YeastYeast, a living organism, is activated by moisture, heat and food. Through fermentation, yeast converts dough carbohydrates into carbon dioxide and ethanol. The resulting gases provide the rise in volume of the dough and give lightness to a loaf of bread. Yeast also affects dough rheology through oxidization and causes the dough to become elastic. Additionally, yeast adds a unique flavor and bread-like texture to baked goods.
Yeast appears in various types and forms including liquid, compressed and crumbled. Different types of yeast can be used interchangeably by adjusting the liquids in a recipe. Instant yeast was developed to rise more rapidly and can be added directly to the flour without initial rehydration. When instant yeast is used, the first rise or proof can be replaced with a 10-minute rest, greatly reducing proof time.
Formed yeast items are put into a heat- and humidity-controlled fermentation cabinet for proofing. Fermentation time varies, but it can take up to an hour or more to raise a product to nearly its full height. More volume is gained in the first few minutes of baking before the yeast cells die from the elevated heat.
Although yeast can be a flexible ingredient, it does have its own limitations that must be considered. “Yeast is negatively impacted by both chocolate and cinnamon. For this reason, when these ingredients are used in yeast products, they are typically rolled into the dough, such as with cinnamon rolls, or drizzled on the dough, instead of being mixed into the dough with the yeast. Salt also affects yeast growth. Too much salt inhibits yeast growth, but too little salt negatively affects flavor and causes too much yeast growth, which results in a collapsed loaf due to over-rising,” explains Diana McElroy, a registered dietitian at a well-known yeast supplier.
As baking science has advanced, chemical leavening agents have been created, and according to John Brodie, bakery technical service manager for a leavening supplier, “The mechanism for yeast is vastly different than for chemical leavening.” Consequently, the chemical leaveners have their own individual attributes.
PhosphatesLeavening phosphates are an acid in which a basic bicarbonate source needs to be added, the most widely used source being sodium bicarbonate (baking soda). The leavening acid liberates the carbon dioxide from the bicarbonate at various speeds, depending on the type of leavening acid used.
Phosphate leavening agents are selected based upon NV (neutralizing value), rate of reaction, processing conditions, product format, convenience and health aspects. NV is a measure of how “strong” the acid is and helps to determine how much acid is required in the formulation. NV is generally expressed as the parts of sodium bicarbonate that are neutralized by 100 parts of leavening acid. The range of NV in available leavening acids is from 33 to over 100.
There are three main types of leavening phosphates: calcium phosphate (monocalcium MCP and dicalcium phosphate DCP), sodium aluminum phosphate (SALP) and sodium acid pyrophosphate (SAPP). From these three, suppliers have developed products with unique characteristics for specific applications.
“One popular leavening agent preferred by the baking industry is sodium aluminum phosphate, because it is heat-triggered, provides excellent volume and consistent finished product characteristics,” contributes Barbara Heidolph, market development manager at a supplier of phosphate leaveners to the baking industry.
Calcium acid pyrophosphate (CAPP) was developed to aid bakers in formulating healthier products that contain a good source of calcium without additional sodium. CAPP can be used in dry mix, frozen and refrigerated systems in place of traditional leavening acids to achieve specific nutritional targets for sodium reduction or calcium fortification. “When CAPP is used to replace SAPP, bakers can achieve significant, sometimes greater than 25%, reduction in sodium, still maintaining desired volume. CAPP provides a clean flavor profile preferred by many to SAPP. There is no sodium taste, astringency or off-flavor,” adds Heidolph.
“SAPP can contribute a ‘pyro’ aftertaste, where SALP and calcium phosphates are neutral in taste. SALP gives a soft, resilient texture, where MCP (monocalcium phosphate) will give a slightly firmer texture. SAPP gives a soft texture but is not as resilient or ‘springy.’” SALP is mainly heat reactive, where the MCP releases more carbon dioxide at room temperature. SAPP reacts from fast to slow, depending on the type (there are five or more types of SAPP), explains Brodie.
Reaction RateThere are basically three types of reaction rate: fast, time-delayed and heat-triggered. Fast leavening agents provide nucleation during mixing and help establish the grain of the final product. In high-temperature baking, these agents can be very important in providing rapid early expansion.
