Designing Bakery
Products
January 1994 -- Cover Story
By: Scott Hegenbart
Editor*
*(April 1991-July 1996)
In one form or another, bakery foods are common in almost every culture. So much so, in fact, that they form the many diets. This is particularly well illustrated by the new Food Pyramid, since grains and cereals occupy the first tier. Because of this universality, many product designers mistakenly believe that baked products are easy to create - after all, Grandma used to make all this stuff herself, didn't she? In truth, bakery products present greater challenges than many other food products because they require a delicate balance between structure, leavening and processing. Without the right balance, the product will fail.
"There is a combination of science and art in the development of these products'" says Walt Schierioth, manager of technical assistance for the American Institute of Baking, Manhattan, KS. "Food scientists who are just out of college and working in bakery food development, have only the things that were taught to them on which to rely. They do not have the ability to understand the feel for the products. On the other side of the coin, you have a lot of people making these products who have a feel for it, but don't have a lot of education. Still, they know what happens when they put things together."
Creating a bakery food using either a scientific or an artistic approach offers advantages and disadvantages. The best approach, perhaps, is to combine artistic flair with a scientific foundation.
"Today, we have the technology to create the products like the artisans, but it isn't typically done because people can make bread without knowing all of the technical background," says David King, group development manager of bakery for Van den Bergh Foods, Rochester, NY. "In fact, many bakeries are reluctant to apply it because it is viewed as overcomplicated. They have the 20-year veteran who knows by feel what's wrong. But you: really want to develop a product where you don't need that seasoned veteran; where you don't introduce that subjectivity."
To take a more objective approach, start by thinking of bakery products as a stool with three legs: framework, leavening and process. Only with each leg doing its part can the product succeed.
Forming the framework
Because bakery foods come in such a wide variety of shapes and sizes, assembling a general set of guidelines is a formidable task. Still, baked products do share a certain universal characteristic - they are combinations of ingredients put together in such a fashion so as to retain gasses that are given off by a leavening system during a baking cycle.
"It's the entrapment of that gas that gives a certain amount of lift to make the product palatable," says Schierioth. "But that's not always true because some things are not leavened in the same respect as a layer cake or a white pan bread."
Trapping gas is the function of a baked product's framework - the dominant component of which is usually wheat flour.
"When you talk about baked products, they are, with a few exceptions, wheat-based," says Schierioth. "Understanding what flour and its components do is important as the basis for all baked products."
"Flour is the starting point for every baked product," says King. "Once you know the texture, appearance and volume you want, select the flour on that basis. In a cake, you want it to be tender; you don't want the flour to contribute to that texture at all. Whereas for bread, you want more resilience, some strength, so you choose a flour with a protein level that can give it to you."
The most substantial portion of wheat flour is composed of protein and starch. These work together to form a viscoelastic dough that can expand and contain leavening gases. Such a dough is not obtained simply by combining flour and moisture, however. Mixing also is required for proper dough development.
Compared with a starch or a protein molecule, a flour particle is large and dense. Water requires a great deal of time to penetrate this particle and solubilize all of the starch and protein. Mixing accelerates this process because flour particles physically rub against each other and the mixer parts. This rubbing removes the softened hydrated flour particle surface, allowing the moisture to penetrate more rapidly to the dry particles beneath.
As the dough reaches full development, the discreet flour particles vanish into fully hydrated starch and protein molecules. The dough's structure essentially is a mixture of protein fibrils dotted with starch granules.
"The protein serves as the studs that are holding up the framework, while the starch serves as the building blocks in-between," says Schierioth. "This is particularly true for batter-type products."
Fixed in the mix
In addition to developing the gluten protein, mixing serves another vital function by incorporating air into the dough. Incorporating air - most importantly, nitrogen gas - is necessary because it forms the cellular structure that is expanded by leavening gasses. (In the case of certain products, like angel food cake, the mixed-in air is the sole leavening.) Contrary to popular belief, leavening gasses don't create the cellular structure, they only fill and expand the bubbles created by mixed-in air.
