RTE Cereal Processing

Ready-to-eat (RTE) cereal are the processed cereal grains intended to be consumed easily without any further cooking or processing at the consumer level. These processed cereals are typically consumed along with milk as a main course for a breakfast meal or readily eaten as a snack. Hence, they are also known to be a part of breakfast cereals. Breakfast cereals are of two different kinds – hot cereals and cold cereals (RTE cereals). Hot cereals need to be briefly cooked before consumption at home and therefore are quite less popular compared to RTE cereals. RTE cereals are well-known products today due to the ease of consumption at the consumer level. They are loved by people of all ages due to the availability of wide ranges of flavor, color and are filled with all the important nutritional supplements.

RTE Cereals

RTE cereals were invented a long time before but constrained only for use in some religious beliefs. The American clergyman Sylvester Graham in 1829 invented the well-known Graham cracker (biscuits made from graham flour). Innovations and research continued and in the early 19th century, the Kellogg brothers invented various products such as granola cereals and they were the first to invent precooked flaked cereal. Their success led to the rise of many similar businesses. Even today, Kellogg’s marks one of the highest market shares for RTE cereal products. RTE cereals are served in 90% of American households and hence, constitute large economic importance in the food sector.

Best-selling US Breakfast cereal brands (2015)

RTE cereals are produced from compelling food grains such as corn, wheat, rice, and oats and other classes of ingredients like water, sweeteners (molasses, sugar, corn syrup, etc), macro ingredients that provide flavoring and enhances texture. Micro ingredients are also added to fortify the processed cereals because in some cases all the important nutrients like vitamins and minerals are lost to a great extent. Other particulates and antioxidants can be added to enhance the flavor and shelf life of the product respectively. The amount of all the required ingredients involved vary according to the processing aspects, batch operating parameters, and the desired texture and flavor for the end product. Grains can be cooked in a rotary batch vessel (direct steam injection method) in traditional processing, or they can be pre-processed to obtain flour which can be further cooked in an extruder accordingly.

RTE cereals can be grouped into four general categories:

  1. Toasted flaked cereals, including extruded flakes.
  2. Puffed intact grains (gun puffed and oven puffed), including extruded pellets.
  3. Baked shredded whole grains, biscuits, and extruded grain fractions.
  4. Granola and muesli-type cereals.

Apart from the mentioned above, other kinds of RTE processed cereals include extruded expanded cereals, baked cereals, compressed flake biscuits and filled bite-size shredded wheat.

Processing steps:

  1. Pre-processing of Grains: Grain selection is one of the important steps in pre-processing operations as it affects the taste and final characteristics of the product. Proper harvesting, cleaning, and screening operations take place according to the type of grains being processed and various essential product requirements. For specific applications, the outer layer of bran is removed from whole grains through crushing by metal rolls. Grains are milled into flour for their processing through extrusion cooking.
  2. Blending: Whole grains or flours are mixed with sweeteners, water, salt, flavoring, and fortifying agents as per requirement and batch size to be processed for a single run. 
  3. Cooking: Blended mixture is subjected for cooking through either batch pressure cookers (for whole grains) or cooking extruders (for milled flour). It induces the development of desired texture and nutritional properties. Cooking on a basic note affects the physical properties through gelatinization of starch in grains. Moisture content, temperature, pressure, and batch time play a significant role during cooking operation, and they need to be optimized as per requirement.

a. Batch cooking: Food grains are processed in batch pressure cooking, where steam is injected into the pressure cookers. The batch cooking process involves the formation of lumps and may incorporate uneven moisture content. These changes can’t be ignored, and cereals need to be treated through various other operations like tempering, delumping, drying, etc.

