By Dr. Alyaa Homoud, Head of Market Development (Flour & Baking), REDA Bake
Leavening agents, either biological, chemical, or steam, are essential components in baking.
Leavening agents introduce gases into doughs and batters, improving volume, texture, and overall structure. These agents are categorized into biological, chemical, and steam-based types, each functioning through distinct mechanisms to create aeration (Gélinas, 2022).
1. Biological leavening agents
Biological leavening involves microorganisms that generate gases as metabolic byproducts, enhancing dough rise and contributing to flavor (Neeharika, Suneetha and Kumari, 2020).
Yeast fermentation
The most common biological leavening agent is Saccharomyces cerevisiae (baker’s yeast), which metabolizes fermentable sugars through glycolysis, leading to the production of carbon dioxide (CO2) and ethanol via alcoholic fermentation (Liu et al., 2021):
+ Mechanism: CO2 gets trapped within the gluten network, expanding the dough and creating a soft, airy texture.
+ Optimal conditions: Yeast thrives best at 25–35°C and a pH of 4.5 to 6.0 (Gélinas, 2022).
+ Factors affecting yeast activity:
– Sugar concentration: While yeast requires sugar for fermentation, high sugar levels cause osmotic stress, inhibiting yeast activity.
– Salt concentration: Excess salt can retard fermentation by dehydrating yeast cells.
– Hydration levels: Proper moisture content is crucial for yeast viability and gas production (Liu et al., 2021).
Sourdough fermentation
Sourdough involves a symbiotic relationship between yeast and lactic acid bacteria (LAB), primarily a species of Lactobacillus. LAB produce lactic and acetic acids, influencing dough acidity, taste, and texture (Cobbold, 2018):
+ Acidic environment: LAB lowers the dough’s pH, extending shelf life and enhancing gluten strength.
+ Flavor development: Acetic acid imparts tangy notes, while lactic acid provides a mild sourness (Lee, 2020).
Sourdough fermentation produces a more complex flavor and longer shelf life compared to conventional yeast-leavened bread.
2. Chemical leavening agents
Chemical leaveners rely on acid-base reactions to generate CO2 gas quickly, making them suitable for rapid baking applications like cakes, muffins, and quick breads (Gélinas, 2022).
Baking soda (sodium bicarbonate)
Sodium bicarbonate (NaHCO3) releases CO2 when it reacts with acids. A common reaction with acetic acid (vinegar) is (Liu et al., 2021):
+ Without acid: If used alone, sodium bicarbonate can decompose into sodium carbonate (Na2CO3), which imparts a bitter, soapy taste.
+ Acid sources: Common acids paired with baking soda include lemon juice (citric acid), yogurt (lactic acid), and cream of tartar (potassium bitartrate) (Gélinas, 2022).
Dr. Alyaa Homoud, REDA Bake
Baking powder
Baking powder is a pre-mixed leavening system consisting of:
+ Sodium bicarbonate
+ Acid salts (e.g., monocalcium phosphate, sodium aluminum sulfate)
+ Starch (acts as a moisture absorber to prevent premature reactions) (Neeharika, Suneetha and Kumari, 2020).
Double-acting baking powder
+ First CO2 release: Upon mixing with liquid.
+ Second CO2 release: During baking due to heat activation (Gélinas, 2022).
This controlled gas release ensures a steady rise, making baking powder a staple for cakes and cookies.
3. Steam as a leavening agent
Steam functions as a physical leavening agent by utilizing water vaporization at high temperatures (Lee, 2020).
Mechanism of steam leavening
1. Water in the dough reaches boiling point (100°C).
2. Expanding steam increases pressure, pushing against the dough matrix.
3. Protein coagulation and starch gelatinization stabilize the expanded structure (Cobbold, 2018).
Applications of steam leavening
+ Choux pastry (profiteroles, éclairs): High water and egg content allow steam to create large, hollow structures.
+ Puff pastry: Alternating layers of dough and fat trap steam, causing flaky texture formation.
+ Yorkshire pudding and popovers: The batter’s high moisture content leads to dramatic expansion (Lee, 2020).
Unlike yeast and chemical leaveners, steam is instantaneous and does not rely on fermentation or acid-base reactions.
Author
Based in Jiddah, Makkah, Saudi Arabia, Dr. Alyaa Homoud obtained her P.h.D. degree in Food Science and Technology at the Heriot-Watt University, in Edinburgh, Scotland (2015). She is Head of Market Development (Flour & Baking) at REDA Bake, a manufacturer of a variety of specialty bakery ingredients for commercial baking operations.
At REDA Bake, food quality and safety are Dr. Homoud’s priorities. With expertise in food science, baking, and technology, she optimizes manufacturing processes and uses data analysis to enhance consumer health. The company operates regionally across the Gulf, North Africa, Levant, Sub-Saharan Africa, South Africa, South Asia, Central Asia, South-East Asia, and China.
She had a consulting role in a Vision 2030 project, focusing on sustainability practices and innovation, and advising on the implementation of cutting-edge food technologies.
References
– Gélinas, P. (2022) ‘Gas sources in chemical leavening and other baker’s yeast substitutes: lessons from patents and science’. International Journal of Food Science. Available at.
– Neeharika, B., Suneetha, W. J. and Kumari, B. A. (2020) ‘Leavening agents for food industry’. ResearchGate. Available at.
– Liu, S., Song, J., Sun, M. and Sun, Y. (2021) ‘An Analysis of Acid-Base Reaction and Fermentation-Induced Leavening Agents in Bread Making’. UBC Library. Available at.
– Lee, G. J. (2020) ‘Change in height of breads baked by different type of leavening agents’. UBC Library. Available at.
– Cobbold, C. A. (2018) ‘The rise of alternative bread leavening technologies in the nineteenth century’. Taylor & Francis. Available at.
