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July 1, 1995
Mastering the Morning:
By: Scott Hegenbart
Although it has been derided for its fat and cholesterol content, many people still attach a certain degree of nostalgia to the traditional "big breakfast" of bacon and eggs. In truth, however, most U.S. consumers don't start every day with this dish. This isn't because they've become so health conscious as much as they are simply too time-pressed most mornings to prepare such a meal. Even the instant forms of popular hot cereals seem to require too much preparation effort. (This author even confesses to thinking this now and then.) Fortunately, ready-to-eat breakfast cereals provide morning nutrition in the time it takes to splash milk into a bowl.
In the century or so since they were originally created, breakfast cereal popularity has grown to the point where they encompass virtually an entire aisle of a typical grocery store. The variety of shapes, sizes and flavors available is incredible considering that breakfast cereals all start with the same basic ingredients - grain, sweeteners and flavorings. How these basic components are combined and processed, however, greatly contributes to cereal variety.
Many breakfast cereals are still made by traditional methods handed down from the last century. Others are processed by variations of these methods. Still other cereals are made using extruder technology developed in the 1970s and refined during the 1980s. Understanding the basics of how these processes work gives product designers the foundation for formulating new breakfast cereals.
Flakes made from either whole grain or pieces of whole grain are the original ready-to-eat breakfast cereal. The first of these was made from wheat by Dr. John Harvey Kellogg in the late nineteenth century. (His brother, William K. Kellogg, actually commercialized the product and started the company that still bears the family name.) The dry milled grains used for traditional flaking include wheat and rice, which are processed whole; and corn, which is processed as specially sized pieces known as "flaking grits."
The grain is first mixed with a solution of ingredients including sugar, malt and salt in water. This is then loaded batch wise into a steam-heated, rotating pressure cooker. Once cooked so a specific moisture content in the grain is reached, the batch is discharged onto a conveyor which carries it to a machine that breaks apart the large lumps of cooked, swollen grain back into individual grits.
The individualized grits will contain too much moisture for flaking at this stage. Consequently, they are dried under controlled heat and humidity to a level of 10% to 17%, depending on the grain. In order to equilibrate moisture both among the many particles as well as throughout each individual particle, the dried grits are held for a several hours in a process known as tempering.
After tempering, the grits are finally ready for flaking. The grits pass through two large, metal rolls which flatten them to the desired thinness. Because the pressures are so great, flaking generates tremendous heat. This heat is capable of accumulating to the point of actually cooking the flakes so they stick to the rolls. To avoid this, the flaking rolls are hollow and contain spiral channels through which cooling water is passed.
The flattened flakes are finished with a final toasting step. Specialized flake-toasting ovens do this by suspending the flakes in a hot air stream by means of either a rotating perforated drum or a vibratory conveyer. The finished flakes have a moisture range of from 1% to 3%, again depending on the grain.
Whole grain, almost exclusively wheat, is traditionally used for making shredded cereal biscuits. Unlike flakes, this process starts by cooking the cleaned, whole wheat in water with no other ingredients added. The finished moisture content will be significantly higher than wheat cooked for flaking - about 50%.
After cooking, the grain is cooled and placed in holding bins for tempering. In this case, tempering does more than simply equilibrate moisture within both the batch and individual kernels. The process allows the cooked wheat kernels to become firmer, making subsequent processing easier.
As with flaking, shredding itself is achieved by passing the tempered grain between two rolls. These rolls, however, are much smaller than flaking rolls and one roll will contain grooves to yield the web of shredded grain. One pair of rolls will produce one layer of the shredded grain biscuit. Full-size biscuits require around fifteen or more pairs for enough shred layers.
Once enough shred webs are layered, the mass passes through a cutter. This device's edges are not sharp enough to actually cut, but compress the web into individual biscuits that are joined together. The biscuits then pass through a band-oven for baking down to a moisture below 5%.