Batch cooker
DumpingCooked cereals are dumped over a moving conveyor belt or spread out over a large area for uniform distribution in subsequent cooling.
DelumpingBreak the loosely held and agglomerated grits for proper circulation of heated air. It also avoids the product from appearing soggy for further processing.
DryingStabilizes the moisture content and result in a minimum of skinning over near cereal surface.
CoolingIt brings the cereals back down to the ambient temperature and stops further cooking that may darken and lose quality during the next processing.
TemperingHolding the grains/grits in large tanks at ambient temperature for a particular amount of time. It equilibrates moisture and flavors in cereals throughout the tank. 
RTE Cereal Processing

b. Extrusion cooking: Extrusion cooking is an HTST process. It incorporates various functions like agglomeration, starch gelatinization, protein denaturation, texture alteration, and shaping in a single operation. There are various types of extruders used in the processing of RTE cereals like a single screw, twin screw, and kneading type extruder. Their applications may vary according to the cost and convenience of operation. Heat is supplied to the barrel for cooking and mechanical shearing homogenizes the operation of mixing and even distribution of ingredients. Die (opening section) extrudes the dough out after complete cooking and a rotating knife cuts the product out in a form of a ribbon. The Die section is responsible for a variety of shapes in RTE cereals. The resulting product may appear dull after extrusion processing as a result of Maillard reaction browning. Therefore, a small amount of natural or artificial yellow color is added to make the final product more attractive and appetizing. Processing parameters are closely monitored to get the desired moisture content and texture for the final product. Hence, in most of the cases for extrusion cooking, there is no need to look after cooling and drying.

Cooking Extruder

Above processing steps more or less are common for the general processing of RTE cereals. Once the cereal possesses the desired properties and moisture content (usually 10-14% w/w), other following steps vary according to end product requirements as follows:

  • Flaked cereals: Flaking is accomplished by passing the tempered grains between two large metal rollers applied under very high pressure. This process flattens the cereals, and their thickness can be varied as per convenience.  Rollers are hollow and heat generated during flaking is mitigated by passing cooled water in the interior sides. A scraper knife is used to remove the flakes and convey them further for toasting operation. Flakes are suspended in a hot air oven that incorporates sloppy ends. Flakes are carried through a vibratory trough where hot air streams push them forward through varying temperature zones. Toasting is done to decrease the moisture content (usually up to 3% w/w) and provide crispness to the final product. Corn flakes, wheat flakes, and rice flakes are some of the well-known flaked cereals.
Corn Flakes
Wheat Flakes
Flaked Rice
  • Gun-puffed cereals: Puffing is an important heat transfer phenomenon where phase shift takes place from water to steam inside the whole kernel grains. Only rice (parboiled medium-grain) and wheat are processed to make puffed cereals where rice doesn’t require any pre-processing action whereas, in wheat grains, the outer layer (bran) needs to be removed through the action of pearling. It can also be possible through soaking the wheat grains in a salt solution that toughens the bran layer which can get break-off easily during the puffing. Cooked grains are heated through gas burners to very high temperatures (300 – 4300 C) where moisture gets converted to steam. It is followed by a sudden high-pressure drop. The puffing gun is sealed with a system operated by cam and lever. The lid is opened so that the internal pressure is released that catches the puffed grains in some vented bins and subsequently fires the gun for the next operation.
The Puffing Gun

In operation for extruded gun-puffed cereals, cooked dough obtained from the extruder is subjected further to a forming extruder which is operated at noncooking temperatures (usually below 700 C). Forming extruder process the dough expansion in parts during puffing that result in different variety of shapes in the final product. However, the moisture content of the final puffed cereal is 24%. Hence, extruded puffed cereals are subjected further for tempering and drying for reducing the moisture content (1-3%) and for homogenized flavoring.

