Extrusion

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Extrusion

• Some examples

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Licorice Extrusion
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Ingredients

• Wheat flour
• Sugar (sucrose, corn syrup)
• Gelatin or starches
• Emulsifiers
• Water
• Color and flavor (licorice black juice,
  aniseseed, caramel, berry flavors)

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Dry ingredients flour, sugar
Sugar syrup Licorice syrup
Metering
MIXING COOKING
Minor Ingredients
COOLING TUNNEL
CUTTER SHAPER
EXTRUSION
Conveyor
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Cooking begins Sugar dissolves Starch granules
hydrated gelatinized
Pressure increased just prior to die to
force product through die
Water vented cooled Colors flavors
added Mixed with candy
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Direct Expanded Snack Foods
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Ingredients

• Cereal grains such as corn, wheat, rice or oats
• Water
• Oil
• Flavor coatings

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• Usually produced at high shear
• Temperatures greater than 100C
• Pressures kept high-water remains liquid at T gt
  100C
• 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

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Breakfast Cereals
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Breakfast Cereals

• Instant
• Direct expanded
• Flaked
• Gun puffed
• Oven puffed
• Shredded

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In general mixing, cooking, forming,
texturizing, drying
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• Materials may be precooked
• Boiling water cooker
• Steam cooker
• Adiabatic extrusion-high shear in extruder
  creates heat
• Extrusion- adiabatic plus added heat

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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
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Cooked grain particles fed to flaking rolls.
Particles must deform without fracture.
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Doughy particles pass through small gaps
between Rollers. Rough surfaces help pull
particles through nip, are compressed and flow
out from the rollers
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Slightly dry product helps form irregularities.
On further baking these help form crisp
texturized product
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• 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

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Dry to 10-24 moisture (tempering) To overflow
bins On to flaking rolls Further drying/toasting
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Extrusion Puffed Cereals

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

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Product puffs as moisture flashes off
Superheated dough
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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
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Treated with steam cooking to appropriate
moisture level
Cooled and dried to 9-11 moisture
Flaking roller with wide gap
Uniform pieces
Fluidized bed dryer T 340C
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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.
9-11 moisture
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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
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Baking or oven puffing
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Gun puffing
Product 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
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Shredded Cereals
Extruder cooked and formed pellets fed to
shredding machinery One roller embossed with
grooves to cause shredding
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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
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To oven
Strands are collected in layers on a conveyor.
Crimping rolls form biscuit edges
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During baking, the outer layers shrink more
causing the biscuit to puff