Traditional puffing yields a cooked, expanded grain kernel through one of two methods: Oven puffing and gun puffing. Oven puffing is limited to rice or corn since they are the only grains that, at the right moisture level, will puff with the simple application of heat. Gun puffing will work with both of these grains as well as wheat and oats.
The cooking step for oven puffing is similar to that of flaking. The grain is first mixed with water, malt, sugar and salt. Next, the batch is pressure cooked with steam to a predetermined moisture. At this point, the similarity to flaking ends.
After cooking, the grain is subjected to a multi-stage drying process. The first stage partially reduces the grain moisture. This is followed by tempering to fully equilibrate the moisture. Following this, however, the grain is "bumped" by passing it through flaking rolls set at a much wider gap than that used for making flakes. Bumping is required for maximum expansion and is thought to function by partially de-stabilizing the kernel's internal structure.
Last, the grain is dried a second time to a final moisture of around 10%. The prepared grain is finally passed rapidly through an extremely hot oven where it expands and is toasted.
Rather than using heat to expand moisture within the grain, gun puffing uses a sudden drop in atmospheric pressure. An example of how the process works can be found in the traditional single-shot cereal puffing gun.
Water and grain are added to the preheated gun. After the lid is closed and locked, the gun is heated with rotation to convert moisture to steam and to pressurize the chamber. Once the desired pressure of around 200 psi is reached, the heating process is stopped and the gun aimed in the direction of a collection bin. A firing system then rapidly opens the lid. This drop in pressure causes the steam within the grain to expand and explosively flings the expanding kernels into a collection hopper.
Advances in gun design have increased the efficiency and yield of cereal puffing. Multiple-shot guns use the same charging equipment and collection hopper for several guns mounted on a rotating wheel. Continuous cereal puffers also exist where the grain is passed through a pre-pressurized chamber and individual kernels are released into atmospheric pressure through a special valve at the opposite end.
After puffing, the cereal isn't finished. It first must be screened to remove unpuffed grain, broken kernels and bran. The product also must be dried from about 6% to about 2% moisture.
Technically, many of the breakfast cereal forms already discussed are baked in some fashion to toast them. For the purpose of this article, though, baked cereal refers to products made through methods more closely resembling traditional baking technology.
One well-known cereal uses bread-baking methods to yield toasted whole-wheat nuggets. Here, whole wheat flour is blended with barley, water, sweeteners and yeast to make very dense bread-like loaves. Once baked to a very low moisture, the loaves are shredded. The shreds are further baked, toasted and reground into nuggets to form the final cereal.
Another popular baked cereal is granola. This product starts with rolled oats to which water, vegetable oil, sweeteners, nuts, dried fruit and other various ingredients are added. The resulting dough-like mass is spread onto the band of a conveyor oven and is toasted until the moisture is below 3%. Once baked, the layer of granola is broken into bite sized pieces and packaged.
A final example of a baked breakfast cereal uses production equipment designed for cookies. Here, flour, shortening, sweeteners, rolled oats and water are blended into a crumbly dough suitable for forming on a rotary moulder. This machine is the same one used to make base cakes for sandwich cookies.
In the rotary moulder, dough is fed between two rolls - one roll is grooved and presses the dough into the other which bears a cylindrical die. As the die rotates, it releases the pressure-formed dough pieces onto a belt. This belt feeds the formed pieces to the band of a conveyor oven which bakes the pieces to a final moisture of about 2.5%.
Through ingredient selection and processing, whole grains yield many varieties of breakfast cereals. The growth of extrusion into breakfast cereal processing, however, has further widened the possibilities because, rather than using whole grain, flour or meal can be the grain source. This allows the blending of different grains into unique cereal pieces. Extrusion also has made production more efficient by combining several processing steps into a single, continuous unit.
An extruder consists of one or two screws that rotate in an enclosed barrel. The turning of the screw(s) will serve many functions: it mixes and shears the raw materials; it pressurizes the product mass; and it moves the product along the length of the barrel to be extruded through a die of the desired shape.
