The Value Of Raising and Leavening in Baked Foods

The purpose of raising and leavening agents in baking is to create a light, airy texture in the finished product. Leavening agents are ingredients that cause the dough or batter to rise by releasing gases, such as carbon dioxide, which get trapped in the dough and create small air pockets. When the baked good is heated, the air pockets expand and the dough or batter rises, resulting in a fluffy, tender texture. Without them, most baked goods would produce flat, rather chewy foods. Many bakers fail to think about using leavening agents when they are producing bread and cookies and then try to work out why their cookies are so flat.

Typical raising agents can be grouped into three main types: these include the chemical agents such as baking powder and baking soda, the biological which is always yeast, and the physical sources such as steam and air. These are especially useful in producing light, airy textures in baked foods. 

Leavening Agents

Leavening is particularly important in bread-making, as it helps the dough to rise and gives the bread its characteristic texture and flavour. Yeast is a common leavening agent in bread-making, as it produces carbon dioxide gas during fermentation, which causes the bread dough to rise. Other leavening agents used in baking include baking powder and baking soda, which release carbon dioxide gas when they come into contact with acidic ingredients, such as buttermilk or vinegar.

Sodium Bicarbonate/Soda

One of the most important leavening agents is soda which is sodium bicarbonate. It is extremely benign as a food ingredient and to be treated as an ally in baking. Soda is bought at the grocers in the baking products aisle as a white crystalline powder. It has a molecular weight of 84.

Sodium bicarbonate is often used when the formulation already contains a certain amount of acid in its make-up. Brown sugar for example is acidic because it contains molasses which has an acidic pH.

Heat during the baking process will also encourage carbon dioxide formation which produces small gas bubbles causing the baking goods to rise.  When heated up to 50ºC, it starts to produce gas which produces the aerated texture in bread for example. By the time of reaching 100ºC, much of it has been converted to sodium carbonate. It is popular because it is so cheap, easily handled and harmless. It doesn’t have a flavour either and can be purchased extremely pure.

Baking powders used in Germany for example contain between 2.35 and 3.00 g of bound, effective carbon dioxide in the quantity determined for 500 g of flour. This occurs when carbon dioxide is the leavening gas. 

Baking Powder

Baking soda only contains a chemical leavening agent which is most often sodium bicarbonate. A baking powder on the other hand contains a leavening agent, a powdered acid with a neutral, inert buffer material.

The use of baking powder incorporates acid such as monocalcium phosphate, sodium aluminum phosphate and the sulphate version, or tartaric acid as well as sodium bicarbonate in some instances. The neutral buffer is another flour, usually cornstarch which serves as a bulking agent.

Potassium Bicarbonate

A leavening agent also used for low-sodium products. It is used as a total or partial replacement.

Ammonium Bicarbonate

 Ammonium bicarbonate breaks down on heating to release carbon dioxide and ammonia. There is no reaction with any leavening acid. Sodium bicarbonate leaves a residue  but ammonium bicarbonate does not when used in baking. There are no residual flavours from this salt. It does not affect the pH of bread and so no leavening acid is needed. It is not suitable for high moisture foods where the moisture content is over 5% w/w. Ammonia is soluble in water leaving an ammonia flavour which makes it inedible.

It is best used in low moisture foods such as dry bread, cookies, dry biscuits, wafers and crackers. No salts are produced either so it does not change the rheology of the dough. 

Novel Leavening Agents

 A solid polymorph of (+)-catechin with mucic acid or tartaric acid has been tried with the added benefit of incorporating polyphenols into the formulation. There was a general view these leavening agents could be incorporated into muffins (Carullo et al., 2020).

Pulque, which is a fermented white sap from Mexican agave has been tested with a wheat bread product. It was claimed that the increase in volume compared to the non-leavened control was about 50% v/v (Vernon-Carter et al., 2017). The fermented sap acts similarly to a sourdough starter culture. It’s not recognised yet as a potentially commercial alternative to other sourdough-like cultures.

Chickpea derived yeast is used in leavening. It is a traditional agent derived from the natural fermentation of ground chickpea in water. A ‘sweetdough’ is produced which alters the structure of the dough. It has a lower acidity than other types of sourdough.