Another common misconception about leavening gasses is that gluten retains them by forming a membrane barrier. If this were true, it would be impossible for the leavening gasses to get in to the cells. The explanation can be found in the laws of diffusion. Leaveners in the aqueous phase surrounding the air bubbles form carbon dioxide. This gas, subsequently, saturates the aqueous phase. As more and more carbon dioxide is produced, it has no where else to go so it diffuses into the air cells. It is held there because the now saturated aqueous phase prevents it from diffusing out.
While the importance of gluten protein to bakery foods cannot be denied, the effects of other flour components shouldn't be overlooked. Gums are present in wheat flour in the form of both water-soluble and water insoluble pentosans. Research has shown both to be active in the improvement of bread loaf volume.
Rye flour, while containing far less gluten than wheat flour, possesses a much higher percentage of pentosans. According to researchers, rye flour's ability to retain leavening gasses ranks second only to that of wheat flour. The most important factor in this ability is believed to be the pentosan content of rye flour.
In non-yeast-raised products, little gluten development is needed or desired. Consequently, the gas retaining properties in the dough rely more heavily on the starch and pentosan content of the flour and/or other ingredients in the formula.
Flour also contains between 1 and 2% lipids. Swedish researchers have demonstrated that these lipids can form a hexagonal liquid-crystal phase under certain conditions. By adding 2% of these lipids as a liposomal dispersion, a 50:50 blend of wheat and rice flours can produce a loaf of bread possessing a volume comparable to that of a wheat flour control.
Selecting and specifying
Because it provides the fundamental functionality in a baked product, flour has the ability to either make or break a product. Unfortunately, flour as a first-generation agricultural product can be highly variable.
"Bakery products are very sensitive," says King. "They're sensitive to flour changes that can happen year-to-year or day-to-day."
Consequently, product designers will have to know what characteristics of flour will affect their product and specify a flour accordingly. They also must be prepared to make formula adjustments to compensate for differences in flour caused by a new shipment, a new crop year or a change in supplier. These specifications will include both the flour characteristics and the way in which it has been processed:
Wheat type. Flour is milled from both hard and soft wheats. Hard wheat flours have higher levels of starch damage because the milling process must be more rigorous on the harder wheat berries. Hard wheat flour, however, has the protein strength necessary for high-volume, yeast-raised breads and rolls.
Protein quantity and quality. Gluten is responsible for most of the gas retention in yeast-raised products. In these applications, the quantity and quality of the protein in a flour will be the specifications most critical to flour performance. The quality of the protein, in particular, is important because different flours often will perform differently, even if they have the same protein level.
Determining the protein content of a flour is simple when using any one of several tests, such as the Kjeldahl method for determining nitrogen. Determining the quality of that protein, however, is not so simple and will require a bake-test.
Ash content. Ash is composed of residual bran pieces in the finished flour and is indicated by the flour's color. The darker the color, the higher the ash content. According to Marvin Willyard of the Ph. Orth Co. in Oak Creek, WI, ash content is the basis by which flours are graded.
"Ash is typically higher (0.41 to 0.55%) in hard flours and lower in soft flours, varying from 0.35% for cake flour to 0.45% for pastry flours," says Willyard. "The highest quality flour refers to a grade with the lowest ash content and the best baking properties."
Patent flour is the class of flour with the least amount of ash. The low ash content results from the fact that patent flour is obtained toward the start of the milling process.
Clear flour is the next grade below patent flour because of its higher ash content.
"Clear flour is creamier in color than higher grades of flour," says Willyard. "Often, with specks of bran still visible."
Clear flours are further categorized into two sub-classes: first clear and second clear. First clear possesses a slightly higher level of quality.
The end of the milling process is where the final extraction of endosperm from bran takes place and produces low-grade flour. At this stage of the milling process, high levels of bran in the flour are unavoidable.
Straight flour is, as its name implies, a straight collection of all the flour from the milling process. It includes all of the fractions that would otherwise be separated in the three previous classifications.
Flour treatment. Once flour is extracted from grain, flour mills can perform certain further processing steps that will affect performance. These include bleaching, maturing and malting.