Along the way, different zones of the barrel may be heated to cook the product mass, or cooled to temper it. Water and/or solutions of flavorings and colors also may be metered into the product as it passes through various zones of the barrel. Once extruded from the die, the dough is cut into pellets which are then directly processed like whole grains in flaking, shredding or gun-puffing equipment.
Flaking. Extruded flakes start by adding the grain (as whole grain flour, meal or, in the case of wheat, whole kernels), sweetener, salt, water and other raw materials directly to the extruder. At the feed end, little heat is applied to the barrel so the ingredients may first be blended without cooking. If the product is to be made with whole wheat kernels, the screws themselves may even be specially designed to ensure that these are crushed. Next, the material passes through the section of the barrel to which heat is applied for cooking. After the cooking section, the product passes through a cooling section just before extrusion through the die. This cooling step prevents the cut pellets from expanding and flashing off moisture as they exit the die. Ideally, the process should be controlled so that the moisture of the pellets requires no drying or tempering. The pellets may then be directly fed into equipment to be flaked and toasted in the same way as a batch of cooked whole grain. Shredding. As with extruded flakes, the grain source for extrusion shredding can be flour, meal or whole grain kernels. The extrusion processing also is pretty much the same with the exception that even pellet sizes are not as critical since they are going to be shredded anyway. One of the main advantages of extrusion processing for shredded products is efficiency - once extruded through the die, the pellets may be directly shredded without further drying and tempering. Puffing. Again, the cooking process through the extruder is similar to that of product that is to be flaked or shredded. One difference, however, is that the extrusion die usually will be designed so the pellet yields a unique shape after puffing because it won't be flattened or shredded. Another difference is that the moisture of the cooked, shaped pellets is usually too high after extrusion (around 22%) for optimum puffing. Consequently, a drying and tempering step still must be performed to equilibrate the pellet moisture content to around 10%. After tempering, the pellets are simply puffed as if they were prepared whole grain. Screening next removes broken pieces, unpuffed pellets and fines and the finished cereal is then dried to around 2% to 2.5% moisture. Creating pellets for further processing is not the ultimate in efficiency that extrusion can provide. Modifying the equipment and process allows the extruder itself to directly expand the cereal. As previously noted, ordinary cereal pellet extrusion requires a cooling section in the barrel to prevent product expansion upon exiting the die. For direct expansion, on the other hand, this is the desired result. To achieve this, the final zone in the extruder barrel will be used to heat the product. Modifications to the screw design will work with the heat in this zone to build pressure. The added heat and pressure of this zone will cause the piece to expand significantly when it exits the die into atmospheric conditions. Once leaving the die, the piece may either be cut immediately, or allowed to cool slightly first. Immediate cutting when the piece is warm allows the edges to become rounded and the cereal will closely resemble a gun puffed pellet. After a period of cooling, the structure of the extruded product will have had time to partially set and cutting will leave clean, sharp edges to the piece. The choice will depend on the product concept. If, for example, the cereal is a co-extruded piece with two differently colored doughs in a distinct pattern, the latter option provides maximum visibility. Formula foundation At this point, breakfast cereal quality may seem very process dependent. Selecting ingredients for cereal formulations, nevertheless, is still critical for quality and variety in the finished product. Proper ingredient selection also requires an understanding of the process in order to know the conditions the ingredients must endure. The two elements of breakfast cereal creation are highly intertwined. Grain is, of course, the primary ingredient in breakfast cereals with corn and wheat being the most predominant. Most corn for breakfast cereals is used for making flakes and comes from yellow corn that has been dry-milled to remove the germ and bran. The remaining endosperm is ground to a very coarse grit for flaking. Puffed corn is make from extruded pellets that are formulated with more finely ground corn meal or corn flour. These forms also are used in mixed-grain extruded cereals. Wheat is classified into varieties such as white or red, depending