry, moisture control, and process timing ensure consistent rise, texture, and flavor, with the leavening agents themselves contributing 0 kcal.