As bakeries morphed from craft shops to massive dedicated facilities, the time constraints of commercial production necessitated the use of prepared commercial yeast.
Although employing natural sourdough starters slows down a process, some bakers believe it is necessary to garner the taste, color and aroma of artisan breads.
Chemical leaveners depend on the reaction of a base ingredient, such as sodium bicarbonate, with an acid ingredient, such as sodium, aluminum and calcium phosphates. Chemical leaveners depend on the reaction of a base ingredient, such as sodium bicarbonate, with an acid ingredient, such as sodium, aluminum and calcium phosphates. This reaction occurs when the dough is subjected to either heat or moisture. Double-acting baking powders react to both.
During the origins of civilization, man discovered that by grinding wheat grain he could create a paste with nutritive value. Soon after, it was discovered that by flattening and baking this paste, a product could be conveniently held and transported. The next real baking breakthrough occurred later when some lazy lout decided—after milling his grain and mixing up his dough—to take a day or two off.
Naturally occurring airborne yeast spores found a home in and on this primitive dough as it was being mixed. In conjunction with the moisture and air in and around the dough, and the residual sugars from the grain, these unseen microscopic plants began to metabolize, giving off carbon dioxide (CO2) gas and converting simple sugars into alcohol.
When the prehistoric baker finally returned to his task, he discovered that his unattended dough had miraculously grown in size. The protein in the flour had provided the strength to form millions of tiny cells while the CO2 gas trapped inside caused each of them to swell like millions of little balloons. Throwing caution to the wind, the baker baked the dough, which led to an even more pleasant surprise: The airy cells inside the dough expanded even further during baking, giving the resulting product a light, pleasant texture.
However, something else had occurred. The trace amounts of alcohol produced by this natural fermentation had given the bread a wonderful aroma and taste, and had helped dissolve the bonds holding the dough together, eliminating the doughy texture of unleavened breads.
Hence, an industry was born and leavening was the key to its success.
Generally, leavening systems fall into three categories: steam/air, chemical and biological (such as yeast). Steam/air leavenings are associated with items such as puff pastry and most cakes. In puff pastry, roll-in shortening contains a relatively high percentage of moisture. As the product is baked, this moisture expands as it is converted to steam. Trapped within the laminations of the dough, it causes them to separate and rise. In cakes, air is whipped into the batter during mixing and retained by protein from the flour and egg whites, which loosely bonds the batter together. Expansion of this trapped air during baking gives rise to cakes.
Chemical leavening systems are found in a wide variety of bakery foods such as biscuits, cake donuts, sweet muffins and cookies. CO2 produced by a chemical reaction, usually between sodium bicarbonate and an acid, provides rapid leavening during these products' short bake times.
Biological leaveners encompass naturally occurring airborne yeasts, starter cultures from previously produced doughs and commercially prepared yeasts that are available in bulk-compressed, dry instant and liquid forms.
Biological leavening agents
Airborne yeasts are thought to be responsible for the first fermentations, providing alcohol to beer and wine and giving rise and flavor to yeastraised breads. Shortly after, it became common practice to save a percentage of each batch of dough to seed the following batch. Further innovation led to the use of sediment left over from the brewing of beer to help start the fermentation process.
As bakeries morphed from craft shops to massive facilities, the time constraints of commercial production necessitated the use of prepared commercial yeast.
However, consumer trends toward artisan breads are forcing renewed interest in extended fermentation and natural starters. For example, par-baked artisan bread manufacturer Ecce Panis built a new plant last year that automated artisan bread production. As part of its processing line, the company installed an automated sour system to house its 14-year old starters.
Although employing natural sourdough starters slows down a process, some bakers believe it is necessary to garner the taste, color and aroma of artisan breads. Sourdough starters are created by mixing flour and water, then waiting for the "magic" to happen. Over time, this mixture will ferment from yeast particles in the air. After the starter has been developed, bakers will incorporate a percentage of the starter in each batch, and feed the starter with equal parts of water and flour to continue its growth.
Control is key
Although creating a natural sour and leavening system can produce quality artisan breads with authentic tastes, many bakeries simply do not have the flexibility to invest in an automated sour system. However, these bakers can still produce artisan-like products using commercial yeast and reduced fermentation times.