Gas hydrates (GH) are formed when water and low molecular weight gases are subjected to low temperature and high pressure conditions. Suitable sized guest molecules are caged in hydrogen-bonded water molecules without chemical reactions to stabilize the structure (Srivasta et al., 2022; Fruhling et al., 2023). The cages are composed of pentagons and hexagons, depending on the gas molecule, forming one of three preferred structural forms (sI, sII, sH). In sI, the guest molecules are enclosed in cages of 12 pentagons (5¹²) or 12 pentagons and two hexagons (5¹² 6²). The most common hydrate structure is this latter form. Very small molecules (e.g. hydrogen) cannot, therefore, stabilize gas hydrates, while large molecules rather form larger cages (sII or sH).

In this case carbon dioxide for leavening as a gas is introduced into the dough or batter as a hydrate, a solid carrier material. Carbon dioxide has the E number 290 (E290). Unfortunately, it does not generate sufficient leavening or loosening as an aqueous solution or as dry ice. The stability of these solutions is lower than that of the CO2 hydrate.

Gas hydrates are added as particulates into the dough. The leavening agent is released through physically controlled decomposition. The main advantages over other leavening agents are many fold:-

• Only water and carbon dioxide are released as the hydrate breaks down.
• There are no flavour or texture changes in the final leavened product
• Gas release is in a few minutes compared to biological leavening.

The Neutralizing Value (NV)

The neutralizing value (NV) is the amount of leavening acid needed to react completely with a defined amount of baking soda. When all the leavening acid reacts with the soda, the pH will be very close to neutral which is ideal for baked foods of any sort.

Different leavening acids are available with different NVs. Those with a low NV must be used in greater amounts than those with a higher NV.

  The levels are:-

• sodium aluminium sulphate….104NV
• sodium aluminium phosphate…100NV
• anhydrous monocalcium phosphate…83NV
• monocalcium phosphate monohydrate…80NV
• sodium acid pyrophosphate….72-74NV
• cream of tartar…45NV
• glucono-delta-lactone…45-50NV
• dimagnesium phosphate….40NV
• dicalcium phosphate dehydrate…33NV

The quantity of CO₂ released during mixing depends on the rate of reaction (ROR). The leavening acids can be classified as fast-acting acids that dissolve rapidly during batter mixing, or as slow-acting acids (Ellinger, 1972). So choice of acid or its corresponding neutralization value is responsible for the timing of the release of carbon dioxide.

Leavening agents produce both a pre- and a post-leavening effect. Combinations of different acid carriers are frequently used so that the time of release can be precisely matched to the product.

When leavening acids such as monocalcium phosphate react with sodium bicarbonate they release between 60 and 70% of the total carbon dioxide. These are classified as nucleating or fast-acting leavening acids. Residual carbon dioxide gas is released thermally because it is an exothermic reaction which produces calcium phosphate Ca₃(HPO₄)₂ . The calcium phosphate also starts to breakdown and reacts with remaining sodium bicarbonate as the baking temperature rises (Brodie & Godber, 2007).

SAPP (sodium acid pyrophosphate) releases carbon dioxide only with  sodium bicarbonate as the temperature has risen above a certain point (De Leyn, 2014). Glucono-delta-lactone on the other hand is an ester of gluconic acid which spontaneously hydrolyses in water. It reacts with sodium bicarbonate producing a sustained and gradual release of CO2 over the time period of baking. Hydrolysis in water is temperature dependent so the higher the baking temperature the faster the rate of reaction (De Leyn, 2014) .

Coatings

Particular leavening agents, commercial baking powders and leavening acids will use coated particles to minimise premature reactions between carbonates and acids. Coatings and release agents come in many forms. The release agents used include starch from various cereals, various phosphates, fumed silica, silicon dioxide, fats or mixtures of the substances mentioned above. Coatings consist of lipid layers or sparingly soluble calcium phosphate (Kuhnert et al., 2011).

Active Dry Yeast

The addition of dry yeast (Saccharomyces cerevisiae) to bread mixes is one way of introducing an agent that produces carbon dioxide. Yeast produce ‘zymase’ which breaks down sugars to produce readily usable energy as well as ethanol and carbon dioxide. The alcohol produces disappears in vapour during the baking process. The carbon dioxide gas produced causes the dough to rise.  The presence of yeast also gives baked goods especially bread part of its characteristic flavour and aroma. It is the classic and well established biological approach to a rise in dough. Some bakers have tried both soda and dried yeast to obtain a rise. 

Unleavened breads do not use yeast and so are flatter and denser because no carbon dioxide is produced.

Modified forms of yeast have been produced which have indirectly been used to produce both protease and lipase as well as produce carbon dioxide. In some cases these modified yeasts have advanced metabolic machinery which produces more quantities of enzyme for metabolizing sugar as well as enzymes with greater amylase activity and with enhanced sugar transport systems. Whilst the leavening capability of the bread remained unchanged there was a recombinant yeast that produced a lipase that helped stabilise the starch granules and thus improved bread volume (Paciello et al., 2015).