Bleaching frequently is done with benzoyl peroxide, which does nothing to the flour except whiten it. Bleaching with chlorine gas not only whitens flour, it increases the absorption properties of the flour's starch granules and strengthens the gluten. Chemically leavened products - cakes, in particular - depend more on starch than gluten for gas retention and volume. In fact, high-ratio cakes, which contain more sugar than flour, cannot be made without using chlorinated flour.
During storage, flour naturally whitens due to air oxidation. Other changes during this maturing stage improve the flour's performance. In order to avoid long-term storage to mature flour, many mills apply chemical maturing agents. These include oxidants such as azodicarbonamide, acetone peroxide, chlorine dioxide and potassium bromate. The latter is probably the most widely used by U.S. millers.
Because potassium bromate has been identified as a potential carcinogen, it is banned in the European Community, where bakers must seek alternatives. Because they see the potential for a future U.S. ban, many domestic companies also are using other maturing oxidants. When seeking such alternatives, consumer demand has further pushed companies to try and avoid unfamiliar chemical-sounding ingredients. Ascorbic acid (vitamin C) is a popular option. Certain enzymes combined with ascorbic acid are another. The enzymes help to counteract how ascorbic acid lengthens mix times, decreases oven spring and firms a product's crumb.
ConAgra, Omaha, NE, recently developed another option for maturing flour. The process involves treating flour with heat in the presence of air to accelerate oxidation without the use of chemical additives. The company has patented the process and is currently producing test quantities of the flour in a new pilot production facility.
All wheat flour is deficient in (-amylase enzyme. This results in lower bread volumes and more extensive staling. Malted barley or malted wheat flour are common sources of enzyme supplementation.
"Adding malted flour to a formula improves the yeast fermentation, which enhances crust color and volume of the finished product," says Willyard.
More mortar
In addition to flour as the main structural component and water as the primary solvent and plasticizer, other ingredients also help build the structure of bakery-foods. Salt, for example, not only adds dimension to the taste of baked foods, but it makes dough stronger, possibly by shielding charges on the dough proteins.
"Other ingredients, such as fats, sugars and eggs, can be used to modify a product," says Schierioth. "These are the windows and the duct work. The framework and building blocks are there, but it's these other ingredients that come in to provide the uniqueness."
Nevertheless, in the case of fats and sweeteners, structural benefits also are provided in addition to uniqueness.
Sweeteners, for example, are added for several functional reasons in addition to sweetening. In yeast raised products, they provide a source of fermentable carbohydrates which assist in both initiating and maintaining yeast activity. Sweeteners also help smooth and soften the texture, grain and crumb of many products. By being hygroscopic and lowering water activity, they can extend shelf life.
Crust color requires sweeteners of some sort for both coloring mechanisms. The first mechanism is caramelization which, of course, is simply not possible without sugar. The other mechanism is the Maillard browning reaction which requires reducing sugars - such as dextrose, levulose, lactose and maltose - to interact with the flour protein to generate color. Similar reactions also create substances that contribute to flavor and aroma.
Other types of bakery products have additional need for sweeteners. In cookies, the type of sweetener and its particle size affect product spread. Like sweeteners, fats contribute far more than organoleptic properties to bakery foods. In nearly all bakery products, fats extend shelf life by guarding against moisture loss. Fat crystals also promote dough and batter aeration to not only enhance volume, but to create a more even cell structure. In items like croissants and puff pastry, fats are rolled in-between layers of dough and are an essential structural component. Because of the number of different functional properties in various bakery items, fats have, over the years, been specialized to a high degree.
"Years ago, bakers had a limited array of fats. Now, they have a full composite," says David Taylor, director of technical service for Bunge Foods, Fort Worth, TX. "You can buy a shortening that is formulated for nothing but cakes. It contains emulsifiers designed for the needs of cake production and it can't be used for icing. At the same time, fats formulated specifically for icings make poor cakes.
"Fat and oil suppliers have also learned to make shortenings with a wide plastic range so the baker can work with it at a wide range of temperatures. This makes them somewhat stable over the course of a year, so they work just as well both in winter and summer," Taylor continues.
Because of the complexity of this ingredient category, Food Product Design devoted an entire Design Elements feature to the topic of fats and oils in bakery products in its November 1993 issue. In general, though, product designers must answer certain questions in order to determine what fat is going to be used.