Yeast, like any plant, has special requirements for optimal growth. With the natural fluctuations in yeast and flour components, the key is to specify both as tightly as possible, then rigidly control the environment in which they have to interact.
"Fermentation control and consistency is key," says one yeast supplier. "Fermentation time, temperature, the pH of the dough and factors such as the percentages of sugar, water, salt, and mold-inhibitor all contribute to the success of the product."
The optimum temperature for yeast growth is 75°F to 85°F. It also is critical to monitor relative humidity. It is estimated that for every degree in increased temperature, the rate of organism growth is 3% to 5%. Water availability in dough also helps determine the rate of rise. Stiffer doughs rise slower than slacker ones.
The hardness of the water also is important. Medium soft water (50 to 100 ppm) is optimum for bread production,according to the American Institute of Baking. Soft water (0 to 50 ppm) will produce a slack dough and bread with an open grain. Hard water (200 ppm and higher) can affect the pH of the dough, retarding yeast and enzyme activity.
The choice of ingredients also helps determine the rate and amount of rise yeast will provide bakery foods. Bread dough generally consists of flour, water, sugar and salt, but the ratio of these ingredients is critical. Sugar represents food to yeast, and is essential to its growth. Conversely, salt acts as a buffering agent, preventing the yeast from running wild. Too little or too much sugar or salt can destroy the product.
"One of the most effective ways of continuously monitoring the process time and dough temperature is with the use of process control charts, which provide a visual guide for operators," one yeast supplier says.
Yeast fermentation improves doughhandling characteristics by loosening the dough, enhancing gas retention, improving the finished product's texture, providing desirable flavor, and extending the shelf life of the final product. Yeast activity starts with the addition of moisture to the flour/sugar/yeast mixture and does not end until baking, when the yeast is killed by heat. Therefore, control of the proofing process is critical to the finished product.
Long fermentation or proofing times permit full hydration of the starch and formation of long strands of gluten, which aids in machineability and handling. The long fermentation process also helps retain the gas in dough, provides an ideal crumb and aids in extending shelf life because of the action of the amylase on broken starch.
When producing artisan breads, bakers also can implement a preferment that aids in gluten production and determines the texture and taste of the final product. Consisting of combinations of dough ingredients (flour, water, sugar and yeast) in varying ratios, yeast preferments are allowed to work anywhere from 20 minutes to several hours before addition to the rest of the bread ingredients. This added step means increased production time, but produces loaves in the European tradition.
Chemical leavening agents
Chemical leavening systems are used in products such as cookies or cake donuts, where the leavening's reaction times need to be quick, and the flavor profiles do not require fermentation. In addition, they can be used in frozen and par-baked versions of traditionally yeast-raised, bake-off products to augment the action of the yeast killed during freezing and thawing.
When this happens, the ensuing reaction is the formation of CO2, which gives rise to bakery foods. The release profile of the reaction is reported as the Dough Rate of Reaction (DRR). The DRR measures the CO2 level produced during a certain time and under certain conditions, including whether the action occurs at hydration, as a time-released reaction, or if it is heat-activated.
Products such as self-rising frozen pizza doughs and freezer-to-oven (or microwave) cinnamon rolls use a combination of yeast and chemical leaveners to achieve both flavor and performance. In these products, heat-activated chemical leavening systems ensure that products do not rise prematurely.
Encapsulated leavening systems also allow bakers to control when a product rises by preventing the leavening from coming into contact with moisture. This is accomplished by encapsulating the granules of leavening with a coating, which will not melt off until a given temperature is reached.
In self-rising pizza crusts, bakers can supplement or replace yeast with encapsulated chemical leaveners to ensure that the leavening reaction will not occur during the freeze-thaw cycle. In "wet" items such as frozen muffin batters, coated leavenings can keep the leavening action in check until the thawed batter is in the oven. "Use of encapsulated ingredients naturally add some cost to the product," says a supplier of these systems. "But, it adds value for the functionality benefit. Products last longer and perform better."
Keeping up with current baking trends not only affects the marketing department, but also influences how products are manufactured. With the growing popularity of artisan breads, bakers must review their leavening process to determine if it maintains the quality that artisan bread demands. On the opposite side, the popularity of frozen and par-baked dough applications require bakers to look at chemical leavening to ensure products rise when they are supposed to.