Chemical Leaveners in Baking
Chemical Leaveners in Baking Leavening action can occur in several different ways — through biological reactions, physical or mechanical actions, thermal decomposition, or chemical neutralization. Biological reactions occur most often through yeast fermentation, which produces carbon dioxide in a dough system. Physical or mechanical action, on the other hand, refers to incorporation of air or steam through the physical motion of mixing. Whipping batters can trap air into egg whites, whole eggs, or creaming of shortening and sugar. Both mixing and whipping allow the air that is introduced into the batter system to be trapped and provide leavening action. Steam is a supplementary form of leavening and provides significant leavening in all products. Chemical neutralization and thermal decomposition are components of the chemical leavening process. The acid/base reaction most commonly used to create the baking powder system relies on several properties to produce a desirable final product.
ACID/BASE SYSTEMS One of the most widely recognized chemical leavening systems is the acid/base system, which is the chemical reaction of an alkaline (base) material and an acid salt using heat and moisture. This equation produces a neutral salt, carbon dioxide, and water, with the release of the carbon dioxide gas producing the leavening action in a batter system. Figure 2 shows this reaction using sodium bicarbonate, which is popular for use in commercial baking powders. Composed of the bicarbonate source and the acid salt, the leavening system — due to the release of carbon dioxide — can affect the volume, shape, and texture of the finished product, so bakers should choose the leavener wisely. It can react with other ingredients to contribute to the internal structure of the finished product, influencing grain, cell wall size, finished product pH, crumb color, flavor, and resiliency. Nucleation and the cationic and anionic effects can also influence these characteristics.
Nucleation Nucleation occurs during the mixing stage. Once the leavening system has been fully hydrated and is a complete batter system, the act of mixing creates gas bubbles. Most batters require formation of nucleation sites during mixing. The cells produced during mixing are where the bulk of the leavening diffuses into bubbles and expands. Batters cannot create their own cells; they require the mixing action, the initial leavening release, and an adequate emulsification system to produce them. Increasing the number of nucleation sites receiving leavening gas can reduce the average size of the individual bubbles, leading to a finer texture in the finished product. A better dispersion of bubbles will result in a finer grain and thinner cell walls. If the bubbles rise too quickly and escape from the batter system, it can lower the volume, as well as create a tight grain on the bottom and an open grain on the top of the product. Because bubble nuclei form only during mixing, the final product grain is determined by the amount of nucleation during mixing. The initial gases may originate from several sources. The mixing operation incorporates air into the batter. Reaction of ingredients with the bicarbonate source can prematurely react and produce carbon dioxide. However, the leavening system can be designed to produce carbon dioxide at this stage, if desired. Double-acting leavening systems are used to provide supplemental nucleation and finish with additional reaction in the oven. The final reaction occurs in the elevated temperatures of the oven. The reaction supplies the gas to expand the small bubbles until the starch gelatinizes, setting the product’s crust. If large bubbles are present, the cell walls will produce a large, opentextured product. If the cell walls are too large, the product may be at risk of collapsing, or may contain holes and tunneling.
Ionic Effects Chemical leaveners can influence the texture of a product through the cationic and anionic effects. Ionic bonds are bonds between ions of opposite charges. The overall effect of ions is to increase association and interaction between ingredient components, resulting in increased rigidity and altering finished texture. Phosphate leaveners contain sodium, calcium, and/ or aluminum ions. Sodium ions give a soft texture but do not produce products that are as resilient, while high levels of sulfate ions tend to weaken the batter’s protein structure. Pyrophosphate ions can react with proteins to increase moisture absorption and retention capacities. Cations like calcium and aluminum improve the crumb by strengthening the protein phase of the batter and promoting thin cell walls. Calcium ions contribute to the structure and help the protein matrix in flour, giving a slightly firmer texture, but also produce a finer grain and thin cell walls. Aluminum leaveners react similarly to calcium ions in the finished grain and cell walls. Using aluminum salts yields a soft and resilient texture. The strength contributed to batter comes from either calcium or aluminum ions reducing the tendency of the small bubbles to coalesce into larger cells.
Effects of pH The term pH refers to the amount of acidity or alkalinity of a product, based on the concentration of hydrogen ions. In baked products, pH influences the finished product color and texture. A higher pH (more alkaline) will create a darker color with a finer texture. A lower pH (more acidic) will create a lighter color with a less fine texture. In addition, products with a lower pH have a slightly longer shelf-life. Ideally, bakers choose to balance the acids and bicarbonates in the leavening system. However, altering the amounts of bicarbonate or acid salts can change the pH of the final product.
BASES Historically, sodium bicarbonate has been the traditional basic (alkaline) portion of chemical leavening. There are two other acknowledged bicarbonate sources. Each basic portion has different characteristics that bakers can utilize depending on the desired characteristics of the bakery product. See Figure 1 for a simple comparison of the products. Figure 1. Sodium Bicarbonate v. Potassium Bicarbonate v. Ammonium Bicarbonate.
