Module 2. Cereal processing

Lesson 9

BREAKFAST CEREALS: CLASSIFICATION AND TECHNOLOGIES

9.1 Introduction

In this century, cereal grains have found a significant use as breakfast foods. Breakfast cereal technology has evolved from the simple procedure of milling grains for cereal products that require cooking to the manufacturing of highly sophisticated ready-to-eat products that are convenient and quickly prepared. Breakfast cereals are generally eaten cold and mixed with milk as opposed to hot cereals like oatmeal, grits, etc.

9.2 Definition and Classification of Breakfast Cereals

9.2.1 Definition

Breakfast cereals have been defined as “processed grains for human consumption”. One or more of the cereal grains or milled fractions therefore are indeed major constituents of all breakfast cereals, approaching 100% in the case of cereals for cooking. The proportion drops well below this in many ready-to-eat cereals, and to less than 50% in pre-sweetened products. They are made primarily from corn, wheat, oats, or rice and usually with added flavour and fortifying ingredients.

9.2.2 Classification

Ready-to-eat (RTE) cereals are made primarily from corn, wheat, oats or rice usually with added flavour and fortifying ingredients. Breakfast cereals are classified into two major categories: hot cereals and RTE cereals

Hot cereals are made primarily from oats or wheat nevertheless; hot cereals from corn or rice are produced in relatively small quantities. Hot cereals require cooking at home before they are ready for consumption with the addition of either hot water or milk.

The processing of RTE cereals involves first cooking the grains with flavouring material and sweeteners. Sometimes more heat stable nutritional fortifying agents are added before cooking. Most RTE cereals are grouped into eight general categories:

1. Flaked cereals
2. Gun-puffed cereals
3. Extruded gun puffed cereals
4. Shredded whole grains
5. Extruded and other shredded cereals
6. Oven puffed cereals
7. Granola cereals
8. Extruded expanded cereals

9.3 Manufacturing Processes for Breakfast Cereals

The proprietary nature of the breakfast cereal industry limits the information base to patent records and publications by individuals not directly associated with industry. In broad terms, breakfast cereal ingredients may be classified as grains or grain products, sweeteners, flavouring, texturizing ingredients, and micro-ingredients for nutritional fortification and preservation. The processing of ready-to-eat cereals typically involves first cooking the grains with flavouring material and sweeteners, followed by forming operation.  Sometimes the heat stable nutritional fortifying agents are added before cooking. Two cooking methods are employed in the industry -direct steam injection into the grain mass and continuous extrusion cooking.

Various unit operations are involved in the manufacturing of the breakfast cereals such as tempering, cooking, puffing, flaking, shredding, baking and drying, etc. These unit operations yield breakfast cereals with certain forms such as puffed, cracked, flaked, cakes, pellets or definite shapes such as circular, cylindrical, rectangular, nuggets, oval, triangle; and irregular shapes such as chunks.

9.4 Processing Steps

9.4.1 Cooking

Flaked breakfast cereals can be made by cooking whole kernel cereals or legumes by pressure cooking followed by pressing through rollers. Alternatively it can be made by extrusion cooking of flour. Cooking helps in development of desirable flavour and nutritional benefits. It also assists in creation of desirable physical properties necessary for the development of desire texture – primarily by starch gelatinization.

9.4.1.1 Batch cooking

Corn flakes, wheat or bran flakes and shredded wheat are processed in batch pressure cook processes, where steam is injected into the pressure cooker. However, atmospheric cooking with steam injection especially in case of shredded wheat in steam jacketed mixing vessel is also used. Product from the batch pressure cooker forms lumps or individual grits, which are subsequently delumped before the next processing step, which is drying.

9.4.1.2 Extrusion cooking

The starting material for extrusion cooking is dough from which intermediates or half products are anticipated prior to puffing or flaking. Different types of extruders are employed in manufacture of breakfast cereals such as single screw, twin screw or kneading or forming – type extruder.

9.4.2 Tempering

Tempering is a physico-chemical effect that influences the quality of finished product. Tempering follows a drying or cooling step and is the period during which the cooked grain mass or cereal pellets are held to allow the equilibration of moisture within and among the particles. It assist in the development of desired flakability or shredability.   During tempering the retrogradation of starch (firmness of grain due to starch crystallization) allows moisture equilibration.