"Determine how the finished product should eat and its structure. This, then, becomes the basis for selecting the fat system," says Taylor. "Do you want it to have a certain richness level? What physical characteristics should it have? Do you want it slightly oily to the lips or do you want it to release only in the mouth?
"The structure of the product also must be considered. Determine how much of it the fat should deliver. In puff pastry, the structure comes primarily from the fat that is in-between the dough layers," Taylor continues.
When working with a fat supplier, food designers should tell the supplier the finished product criteria. The supplier then will be able to work backward to determine the fat system that will do the job.
"If we're looking at a cookie, for example, you may want the cookie to spread to a certain degree," says Taylor. "Spread is a major function of fat, as well as flour and sugar. If you want a certain volume, you're going to need a certain amount of creaming. To get this you'll need a good portion of oleic acid in the fat system. This will give you the air cell and will help the cookie to build more volume."
Giving the product a lift
With the basic elements of structure in place, the designer next will have to select the means by which those carefully crafted cells will be expanded. This is the function of a product's leavening system. Leavening can be achieved in several ways. Incorporated air can expand with heat to swell the cell structure of a product such as angel food cake. Water also can act as a leavening agent by expanding when it turns to steam in the oven. The most common means of leavening, though, are yeast and chemical leavening systems.
Yeast is a single-cell plant that generates carbon dioxide by fermenting sugars. More than 600 identified species of yeast exist, yet only one, Saccharomyces cerevisiae, is used in baking to any extent. This doesn't mean that no selection is available with yeast. By controlling growth conditions such as temperature, nutrition and aeration, yeast suppliers have created several thousand strains of Saccharomyces cerevisiae. Each of these strains differs in many ways, such as how fast they'll grow, how tolerant they are to high sugar levels and if they are resistant to calcium propionate.
"A typical type of yeast in the United States will be a strain having an intermediate resistance to calcium propionate and sugar," says Jan van Eijk, a bakery technologist with Gist-brocades Food Ingredients Inc., King of Prussia, PA. "Some yeast has a high resistance to sugar. This high resistance version will have low gassing power, but will be the yeast of choice in high-sugar products."
At the other end of the spectrum are yeasts for lean doughs, which have no such tolerances to sugar and calcium propionate. These do, however, have the highest activity in a low-sugar/no-sugar, no calcium propionate dough.
In addition to the formula, yeast selection must take the process into account. The two-stage fermentation, sponge-and-dough method of bread production, for example, requires a slower yeast that will retain sufficient gassing power through the final proof. On the other hand, straight doughs need a fast yeast that can work quickly to give good initial oven spring.
After determining the necessary formula and process tolerances, a designer will then have to select the proper form of yeast. In general, yeast is available either fresh or dry with several different configurations available under each category.
Fresh yeast is available as cream yeast, granular yeast and compressed yeast. Cream yeast is a liquid containing approximately 20% solids. It is delivered to the production facility in bulk and is useful for systems that require automatic metering. Using cream yeast requires that the production facility be located within a certain proximity to the yeast supplier.
"There also are cost savings because taking cream yeast to compressed requires additional manufacturing costs and packaging," says van Eijk. "For the large bakeries, the cream yeast is the system to shoot for."
Granular and compressed yeast are both made from cream yeast by increasing the solids to 30%. As their names imply, granular yeast is crumbled into granules and packed into bags, while compressed yeast is extruded and formed into a cake, which is subsequently wrapped.
Compressed yeast is the starting material for dry yeasts. Rather than being extruded into blocks, the yeast is extruded through a screen to yield thin, long strands which are broken up, dried into small particles and packaged. In addition to standard active dry yeast (ADY), dry yeast is available as protected active dry yeast (PADY) through the addition of emulsifiers and antioxidants. PADY is more stable than ADY, but neither one requires protective packaging.
Instant yeast contains added emulsifiers and is produced through a drying method that increases its activity. It does require protective packaging, but requires lower dose rates than either ADY or PADY, and it is often considered the best alternative to fresh yeast.