on the color of the bran; and hard or soft, depending on the strength of the gluten. Durum wheat is extra hard and normally is used for making pasta. Any of the varieties can be used in cereal, depending on the color and structure requirements of the finished product. Durum wheat, for example, has large kernels and a light bran color yielding large, attractive puffed wheat. The color, however, is not so critical because most wheat is pearled prior to puffing. This is done because the bran doesn't expand with the kernel and simply falls away and contributes to fines that must be screened out later. Color also is not so critical to flakes because the added malt and sugar contribute a desirable brown color after toasting that conceals whether the product is made from white or red wheat. In order to flake thinly and evenly, though, flakes are generally made from soft , wheat varieties. Both softness and light color are important to , shredded wheat products.Consequently, whole-grain shredded wheat products are generally made from soft white wheat. Like wheat, oats are available in red and white varieties, but only white oats are milled for human consumption. Milling removes the outer hull to yield a kernel known as a groat. Groats are further processed in one of four ways. Whole groats may be steamed and rolled to make regular rolled oats. Quick-cooking oats hydrate faster because they are thinner. They are made by first cutting the groats into three or four pieces prior to steaming and rolling. Instant oats are cut into still smaller pieces after which they are steamed and rolled. Finally, the groats may be ground into oat flour. Rolled, quick-cooking and instant oats are, of course, sold as hot breakfast cereals. They also are used in formulated breakfast cereals, such as granola. In this case, the size of the finished cereal piece and the desired visual impact of the oats will primarily determine the oat selection. (Some size variations also will be available within the three types of oats.) Oat flour is used for extruded oat and multigrain cereals. Rice for breakfast cereals is first milled to remove the outer hulls. The resulting brown rice is then pearled to remove most (or all) of the bran layers. This white rice is then sized into four grades. The first consists of unbroken kernels known as "heads." These are used for puffing. The next grade, the second heads, are made up of the larger broken kernels and are used to make flakes. The smaller broken kernels make up the third rice grade known as brewer's rice. Brewer's rice is often used for formulated extruded cereal as is rice flour made by grinding the second heads. The last grade consists of the fines screened during milling. Barley, like rice, is milled to remove the outer hull and pearled to remove the bran when used for cereal. It may be flaked, or ground into flour for formulated cereals. The most common cereal use for barley, however, is malted as a flavoring material. Malting is a controlled germination that enhances the barley's flavor and enzyme activity. The grain is first steeped to absorb equilibrium moisture for germination. Next, germination takes place in a special bed over a period of four to five days. Last, the sprouted barley is kilned to remove moisture from the "green" (undried) malt, and promote the browning reaction that produces the malt flavor. Once hulled, the finished malt is milled to either a meal or flour. Another option is for the malt to be extracted with water and either concentrated to a syrup, or dried into a powder. Whatever the form, the finished malt may either retain its enzyme activity (diastatic malt), or not (non-diastatic malt). Because breakfast cereals use malt primarily for flavoring, nondiastatic malt is preferred to prevent the enzyme from causing an undesirable softening of the finished piece. In whole-grain cereal processing, malt syrup is generally diluted with water and added to the cooking stage. For formulated extruded products, malt addition is more flexible. Malt powder or flour may be added with other dry ingredients at the feeder end, while diluted malt syrup may be metered into the barrel during processing. This latter method affords the option of adding the malt later in the process for milder flavor and color development. Sweeteners for function, flavor When consumers think of sweeteners in ready-to-eat cereals, they often picture only pre-sweetened products targeted to children. In fact, sweeteners perform numerous functions in many different types of breakfast cereal, whether they are formulated in the product itself or applied to the surface as a frosting or glaze. As an integral ingredient, sugar is a fundamental ingredient in both whole-grain cereal processes and formulated/extruded ones. Although flavor is the most obvious contribution, sugar helps bind the grain mass together, contributes to the texture of the finished cereal, and is