9.4.3 Puffing

Puffing is a thermal process in which rapid heat transfer takes place in order to phase shift the water to a vapor. Two things are important for grain to puff – the grain must be steeped or cooked, and a large, sudden pressure drop must occur in atmosphere surrounding the grain. Rice and wheat are most widely used cereals for puffing. They are puffed as whole kernel grains.

In gun puffing, high temperatures are attained (600 – 800°F) followed by a pressure drop of 100 – 200 psi. A rotating gun is heated by means of gas burners with very hot flames; the moisture in the grain is converted into steam. When the lid is opened to fire the gun, the internal pressure is released, and the puffed grain is caught in a continuously vented bin.

9.4.4 Flaking

Flaked products are produced by passing tempered grits or pellets through two large counterrotating metal rolls, one of which is adjustable so that the distance between them or roll gap can be set to produce a flake of the desired thickness. These rolls are hollow and are internally cooled by passing water through the interior of the roll. A scraper knife on each roll removes the flakes, which are then conveyed to toasting oven.

9.4.5 Shredding

The grain used in whole kernel form for shredding is primarily wheat. Shredded wheat is made by cooking soft white wheat in an excess of water at atmospheric pressure. The drained wheat is cooled to ambient temperature and contains approximately 50% moisture. The next step is tempering for 24 hours to allow for moisture equilibration and firming of the kernel. Next, the wheat is squeezed between two counterrotating metal shredding rolls – one with a smooth surface, the other grooved. Shredding rolls are water cooled to control the roll surface temperature. The shreds are laid down on a conveyor under the rolls running parallel to the shredding grooves and subsequently conveyed to dryer for drying to a final moisture content of around 3 – 4%.

9.4.6 Baking

Cereal granules or granola cereals are usually produced using a modified bread baking process. A stiff dough is prepared from wheat flour, malted barley flour/rolled oats, salt, yeast and water. Other raw materials such as nut pieces, coconut, honey, malt extract, dried milk, dried fruits, vegetable oil, spices can also be added. The dough is mixed and allowed to ferment for 4 – 5 hours at 80°F and 80% relative humidity (RH). After fermentation the dough is baked at 300 - 425°F until the material is uniformly toasted to a light brown and moisture reduced to about 3%. The dried pieces are ground into small pieces and screened to obtain desired particle size. The final product has a notable crunchy texture.

9.4.7 Drying

Most ready-to-eat breakfast cereals require drying as an intermediate processing step. This drying is the controlled removal of water from the cooked grain and other ingredients to obtain appropriate physical properties for further processing such as flaking, puffing, forming, toasting or packaging. Cereals are dried at various stages of processing. Pellets for flake products have a moisture content of 30 – 33% prior to the drying and are dried down to 16 – 22% moisture. Pellets for gun puffing are dried from 30 – 32% to 10 – 12% moisture. This pre-drying prevents agglomeration of cooked cereals. Multipass dryer design for better control over residence time and humidity are widely used for drying of cereals.

9.5 Additives in Breakfast Cereals

Most breakfast cereal products contain large amounts of cereal grains and have small quantities of additives. Breakfast cereals available in market are manufactured from variety of cereals such as corn, wheat, oats, barley, rice, rye singly or in combination. Although breakfast cereals are usually eaten/mixed with milk, certain breakfast cereals contain milk solids as one of the ingredients. In broad terms, breakfast cereal ingredients may be classified as (1) grain or grain products, (2) sweeteners, (3) other flavouring or texturizing ingredients, (4) minor ingredients for flavour and colour and (5) minor ingredients for nutritional fortification and self-life preservation.

