Extrusion, Cereal

Extrusion Process

Extrusion Process

Processes

An important process being used with cereal products is the extrusion process.The extrusion of materials is nothing new. Historically, the confectionery and the baking industry, particularly cake frosting, has used extrusion cooking. These are first generation extrusion products. Currently, extrusion has expanded from the use of cold candies and frostings, into many cooked products. There are several types of extruded and coextruded products available on the market place. One of the keys to the wide variety of is the die through which the material is pumped.
There has been a lot of work done in this area. The use of extrusion for preparation of pasta products has increased its use and variety. A considerable amount of work has been done on how it affects the final product. A number of the factors are extrusion formula, extrusion temperature, screw speed, screw design and moisture content of the feed product.
Because of the formulation, the products can be different. There is possible the use of many different types of grains and seeds such as cornmeal, corn flour, and potato flour. From this a crisp product, a light product can be gotten. With these many ingredients, a second-generation snack food can be expanded and made in many forms. These second-generation snacks are expanded directly from the extruder diet and proceeded through a dryer to obtain an appropriate moisture content.
A third-generation product is produced from a multiple-ingredient formulations and is generally based on a starch, such as corn or potato. It usually requires an extruder for cooking and expansion as well as an extruder which redensifies and cools the extrusion. It still goes through a dryer.
Co-extrusion permits the development of products which produce an outer tube of one material and filling it with another in one operation. This is a unique controllable process. From this, snacks with a crisp outer layer and a soft inner core can be made.
Not only are pastas extruded. but there are a whole series of well-flavored snack foods and crackers. An investigation of extruded products would indicate that there are differences in the developed continuous phase from that of conventional cooked products. In extruded products the continuous phase is the starch granules. In the conventional product the continuous is protein with starch immersed throughout it. In extrusion cooking gas cells are formed by spontaneous nucleation of steam. The air cells in conventional products is the source of the air cells. These differences cause extruded products to generally be hard, brittle and friables. Breads, cakes, biscuits are generally soft, viscoelastic gels.
Cereals have been processed by extrusion since the mid 1950s. It is impossible to keep up with the processes of this rapidly increasing area of food production. Manufacturers such as Wenger are sources of the latest assistance and help. Extrusion of products have been done with products from pastas, cereals, meat, to even vegetable and fruit purees. Basically the process consists of pushing a formula, i.e. product, through with a screw extruder, and out a opening of various sizes..

Screw Extruders

Single Screw Extruder with permission
from Wenger
Twin Screw Extruder
Twin Screw Extruder used with permission
from Wenger
The screw portion of the extruder is critical for the type of product and its characteristic. The extruders will vary in their geometry of the screw itself, the turn rates, the heating rates, and the die sizes.

HTST Extrusion
HTST is a viscous drag screw pump which is operated at temperatures and pumping rates high enough to cook a product and yet extrude out the product. There are three zones of this type of extrusion. The feed zone where it is heated and moisture adjusted is simply to bring the formula into action [mixing, compressing] without cooking it. There is a cooking zone where the product is stirred, cooked and compressed into the product desired. This product is generally somewhat plastic like material. The final, or third section of the process is the die or extrusion cap. With the temperature being high in the product this is where, upon extrusion, the moisture will vaporize and expand the product. There is a loss of moisture and cooling.

Oregon State