Time-delayed leavening acids provide bench or floor time. They are designed to react after a certain period of time. This is particularly important in operations where there are large batches or where a dough or batter will be processed over an extended period of time.
Heat-triggered leavening agents undergo the majority of their reaction after an activation temperature has been reached. In general, activation temperatures are greater than 100°F. “This delay based on temperature activation provides the ultimate in bench tolerance or floor time,” states Heidolph.
Pizza“Self-rising pizza is one item that often uses a combination of yeast and chemical leavening. It requires very little to no proof time and relies on the chemical leavening to raise it in the oven. The yeast provides some initial carbon dioxide and gives the pizza its traditional ‘yeasty’ flavor. More and more bakery producers are finding the value of using chemical leavening in traditional yeast products. For frozen ready-to-bake rolls, some yeast is used to achieve fermentation volume; the product is then frozen. The end user puts the rolls directly from freezer to oven, where the chemical leavening provides the final volume in the oven,” adds Brodie.
CakeChemically leavened products like cake often require a combination of acids. This is driven by the profile necessary for carbon dioxide release. In cake, typically a fast leavening agent such as MCP will be used with SALP. The fast leavening agent provides the initial reaction and helps to set the desired cell structure. SALP then provides maximum expansion and volume of the finished cake.
Frozen ProductsIn frozen products such as unbaked frozen biscuits, a combined system of leavening acids performs best. “A slow SAPP along with SALP provides the ideal combination of bench tolerance—delayed reaction allowing the processor to get the dough frozen, combined with ultimate storage stability and maximum bake performance,” adds Heidolph.
Dry MixFor dry mixes the key consideration is to ensure leavening stability during storage to prevent pre-reaction of the bicarbonate. Although a leavening acid like MCP may be involved, other factors such as flour moisture, storage temperature and particle size of the bicarbonate also contribute to storage stability.
Refrigerated Doughs and BattersGenerally, refrigerated doughs are stored in packaging that helps retain the carbon dioxide under pressure. The classic example is canned refrigerated dough. In these applications, slow leavening agents like SAPP and SALP are used; they allow the dough to be processed and placed in the can. Once the can is sealed, the leavening reaction occurs. When the product is baked, the carbon dioxide expands and provides volume.
Refrigerated batter products generally are formulated with heat-triggered leavening systems in order to minimize any reaction during storage. SALP or SALP in combination with MCP is preferred.
EncapsulationLeavening acids and bicarbonate are available in encapsulated formats. The protective coating allows leavening gas to be released only at a specific time or after specific conditions have been met. A coating of fat will delay gas release until the coating is melted (temperature delay). When water-soluble coatings are used, the gases are released only after a specific amount of time.
Encapsulation may help in applications where a standard leavening acid will not provide the desired outcome on its own. Examples are products requiring refrigeration for long periods of time, where even heat-triggered leavening agents can eventually undergo hydrolysis and low levels of pre-reaction. Encapsulation does add additional cost to the formulation, however, and is generally not preferred.
Reaction ConsiderationsThere are times when ingredients in a bakery formula react with sodium bicarbonate, either in a dry state or in a batter or dough, causing the carbon dioxide to release prematurely. Acidic ingredients like fruit or juices, buttermilk and organic acids added for other purposes can cause such reactions. Ultimately, these acid components reduce the overall quantity of carbon dioxide available to lift and expand the product, leading to poor volume or coarse crumb structure.
“Another consideration is the effect of the leavening system on the final pH of the baked product. The pH can impact color of the grain and crust. The lower the pH, the whiter the crumb appears. With regards to crust, it has less browning with lower pH. At higher pH, crumb is more yellow or creamy in appearance and crust has potential to be darker brown,” adds Heidolph. Brodie offers that, “chocolate cakes often use excess sodium bicarbonate, increasing pH, thus having a darker color. The amount of leavening used also affects the finished volume. Trials are typically done to optimize the amount and types of leavening used.”
The pH can also impact the color of inclusions such as blueberries or the crumb around them can take on a “greenish cast instead of blue,” advises Heidolph.
There are times where encapsulation can be used to help prevent negative interactions, especially in yeast systems, as yeast activity can be inhibited by a number of factors including pH, sodium chloride, ions and preservatives. Thanks to discoveries in chemical leavening, manufacturers can produce consumer-friendly options using cost effective processes.