9.6 Additives in Breakfast Cereals

 Some of the additives used in manufacture of breakfast cereals are listed in Table 9.1

Table 9.1 Ingredients found in breakfast cereals (Listed by function, some ingredients serve more than one function, as indicated by parenthetical notes)

Ingredient	Examples
Cereals	Wheat: Defatted wheat germ, Wheat bran, Wheat germ, Wheat gluten (protein source), Whole rolled wheat, Whole wheat, Whole wheat flour
	Corn: Corn flour, Degermed yellow corn meal, Milled yellow corn
	Oats: Oat bran, Oat flour, Rolled oats, Whole rolled oats, Whole oats, Whole oat flour
	Rice: Milled rice, Rice flour
	Barley: Malted barley (sugar source), Whole barley
Sweetening agents	Brown sugar, Brown sugar syrup, Cereal malt syrup, Dextrose, Fructose, High fructose corn syrup, Honey, Invert sugar, Malted barley (cereal), Malt extract, Molasses
Fruits (sugar source)	Strawberries, Apple juice, Dates, Dried apples, Strawberry juice concentrate, Apple juice concentrate, Grape juice concentrate, Raisins
Flavours	Malt flavouring, Salt, Cinnamon, Cinnamon extractives, Cocoa, Artificial flavours, Malic acid, Sodium citrate, Citric acid (stabilizer), Yeast (structural), Sodium bicarbonate (structural), Natural flavours
Structural additives	Gelatin (protein), Corn starch, Modified food starch, Wheat starch, Maltodextrin, Pectin, Sodium alginate, Sodium phosphate (dough conditioner and mineral), Glycerine, Trisodium phosphate, Calcium carbonate (mineral), Baking powder, Tricalcium and dicalcium phospahate, Wheat gluten, Cellulose gels and gums
Fats (Partially hydrogenated oils)	Coconut, Cottonseed, Soybean, Palm, Palm kernel, Groundnut
Dairy products	Dried whey, Calcium caseinate, Non fat dry milk, Whey protein concentrate
Protein sources	Nuts and legumes (flavour, fat), Peanut butter, Soy flour, Almond pieces, Coconut, Hazelnut, Pecan pieces, Walnut pieces
Vitamins	Vitamin A palmitate, Vitamin C, Sodium ascorbate, Ascorbic acid, Vitamin D, Vitamin E, DL – alpha tocopherol acetate, B vitamins, Niacin, Niacinamide, Folic acid, Thiamine mononitrate, Thiamine hydrochloride(B 1), Pyridoxine hydrochloride (B 6), Vitamin B 12
Minerals	Reduced iron, Tricalcium and dicalcium phospahate, Calcium pantothenate, Calcium carbonate (structural), Sodium phosphate (structural), Zinc oxide
Preservatives and stabilizers	Butylated hydroxyanisole (BHA) in packaging (antioxidant), Sulfur dioxide (in fruit), Citric acid (flavour), Mono- and di- glycerides, Soy lecithin
Colours	Artificial colour: Red 40, Yellow 5, Yellow 6, Blue 1 Natural colour: Caramel colour, Beet powder, Annatto extract

9.7 Functions of Additives

Within each listed items in Table 9.1 there are large number of subcategories. E.g. sugar includes sucrose, honey, glucose, invert sugar, corn syrup solids, etc. Sugar imparts sweetness to the product and it is sometimes used as coating material.

· Buffering salts such as mono-, di- or trisodium phosphates are added to adjust the pH of the cooked dough for browning and gelatinization.

· Salt is commonly added either to base mix or added to the surface in snacks for flavouring purpose.

· Emulsifiers like distilled mono- glycerides and distilled di-glycerides are added to reduce the stickiness of the product.

· Components like minerals and vitamins are also incorporated into the cereals as per Recommended Dietary Allowances (RDA) for a nutritional claim to be made.

· Fruits, dried fruits, milk products are also added to further improve the nutritional value as well as sensory characteristics of the breakfast cereals.

· Modified starches, specialty flours and stabilizers are added primarily as texturizing agent.

· Addition of oil, leavening agents and/or emulsifiers affects and contributes to shape, texture and eating quality of ready-to-eat cereals.

· Antioxidants either natural or synthetic are incorporated into the cereals to improve the shelf-life of the ready-to-eat cereals.

· Various flavourings (natural, nature-identical, synthetic) and colouring (natural, synthetic) are extensively used to improve the sensory and aesthetic quality of the ready-to-eat cereals.