Extrusion

Some examples

Licorice Extrusion

Ingredients Wheat flour Sugar (sucrose, corn syrup) Gelatin or starches Emulsifiers Water Color and flavor (licorice black juice,

aniseseed, caramel, berry flavors)

Dry ingredientsflour, sugar Sugar syrup

Licorice syrup

MIXINGCOOKING

Metering

EXTRUSION

Minor Ingredients

Conveyor

COOLING TUNNEL CUTTERSHAPER

Cooking beginsSugar dissolvesStarch granules hydrated& gelatinized Water vented & cooled

Colors & flavors addedMixed with candy

Pressure increased just prior to die to forceproduct through die

Direct Expanded Snack Foods

Ingredients Cereal grains such as corn, wheat, rice

or oats Water Oil Flavor coatings

Usually produced at high shear Temperatures greater than 100°C Pressures kept high-water remains liquid at T > 100°C On exit, moisture flashes from product causing

expansion Loss of water and cooling cause structure to set Additional drying needed to reduce moisture from

15% to 2-3% Coated with oil and lfavorings

Breakfast Cereals

Breakfast Cereals Instant Direct expanded Flaked Gun puffed Oven puffed Shredded

http://www.ktron.com

In general: mixing, cooking, forming, texturizing, drying

Materials may be precooked Boiling water cooker Steam cooker

Adiabatic extrusion-high shear in extruder creates heat

Extrusion- adiabatic plus added heat

Flaked cereals

Corn grits and/or wheat are mixed with salt, sugar, malt etc and cooked with steam to form gelatinized mass.

Mass broken up into pieces

Cooked grain particles fed to flaking rolls. Particles must deform without fracture.

Doughy particles pass through small gaps betweenRollers. Rough surfaces help pull particles through nip, are compressed and flow out from the rollers

Slightly dry product helps form irregularities. On further baking these help form crisp texturized product

In later improvements, cooking and pieces are formed in a screw extruder

Relatively low shear is used and modest heating. Starch is gelatinized but excess shear damages starch.

Die resistance is low to maintain relatively dense strands

Die-face cutting may be unsatisfactory because pieces are too uniform

Dry to 10-24% moisture

(tempering)

To overflow bins

On to flaking rolls

Further drying/toasting

Extrusion Puffed Cereals Superheated gelatinized cereal

emerges from extruder die Moisture flashes and causes puffing Die determines shape Typically high-shear extruders

Superheateddough

Product puffs as moisture flashes off

Oven puffing

Used for crispy rice products

Cooked cereal piece exposed to very high temperatures

Product expands into a cellular structure

With proper moisture in the grain, this is similar to popcorn

Need: moisture inside the kernel, starch inside the kernel and a hard shell to contain the pressure

Treated with steam cookingto appropriate moisture level

Cooled and dried to 9-11% moisture

Flaking roller with wide gap

Uniform pieces

Fluidized bed dryerT ~ 340°C

9-11% moisture

High heat raises pressure in grain. Hard shell keeps water from rapidly escaping. Water is superheated.

At some point the pressure is sufficient to rupture the kernel. Water rushes out and puffs the product.

Extruded pieces may also be oven puffed

Often extruded ribbon embossed with waffle grid, fluting, etc to create interesting texture, then cut and oven puffed

Baking or oven puffing

Gun puffingProduct heated under pressure in closed vessel

Vessel suddenly opened

Decompression causes moisture to flash

Used in puffed wheat. Product looks more like original grain than with direct oven puffing

Shredded Cereals

Extruder cooked and formed pellets fed to shredding machinery

One roller embossed with grooves to cause shredding

Product fed into rollers. Pieces are extruded through serrations in one roller, are crushed and merged into a continuous steam

Strands are collected on a conveyor

Strands are collected in layers on a conveyor. Crimping rolls form biscuit edges

To oven

During baking, the outer layers shrink more causing the biscuit to puff