"Industrially, the compressed yeast is used most," says van Eijk. "Although the performance is the same for each, dry yeast costs more to use because going from compressed to dry involves the additional processing step of drying. Drying not only drives costs higher, but causes the yeast to lose a small amount of activity. The packaging also is more expensive because dry yeast must be packaged under nitrogen to avoid contact with oxygen."
While selecting yeast may seem like a simple matter of cost and convenience, different forms of yeast can have a functional affect on certain products. For example, yeast helps develop gluten and affects dough rheology in addition to providing leavening. An instant yeast will produce a dough that is more slack than fresh yeast because it releases natural reducing agents during rehydration. Depending on the use level of the yeast, this may actually shorten the required mixing time for gluten development - a big advantage in straight dough systems.
The right chemistry
Cookies, muffins, cakes and similar products rely on a chemical reaction to produce leavening gases. Besides tradition, one reason for the use of chemical leavening rather than yeast is the previously discussed rheological changes that yeast can have on a dough. Such effects would be inappropriate for most chemically leavened products.
Chemical leavening requires combining a leavening base (usually a bicarbonate) with an acid (such as monocalcium phosphate or sodium acid pyrophosphate). Once heat and moisture are applied, an acid-base reaction occurs, which yields carbon dioxide gas, moisture and a residual salt, in the case of sodium bicarbonate.
Sodium bicarbonate is, perhaps, the most commonly used leavening base. It's inexpensive and easy to use, it is non-toxic and contributes little taste to finished products. The other most commonly used leavening base is ammonium bicarbonate. Unlike sodium bicarbonate, ammonium bicarbonate yields three gasses through thermal decomposition when heated: ammonia, carbon dioxide and water. Because of this ammonia content, ammonium bicarbonate should only be used in low-moisture products. If it's used at moisture levels above 2 to 3% the flavor of the retained ammonia will be detectable.
Potassium bicarbonate and sodium carbonate also can be used as leavening bases. Potassium bicarbonate, however, is hygroscopic and may tend to contribute bitterness to delicately flavored products. Sodium carbonate is almost never used because its alkalinity is so high.
While the effects are most obvious during baking, chemical leavening actually occurs in stages. Reactions begin during mixing, continue through any floor time or handling, and, finally, in the oven. For this reason, how a product is made will directly impact the selection of the chemical leavening system, as will the nature of the product itself.
What lends this flexibility to the system will be the selection of the leavening acid.
"You can change a product's characteristics so much just by modifying the leavening system," says Schierioth. "By going through a whole series of acids and bases, you can come up with about as many variations on the product."
While all leavening acids will neutralize the base, they do so at varying rates. How the rate of gas evolutions fits with the product and process will determine the type of acid used. For example, anhydrous monocalcium phosphate releases about 20% of the available carbon dioxide gas during a 2-minute mix cycle, 40% more during a 10- to 15 minute floor time, and the rest in the oven, according to information from Rhône-Poulenc Food Ingredients Div., Princeton, NJ. The same acid in a monohydrate form, however, will release 60% of the gas during mixing, little or none during floor time and the rest while baking.
Once the desired reaction rates point to the type of acid, the neutralizing value will determine the amount required. The neutralizing value of a leavening acid is the number of pounds of sodium bicarbonate that can be neutralized by 100 pounds of acid. For example, 138.9 pounds of a sodium acid pyrophosphate with a neutralizing value of 72 are required to neutralize 100 pounds of sodium bicarbonate. Adding the appropriate amount of acid is critical because if too much remains in the finished product, it will contribute an undesirable tart flavor. Too little, and the product may have a soapy, alkaline flavor.
Process particulars
After structure and leavening, the third leg of the stool holding up a baked product is the process. In fact, even the best designed formula can fail because of a process variation. While full details of how processing affects a product will have to wait for another feature story, here are some of the more critical points to keep in mind at the various processing stages.
Mixing, as previously mentioned, is a critical part of gluten development for yeast-raised products. By incorporating air, it also creates the cellular structure, which is later expanded by the leavening system. As with many things, though, designers must avoid too much of a good thing.
With yeast-raised doughs, gluten development reaches an optimum peak. After this point is reached, further mixing serves no purpose and will break down the dough into a wet, sticky mass. One suggested reason for this is that extended mixing causes the long gluten molecules to line up in the direction of the mixing action.