necessary for proper browning. Sucrose is the in-formula sugar most often used in cereal production - usually in a 67° Brix liquid form. Invert syrup is occasionally used where greater sweetness and color development are desired. This also is true for corn sweeteners. Although important in many formulas, the major use of sugar in breakfast cereals is as a surface coating. Such sugar coatings do more than appeal to the sweet tooth. In certain puffed products, the sugar coating helps prevent the cereal from absorbing excess moisture. In others, the coating is a critical structural component for a more delicate cereal piece. As with in-formula applications, sucrose is the predominant sugar used because it contributes less viscosity making it easier to spray onto finished cereal. Because it is a disaccharide, sucrose also will not be as prone to browning when the coated cereal is dried. Finally, sucrose readily crystallizes into a desirable white frosting. For hard, clear sugar glazes, invert syrup, corn syrup or honey (which is primarily invert syrup) are added to the sucrose solution. These sweeteners function by inhibiting sucrose's crystal growth to yield a smooth amorphous coating. On the micro side Grain, sugar and malt may be the primary macro ingredients of breakfast cereals, but ingredients used at lower levels also are very important. Falling just after the "top three" cereal ingredients in quantity, salt is necessary in many breakfast cereals. It acts primarily as a flavor enhancer to blend the flavors of the various components together and form a unique flavor profile. In addition to the natural flavors of the grain, sugar and malt, many specialty cereals - particularly those targeted to children - require added flavoring ingredients. The heat and pressure of breakfast cereal processing, however, seems almost tailor-made to cause volatiles in these ingredients to flash off. The extreme conditions in extruders seem to be particularly prone to this sort of flavor loss. In the case of puffing or direct-expansion extrusion, flavor components may actually be steam-distilled out of the product. A simple solution would seem to be adding an overage of flavor ingredients to the formula. Unfortunately, various flavor volatiles frequently are lost in different degrees throwing the flavor's balance off. Fortunately, methods both simple and sublime provide solutions to this challenge. First, how the flavor is added can be modified. For example, instead of adding the flavor to the formula, it can be added to the sugar coating deposited after most of the more rigorous heat treatment is completed. Because finished, sugar-coated cereals are simply dried at relatively low temperatures, loss of flavor volatiles will be minimal. If the piece is not to be coated after processing, designers can try adding the flavor as late in the process as possible. For example, extruded products can have the flavor piped into the extruder barrel in the cooling zone after cooking. Some flavor may still be lost on subsequent processing, but at least the flavor's exposure to heat and pressure has been significantly reduced. Naturally, this solution isn't as effective for direct-expansion products that have no cooling zone prior to extrusion through the die. Last, product designers can work with a flavor supplier to create a flavor designed to compensate for the process stress. Newer encapsulation technology can help flavor volatiles withstand high heat processing. Another possibility is to study which volatiles are most susceptible to flashing off and having a flavorist design a flavor with overages of these components so that the finished product's flavor profile is still in balance. Visual cues In a traditional whole-grain cereal process, the combination of grain, malt and sugar creates a desirable golden color in the finished product. In formulated, extruded cereals, however, the more extensive mixing stress may result in a dull, sometimes grayish, color. The addition of a coloring ingredient helps to overcome this. These may include annatto extract, beet powder, FD&C Yellow Nos. 5 and 6, FD&C Red 40 and FD&C Blue No. 1. Lighter hues of caramel color are a common solution because they are made by caramelizing sugars. Not only does this make hue of caramel color correct, but the ingredient already has been subjected to severe heat stress during its manufacture and won't be affected by the high heat of cereal processing. Specialty cereals for children, on the other hand, use a rainbow of bright colors. Although many consumers would like to see non-certified ("natural") colors used in these products, the simple truth is that many cannot tolerate the processing sufficiently to provide the extreme color intensity desired in children's cereal. In fact, some FD&C colors have difficulty holding up the pressure and heat of cereal manufacturing. Still, one look at the cereal aisle shows that