  • Oven-puffed cereals: Oven puffing is done only on rice and corn grains or a mixture of both. These grains can puff in presence of high heat and when the moisture content is stable. Oven puffed cereals follow all the unit operations that are mostly involved after pressure cooking of grains. After the final tempering process, cereals are bumped through a process called bumping. Bumping is just running the cereals through the rollers similar to that done during the flaking process but here only thin flakes are obtained and processed further. The thinner dimensions of bumped cereals help for faster heat penetration during oven puffing. Bumping is again followed by a second drying step that develops a proper balance of moisture content for oven puffing operation. Oven puffing and toasting take place simultaneously after bumping in a fraction of seconds.  Rotary flake-toasting ovens are employed for this operation. Puffed cereals obtained are further cooled and fortified with vitamins and minerals accordingly.
Puffed Grains
  • Shredded cereals: Primarily only wheat grains (white wheat and red wheat) are processed to make shredded cereals. Rice, corn, and other grains can also be processed but they are quite less popular. Wheat grains are cooked and tempered properly. Tempering makes the kernel firmer through retrogradation of starch and it’s necessary for obtaining shreds of good strength which further simplifies cutting and handling. Tempered cereals are passed through rollers (one is smooth and the other is grooved). Grooved roller shreds the cereals in a form of ribbons. These ribbons passed through a conveyor belt where they are piled up in a form of layers. Dimension of grooves may vary accordingly to the shape of shredded cereals required. The shredded cereals are baked, or they can be converted to form large, shredded wheat biscuits with subsequent baking. Large capacity operated rolls or some 10-20 pairs of rolls can be employed to form rectangular shredded wheat biscuits which are cut, compressed, and rotated to alter the size, shape, and texture as per convenience. Shredded biscuits are baked further in a band or continuous conveyor belt oven. Baking incorporates some physical and chemical changes like changes in shape and color, flavor development, and most importantly moisture reduction. Further antioxidants are added, and another fortification is done. Extruded cooked cereals are processed in somewhat a similar way as that for traditional processing.
Shredded Wheat Cereals
  • Granola cereals: Regular or quick-cooking oats are used to make granola cereals. They are blended with various ingredients such as nut pieces, cinnamon, nutmeg, coconut, brown sugar, dry fruits, and some vegetable oils along with water to form a suspension. This dry blend is homogenized properly and consequently spread on the band of continuous dryer or oven. This uniform layer of the mat is baked further at a higher temperature (nearly 2000 C) until the mat is toasted uniformly and moisture content becomes 3% w/w. This mat is further broken up in form of some chunky pieces. Granola cereals are always sold in natural form (without any further addition of antioxidants and fortification). Efforts are made to make the granola cereals fat-free.
Granola Cereals

Conclusion:

Research and development of extrusion technology have made many of the things quite easier in today’s mark and it will continue to do so further. RTE cereals are quite susceptible to spoilage, and they need to be packaged and stored smartly to maintain the required flavor, crispy texture, and shelf life of the product. Typical packaging materials involved in the case of RTE cereals are BOPP, LDPE, PET, aluminium foil, etc. Tubular drag conveyors are preferred for industrial operation in conveying systems due to ease of operation and flexibility. Machines in RTE cereal processing are mostly made from stainless steel. Various testing operations are involved before packaging to ensure all the nutritional claims on the label.

Breakfast is the first meal of the day for all the people. In today’s era of continuous hustle-bustle, it becomes important to manage our time and to look after our health. Consumption of RTE cereals becomes an important thing considering various such perspectives. It is important to start the day with a nutritious meal and ready-to-eat cereals are the best-suited option as it overcomes the problem of other vast processing at home. The use of additives is quite common in RTE cereals as it becomes important to take care of wholesome nutrition requirements and incorporate the factors related to spoilage, flavor, and color development, and obtain certain textures and shapes before consumption.

Marketing plays an important role as most of the RTE cereals come in various shapes and flavors that make a kind of thing fascinating for children. Primary advertising methods like humor and promotional appeal succeeds in attracting consumers of all stages. The company that succeeds in advertising media is also the one that leads in business and market shares. Breakfast cereal processing is a highly penetrated business in matured markets as it has generated revenue with a total of around $62.7 billion last year.

RTE Cereal Processing
RTE Cereal Processing

The rise of twin-screw extrusion cooking with precise control over different parameters through automation led to many process simplifications today. Newer product development category will be in huge demand for the upcoming future to make RTE cereals as a part of complete nutrition and a complete meal to be consumed at any time during the day.

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