Encapsulated yeast has been investigated for its leavening ability. Freezing affects yeast performance. Hydrogels have been explored as a way of protecting yeast in frozen dough. More specifically, free yeast cells have been replaced with calcium alginate-yeast cells (CAY) or calcium alginate–starch yeast cells (CASY) hydrogels (Cozmuta et al., 2021). It appears to allow for leavening of the dough once it has reached an appropriate temperature following freezing. The implication is significant because it is an example of how to extend the processing options possible.   . 

Bacteria and Sourdough

Bacteria can also be successfully used to leaven bread and this is part of the process of making sourdough. The main bacteria used is Lactobacillus sanfrancisco which is often used in conjunction with Saccharomyces exiguus which is a nonbakers’ yeast. The bacteria metabolises maltose in the bread producing acetic acid, lactic acid and carbon dioxide gas.

In all cases, whether yeast or bacteria is used, a fermentation is only as effective as the substrate being metabolised. It needs to be significantly long enough for reactions to occur. The conditions of fermentation must also be controlled at ambient such as temperature and humidity.   

The Use Of Steam

 One of the simplest yet seemingly unexciting processes for leavening bread is to use steam. For any one interested in this, it is just water vapour which is produced when dough is baked and reaches 212ºF (100ºC) and the liquid water trapped in the dough becomes steam.

The volume of steam is 1,500 times that of liquid water so with that type of expansion when a phase change like that occurs we are going to see some serious dough leavening. The effect is magnified too by baking temperatures. I only know of two baked products that rely on steam: choux and puff. As you can tell by steam leavening, the baked dough is mostly flaky and extremely light.

The use of steam comes into its own when generating flaky pastry as in puff pastry. It relies on incorporating butter into the dough and then rolling it into many folds like the leaves of a book. There are then many tens to hundreds of layers. These form separated flaky layers because of the steam produced in the dough from water in both it and the butter.

The production of choux is different. These are eclairs and beignets. In the baking process, the gluten protein is partly denatured. The elasticity of the dough falls. The starch however is gelatinized which helps structure the choux. It also helps that when steam is formed the pastry just inflates without relaxing to its original physical state and so the shape is held. Any air pockets in the pastry remain intact.

Mechanical Leavening

Mechanical leavening is a process used in baking that incorporates air into doughs and batters, thereby creating a light and airy texture in the finished product. This method relies on physical actions, such as mixing, beating, or whisking, rather than chemical leavening agents (like baking powder or baking soda) or biological leavening agents (like yeast).

Mechanical leavening is achieved by the process of creaming. In this technique, sugar crystals are beaten with solid fat such as butter with a spoon or in a mixer. Air is incorporated into the mixture as tiny bubbles. The sugar crystals effectively cut up the butter. A chemical leavening agent such as baking soda is added to help with further raising.  

Leavening can also be achieved through  other mechanical means, such as beating eggs or creaming butter and sugar together, which incorporate air into the dough or batter. In addition, steam can also be used to leaven baked goods, as the steam causes the dough or batter to expand and rise.

To elaborate further on the key techniques are these:

• Whisking: Rapidly whisking ingredients, such as eggs or egg whites, incorporates air into them, creating a foam. This foam structure helps to leaven baked goods like soufflés, meringues, and sponge cakes.
• Beating: Beating ingredients together, especially butter and sugar, traps air in the mixture. This creaming method is commonly used in making cakes and cookies, where the air trapped during beating contributes to the rise and light texture of the final product.
• Folding: Gently folding whipped egg whites or whipped cream into a batter can add air without deflating the mixture. This technique is often used in delicate recipes like mousse and angel food cake.
• Kneading: In bread making, kneading dough helps to develop the gluten network, which can trap air bubbles created during mixing. While not primarily a mechanical leavening method, it contributes to the structure and texture of the bread.

What examples do we have mechanically leavened products?