success is possible. In addition to color, visual appeal (as well as textural interest) can be added to cereal through the use of add-in ingredients such as nuts, dried fruit pieces, marshmallows and so on. Small pieces may actually be added to surface coatings to enhance the piece itself, or larger ones blended into the finished cereal. Whatever the method, the moisture and water activity of such additions is critical and must be balanced with that of the cereal. If not, moisture can transfer from the added piece to the cereal and make it soggy. Other factors to consider include the density of the piece. While a whole almond would contribute greatly to visual and textural appeal, they would all end up at the bottom of the cereal box by the time it reached consumers. Sliced or slivered pieces will be lighter in density and tend to stratify to a lesser degree. Dried fruits may tend to clump together. This is avoided in some fruit pieces with a light dusting of sugar. Other pieces, such as raisins, may be kept free flowing with a thin coating of either high-stability oil or glycerin. Boosting nutrition Breakfast cereals are commonly fortified with vitamins and minerals. Two reasons account for this common practice. 1) Most grain sources used to create cereals have been milled to remove the germ and, thus, their vitamin content is reduced. 2) Consumers frequently ignore suggestions that cereals are "part of" a balanced breakfast and look for the cereal to be a balanced breakfast. The challenge, however, lies in the fact that cereal processing involves a great deal of heat and many nutrients are sensitive to heat degradation. So much so, that simple overages are often cost prohibitive. Several approaches may be used to fortify breakfast cereal without destroying the desirable (and expensive) nutrients. First, the more heat stable nutrients - such as the minerals, riboflavin and niacin - can be added to the base formula while heat-sensitive ones - like thiamine and vitamin A - are sprayed onto the finished product. Another option is simply to have all the vitamins and minerals in one premix that is sprayed on after processing. Whatever the method chosen, manufacturing and quality assurance are greatly simplified by the use of pre-blended nutrient pre-mixes shipped with a certificate of analysis. Vitamins and minerals are added at such small quantities compared with other cereal ingredients that it often is simply not worth the effort to formulate and test nutrient pre-mixes in house. In addition to heat, vitamins A and D also are highly sensitive to oxidation. Whether formulating an in-house pre-mix or specifying one from a supplier, make sure it contains an antioxidant to protect these nutrients. The spray itself can further add protection if it contains sucrose (at least 10%) which will act as an oxygen barrier when the spray is dried. Another helpful option is to spray the nutrients onto the cereal before any frostings or glazes. Ready-to-eat breakfast cereals indeed provide a dizzying array of options for the morning menu. Considering some of the process stresses these products undergo, striving for still more unique products in this category can present a tremendous challenge. Fortunately, understanding these processes and how they affect ingredients helps keep product designers from going, well... flaky. Sweet Dreams It's common to hear consumers talk about how they avoid those "sugary breakfast cereals" for both themselves and their children. Cereal manufacturers acknowledge this consumer desire by touting products as containing "low" or "no" sugar, In fact, researchers have shown that the total sugar content of ready-to-eat breakfast cereals ranges from 0% 50% with many levels represented in between. This certainly offers consumers the opportunity to control how much sugar they eat in breakfast cereals. But do they? Studies demonstrate that most consumers prefer sugar on the cereal they eat. If the product isn't pre-sweetened, they add sugar by the spoonful. Now, a common flatware teaspoon will contain anywhere from 2 to 3 grams of sugar when level. This shoots up to nearly 8 grams if that spoon is heaped. (The "sugar shell" spoons commonly used in the sugar bowl on the table are even larger.) On a recommended cereal serving size of 1 ounce (roughly 28 grams) 8 grams of added sugar translates into 22%. With two heaping spoonfuls, this figure shoots up to 36% sugar. If three spoonfuls are added - as has been commonly observed in children during consumer research - the sugar content is 46%, or nearly as high as the most sugar-laden pre-sweetened cereal. Considering how important sugar is to product texture, color, flavor and nutrition (yes, sugar coatings help protect oxidation-prone vitamins), designers shouldn't be overly concerned about consumer reaction if the formula requires a little sugar. Back to top
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