Chemical Formula
pH
% Solubility at 68°F
% Solubility at 104°F
(mg/100g portion)
Sodium Bicarbonate
NaHCO3
8.3
9
11
27,360
Potassium Bicarbonate
KHCO3
8.4
33
45
276
Ammonium Bicarbonate
NH4HCO3
7.9
17
23
ACID/BASE SYSTEMS One of the most widely recognized chemical leavening systems is the acid/base system, which is the chemical reaction of an alkaline (base) material and an acid salt using heat and moisture. This equation produces a neutral salt, carbon dioxide, and water, with the release of the carbon dioxide gas producing the leavening action in a batter system. Figure 2 shows this reaction using sodium bicarbonate, which is popular for use in commercial baking powders. Composed of the bicarbonate source and the acid salt, the leavening system — due to the release of carbon dioxide — can affect the volume, shape, and texture of the finished product, so bakers should choose the leavener wisely. It can react with other ingredients to contribute to the internal structure of the finished product, influencing grain, cell wall size, finished product pH, crumb color, flavor, and resiliency. Nucleation and the cationic and anionic effects can also influence these characteristics.
Nucleation Nucleation occurs during the mixing stage. Once the leavening system has been fully hydrated and is a complete batter system, the act of mixing creates gas bubbles. Most batters require formation of nucleation sites during mixing. The cells produced during mixing are where the bulk of the leavening diffuses into bubbles and expands. Batters cannot create their own cells; they require the mixing action, the initial leavening release, and an adequate emulsification system to produce them. Increasing the number of nucleation sites receiving leavening gas can reduce the average size of the individual bubbles, leading to a finer texture in the finished product. A better dispersion of bubbles will result in a finer grain and thinner cell walls. If the bubbles rise too quickly and escape from the batter system, it can lower the volume, as well as create a tight grain on the bottom and an open grain on the top of the product. Because bubble nuclei form only during mixing, the final product grain is determined by the amount of nucleation during mixing. The initial gases may originate from several sources. The mixing operation incorporates air into the batter. Reaction of ingredients with the bicarbonate source can prematurely react and produce carbon dioxide. However, the leavening system can be designed to produce carbon dioxide at this stage, if desired. Double-acting leavening systems are used to provide supplemental nucleation and finish with additional reaction in the oven. The final reaction occurs in the elevated temperatures of the oven. The reaction supplies the gas to expand the small bubbles until the starch gelatinizes, setting the product’s crust. If large bubbles are present, the cell walls will produce a large, opentextured product. If the cell walls are too large, the product may be at risk of collapsing, or may contain holes and tunneling.
Ionic Effects Chemical leaveners can influence the texture of a product through the cationic and anionic effects. Ionic bonds are bonds between ions of opposite charges. The overall effect of ions is to increase association and interaction between ingredient components, resulting in increased rigidity and altering finished texture. Phosphate leaveners contain sodium, calcium, and/ or aluminum ions. Sodium ions give a soft texture but do not produce products that are as resilient, while high levels of sulfate ions tend to weaken the batter’s protein structure. Pyrophosphate ions can react with proteins to increase moisture absorption and retention capacities. Cations like calcium and aluminum improve the crumb by strengthening the protein phase of the batter and promoting thin cell walls. Calcium ions contribute to the structure and help the protein matrix in flour, giving a slightly firmer texture, but also produce a finer grain and thin cell walls. Aluminum leaveners react similarly to calcium ions in the finished grain and cell walls. Using aluminum salts yields a soft and resilient texture. The strength contributed to batter comes from either calcium or aluminum ions reducing the tendency of the small bubbles to coalesce into larger cells.
Effects of pH The term pH refers to the amount of acidity or alkalinity of a product, based on the concentration of hydrogen ions. In baked products, pH influences the finished product color and texture. A higher pH (more alkaline) will create a darker color with a finer texture. A lower pH (more acidic) will create a lighter color with a less fine texture. In addition, products with a lower pH have a slightly longer shelf-life. Ideally, bakers choose to balance the acids and bicarbonates in the leavening system. However, altering the amounts of bicarbonate or acid salts can change the pH of the final product.
BASES Historically, sodium bicarbonate has been the traditional basic (alkaline) portion of chemical leavening. There are two other acknowledged bicarbonate sources. Each basic portion has different characteristics that bakers can utilize depending on the desired characteristics of the bakery product. See Figure 1 for a simple comparison of the products. Figure 1. Sodium Bicarbonate v. Potassium Bicarbonate v. Ammonium Bicarbonate.
Chemical Formula
pH
% Solubility at 68°F
% Solubility at 104°F
(mg/100g portion)
Sodium Bicarbonate
NaHCO3
8.3
9
11
27,360
Potassium Bicarbonate
KHCO3
8.4
33
45
276
Ammonium Bicarbonate
NH4HCO3
7.9
17
23