• Sponge Cake: Made by whipping eggs (whole or separated) and folding in flour and other ingredients, relying on the trapped air for leavening.
• Angel Food Cake: Uses whipped egg whites as the sole leavening agent, folded into the batter to create a light and airy cake.
• Chiffon Cake: Combines the richness of a butter cake with the lightness of a sponge cake, incorporating whipped egg whites for leavening.
• Soufflés: Made by folding whipped egg whites into a flavoured base, which puff up during baking due to the trapped air expanding

The use of overpressure mixing (OM) to improve the expansion of baked foods has been tried. It produces an increase in the gas volume fraction in the dough which invariably produces a higher final volume. It is not clear if the bubble number and bubble size increases or just one aspect of this following the application of OM. Massey et al., (2001) states that the bubble size increases because of two phenomena. The first is bubble expansion when the overpressure is removed and there is a return to atmospheric pressure. The second part is desorption where solubilised gas as a result of added extra gas pressure then comes out of solution. Sadot et al., (2017) considers the increase in overpressure to cause an increase in the apparent density of the incorporated air which and that additional air is incorporated adding to the total volume of air incorporated. 

A recent approach used the mixing of a cake batter under gas pressure with no baking powder present. The idea was to force the aeration of the batter and thus solubilise any gas into solution. In this system, a mixture of air, carbon dioxide and nitrogen was applied (Palier et al., 2022). A CO₂ pressure of 0.3 and 0.5 bar produced the best results in terms of specific volume of cake with 2.5 mL/g. This was 89% of the specific volume of control cake with baking powder.

Nitrogen gas has been tried and tested. In brewing, smaller but more profuse gas bubbles are generated which form a denser but smoother foam. The same idea is feasible with bubble production in dough. Unfortunately, results to date are not promising because nitrogen gas is poorly soluble in water. It’s also highly unlikely that this gas can be effectively sparged through a dough. One study showed it was effective at increasing the gas fraction in the batter during OM but due to its low solubility didn’t contribute to oven rise during baking through the process of gas dilatation by heating (Brijwani et al., 2008).

The Chorleywood process which is covered by patent GB 1044616 A involves the application of a pressure/vacuum sequence to provide adequate air uptake from the atmosphere followed by rapid application of partial vacuum for bubble structure control. It is certainly not now a novel process.

Ultrasound Technology

The use of ultrasound waves is claimed to enhance the activity of leavening agents by promoting better gas dispersion and increasing the efficiency of gas production. This technology can also help in achieving finer and more uniform crumb structures.

Ultrasound or ultrasonication reduces both internal and external resistance to mass transfer in doughs through the process of cavitation as well as generating microscopic channels via convection.

Proving

A critical process step in generating a light aerated texture is the need for proving before baking. It is much more significant as a step than baking itself because mechanical or physical handling of the dough after proving can cause carbon dioxide to leave the dough.

Flavour Creation

As well as leavening gas producing the rise, various flavour precursors are generated during proofing that contribute to the flavour and aroma profile. These develop further during baking and are part of a series of Maillard reactions. Key components include 3-methyl-1-butanol (alcoholic flavor), 2-phenylethanol (floral), 2,3-butanedione (buttery), phenylacetaldehyde (honey-like aroma), 3-methylbutanal (malty).

Analysis of Leavening Performance

The aeration of dough during proving and mixing is best measured using measurements of dough density immediately following mixing (Chin et al., 2005).

Considerations & Issues 

Biological leavening is not always suitable for particular doughs. If the dough has a very high sugar or fat content then the activity of yeast in particular is suppressed. This implies that the moisture content of the dough is low.  In some cases proving is conducted at much higher temperatures as in oven leavening. 

If the moisture content of the dough is very low, only chemical leavening is possible. The amount of chemical leavener used must be chosen carefully to avoid producing undesirable aromas.

We have already mentioned the undesirable flavours from chemical leavening agents. The pyrophosphates such as acid sodium pyrophosphate leave a distinct unpleasant flavour note. 

Staghorn salt promotes the formation of acrylamide in gingerbread (Komprda et al., 2017). 

Summary

To encapsulate then on all these possibilities, the purpose of raising and leavening in baking is to create a light, airy texture in the finished product. Leavening agents, such as yeast, baking powder, and baking soda, release gases that get trapped in the dough or batter and create small air pockets that expand when the baked good is heated. Leavening is an essential step in bread-making and is used in a variety of other baked goods to achieve the desired texture and flavour.

References

Brijwani, K,. Campbell, G.M., Cicerelli, L. (2008) Chapt. 37 – Aeration of Biscuit Doughs During Mixing. In:  In “Bubbles in Food 2: Novelty, Health and Luxury.” eds. Campbell, G.M., Scanlon, M.G. and Pyle, D.L., Am. Assoc. Cereal Chem, pp. 389-402.

Brodie, J., Godber, J., (2007). Bakery Processes, Chemical Leavening Agents. Kirk-Othmer Encyclopedia of Chemical Technology. (Article).