This theory itself breaks down because the over-mixing phenomenon will not occur if dough is mixed under nitrogen gas. A more plausible explanation is that oxidants of various types induce breakdown by oxidizing S-H groups on the gluten molecule. Without these, the protein becomes stressed and begins a chain reaction wherein more and more S-H bonds break. The stronger the protein, the fewer S-H groups to be acted upon by oxidants and, subsequently, the more resistant the flour is to overmixing.
In a chemically leavened system, overmixing simply adds too much air to the system. This has many potential detrimental effects. For one, the volume will be off because of the lower specific gravity. Too much air also may change the rate of the leavening system reaction. For this reason, cake and muffin batters are mixed to a pre-determined specific gravity. While this also is true for some cookies, many cookie doughs are mixed only to the point where the ingredients are combined.
After mixing, the way a dough is handled must be specified in order to avoid product variability. Fermentation times, floor times and the like must be consistent or the amount of gas produced during proofing and/or baking will change. In most cases, the needs of the production facility will require more time than has been allotted during development. Try to determine what will be required before formulation. Changing a leavening system or reformulating to make a more time-tolerant dough will only waste time during production scale-up.
Turning up the heat
When baking at home, getting the product to the oven is the end of the process because there is little to do but set the correct temperature. Industrially, how a product is baked and with what equipment it is baked can change a product as much as reformulation.
Because industrial ovens are designed for mass production, they consist of a continuous baking surface passing through a heated chamber. This allows different temperatures to be applied at different phases of the baking cycle. How this is set up will directly affect a product's volume, spread and crust color. For example, a little extra heat can be applied in early zones to promote rapid oven spring for a larger cell structure. Subsequent zones might be cooler to avoid product collapse while holding the product volume and allowing the structure to set. The final zones might return to slightly higher temperatures to contribute color and to drive off moisture to the desired level.
In addition to temperature, how heat is applied can affect a product. During baking, heat is transferred through three primary mechanisms: radiation, conduction and convection. Radiation is the heat that is transferred from the heating source to a product through space. Conduction is heat transferred through direct contact with a hot body, such as the baking surface. Convection is the heat transferred by a moving fluid - air and steam, in the case of baking.
Commercial ovens offer various combinations of heat application. A direct gas-fired oven applies heat like a home unit through radiation. Conduction also occurs through the baking surface. To some degree, convection also occurs due to the natural rising of air and steam. Recirculating ovens and impingement ovens increase the rate of heat transfer through convection by moving heated air in a controlled fashion. Depending on the type of oven, heat application can be controlled by adjusting vents, air inlets and burners.
The combination of temperature and application settings is known as the oven profile. The designer will need to determine the profile that produces the optimum product. As with mixing and handling, consistent profile settings will be critical to consistent finished products.
Casting the spell
While only a brief overview of baking technology, all of this still may strike some readers as an awful lot to keep in mind just to create a cookie. But, familiarity with the elements of structure, leavening and processing is required in order to allow designers to be creative. At the same time, designers shouldn't feel locked in by baking conventions.
"People shouldn't be afraid to think beyond the rules," says Schierioth. "Some old books had rules for balancing tougheners and tenderizers - like when you raise sugar, you must raise egg. I've learned, though, that formula balance is, by and large, something nice to know, but you can't get locked into it. When you develop a new product, you have to have the creativity."
Remember, though, that a creative formulation effort still should be defined, specified and optimized scientifically. Compared with other food products, many bakery processing lines are very inconsistent. This has, in the past, been widely accepted because satisfactory bakery products can be obtained without perfect conditions. This does not, however, fit in with current trends for total quality.
"Sometimes the product is less than perfect, but the range of acceptance is typically a little broader," says King. "With a better line and a little more time, you can tighten this. You can't achieve further improvements with, say, margarine because you already must have everything optimized to a high degree. One day, the baking industry will be the same. At least it has the potential to be."
When it does happen to the baking industry, it will consummate the marriage between science and magic.
|
Email this article
Add a comment
Printer version
Order reprints
RSS Feed
Bookmark article