Carullo, G., Scarpelli, F., Belsito, E. L., Caputo, P., Oliviero Rossi, C., Mincione, A., … & Aiello, F. (2020). Formulation of new baking (+)-catechin based leavening agents: Effects on rheology, sensory and antioxidant features during muffin preparation. Foods, 9(11), 1569

Chin, N. L., & Campbell, G. M. (2005). Dough aeration and rheology: Part 1. Effects of mixing speed and headspace pressure on mechanical development of bread dough. Journal of the Science of Food and Agriculture, 85(13), pp. 2184-2193.

Cozmuta, A. M., Jastrzębska, A., Apjok, R., Petrus, M., Cozmuta, L. M., Peter, A., & Nicula, C. (2021). Immobilization of baker’s yeast in the alginate-based hydrogels to impart sensorial characteristics to frozen dough bread. Food Bioscience, 42, 101143.

Cozmuta, L. M., Nicula, C., Peter, A., Apjok, R., Jastrzębska, A., & Cozmuta, A. M. (2022). Insights into the fermentation process of fresh and frozen dough bread made with alginate-immobilized S. cerevisiae yeast cells. Journal of Cereal Science, 107, 103516. .

De Leyn, I., (2014). Other Leavening Agents. In:  Bakery Products Science and Technology: second Edition 9781119967156, pp. 175–181 (Article). 

Frühling, Y., Claßen, T., Mobarak, M., Bauer, M., Zettel, V., Gatternig, B., … & Delgado, A. (2023). CO2 gas hydrate as an innovative leavening agent for baked goods. Future Foods, 7, 100213.

Kollemparembil, A. M., Srivastava, S., Zettel, V., Gatternig, B., Delgado, A., Jekle, M., & Hitzmann, B. (2023). Application of CO2 Gas Hydrates as Leavening Agents in Black-and-White Cookies. Foods, 12(14), 2797

Komprda, T., Pridal, A., Mikulíková, R., Svoboda, Z., Cwiková, O., Nedomová, Š., & Sýkora, V. (2017). A combination of additives can synergically decrease acrylamide content in gingerbread without compromising sensory quality. Journal of the Science of Food and Agriculture, 97(3), pp. 889-895.

Kuhnert, P., B Muermann, B. U-J. Salzer (2011) Handbuch Lebensmittelzusatzstoffe. Behr’s Verlag, Hamburg (2011)

Martin, P. J., Tassell, A., Wiktorowicz, R., & Morrant, C. J. (2008). Chapter 20: Mixing Bread Doughs Under Highly Soluble Gas Atmospheres and the Effect on Bread Crumb Texture: Experimental Results and Theoretical Interpretation. In “Bubbles in Food 2: Novelty, Health and Luxury.” eds. Campbell, GM, Scanlon, MG and Pyle, DL, Am. Assoc. Cereal Chem, pp. 197-206.

Murat Karaoğlu, M., Gürbüz Kotancilar, H. (2006) Effect of partial baking, storage and rebaking process on the quality of white pan bread. Int. J. Food Sci. Technol. 41, pp. 108–114

Paciello, L., Landi, C., Orilio, P., Di Matteo, M., Zueco, J., & Parascandola, P. (2015). Bread making with Saccharomyces cerevisiae CEN. PK113‐5D expressing lipase A from Bacillus subtilis: leavening characterisation and aroma enhancement. International Journal of Food Science & Technology, 50(9), pp. 2120-2128.

Palier, J., Le-Bail, A., Loisel, C., & Le-Bail, P. (2022). Substitution of baking powders in a pound cake by an overpressure mixing process; impact on cake properties. Journal of Food Engineering, 316, 110824.

Srivastava, S., Kollemparembil, A. M., Zettel, V., Claßen, T., Mobarak, M., Gatternig, B., … & Hitzmann, B. (2022). An innovative approach in the baking of bread with CO2 gas hydrates as leavening agents. Foods, 11(22), 3570.

Vernon-Carter, E. J., Garcia-Diaz, S., Reyes, I., Carrillo-Navas, H., & Alvarez-Ramirez, J. (2017). Rheological and thermal properties of dough and textural and microstructural characteristics of bread with pulque as leavening agent. International Journal of Gastronomy and Food Science, 9, pp. 39-48.  

Vetter, J.L. (2003). Leavening agents. In Caballero, B. (ed.). Encyclopedia of Food Sciences and Nutrition. 2nd ed. Elsevier Science. pp 3485-3490.