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Extruders not just for snack food.
Extruders not just for snack foods
Recent extruder applications provide improved product quality and cost savings.
by Franklin Kramer, Technology Analyst
May 01, 2000
plants of tomorrow - extruders - may 2000
Extruders, a unit operation import from the plastic industry, have been very important in food processing. Their use continues to spread, and in recent years shows advantages for many new areas of food production. Uses have expanded to include bakery, confectionery and chewing gum processing.
There are basic reasons for this:
* Flexibility -- The same machine can produce a variety of products with only minor adjustments.
* Continuous -- It fits the rest of a continuous line and readily adapts to computer process control.
* Short residence time -- Materials usually remain in the extruder for very few minutes.
* Wiped surface (on some types) -- This is good for handling viscous/sticky foods.
* Availability of different extruder types -- Different screw and die configurations provide a variety of possible applications -- mixing, cooking, forming or a combination of these actions.
* Testing facilities -- Extruder vendors offer test runs on their equipment at reasonable rates.
* Competing extruder vendors -- provide more opportunities for choice at least cost.
Types of extruders and how they work
Basic extruder types:
Single screw--Vendors: Wenger, SPR; Features: Mixing, pressure, and heating, forming
Twin screw--Vendors: KWP, APV & Wenger; Features: Adds wiped surface and flexible screw configuration
Single reciprocating screw--Vendors: BUSS; Features: Same as twin screw plus low pressure and temperature
Single screw extruders were the first types to be used in the food industry and continue to have a wide use in products like pasta, cereals and pet foods. The twin, co-rotating screw extruder began being used for food products such as snack foods in the 1970s and began to replace single screw extruders in many applications. The twin screw offered advantages because of the wiped surface and screw configuration flexibility features. These features allow for a more varied product use of twin screw over the single screw. The single screw, with a fixed screw flight design, is best suited for dedicated use and is not as well-suited for processing with viscous or sticky materials.
A big attraction for the single screw is its lower investment cost. The single reciprocating screw is a unique type. It has many of the twin screw characteristics but is of special value for mixing with only slight temperature rise.
Wenger Manufacturing, Sabetha, Kan., and Scientific Process Research, Somerset, N.J., make single screw extruders. Wenger has focused on extruders for the food industry, providing single as well as twin-screw equipment. SPR designs and fabricates specialty type extruders and dies from basic material properties using in-house-developed computer programs. Besides using its own designs, the SPR sophisticated machine shop fabricates the equipment directly from the design computer files.
Krupp Werner Pfleiderer, Ramsey, N.J., makes mixing equipment for the chemical, plastic and food industries. In the mid-'70s it popularized the use of twin screw extruders in the U.S. food industry. KWP demonstrated how the twin screw flexibility justified the added investment. It was particularly attractive because with various arrangements of the screw elements, it can be quickly set up for use with different products. Further, the twin screw extruder can be used continuously while metering five, 10 or more ingredients simultaneously into designated sections of the extruder. Also, pressure and temperature profiles can be beneficially adjusted by rearranging the screw elements, varying the RPM and/or adjusting heating and cooling elements located in the extruder covers.
BUSS, a Swiss company, makes single screw extruders with the wiped surface capability of a twin screw that provides excellent mixing without temperature and pressure buildup. The wiping is accomplished with a reciprocating motion of the screw shaft and by precise positioned screwblades and fixed pin placement. With each back and forth shaft movement, the fixed pins, mounted in the stationary cover, clean off each screw blade. The BUSS also comes with screw element flexibility and ease of adding ingredients at any point.
New extruder applications
Producing gum base and chewing gum products has long been conducted by individual ingredient weighing and with manually operated batch mixers as the principal unit operation. The product, such as bubble gum or stick gum, was defined by the ingredients used, mixer parameters and the downstream forming and cutting equipment.
Today, KWP and BUSS have extruders in commercial operation that prepare gum base and chewing gum continuously. The gum base ingredients are continuously mixed and then formed into pellets. The pellets, along with the other ingredients, are continuously metered into an extruder to prepare the "paste" for downstream forming and packaging. There are patents that describe doing both gum base and chewing gum produced in the same extruder (U.S. Pat. 5543160); also, patents that describe producing thin stick gum slabs directly from the extruder and an attached "coat hanger" die (U.S. Pat.4555407). Without a need for a complex set of calendar rolls, the slabs are ready for packaging.
Commercial bakery processes have become more and more automated, continuous and computer controlled. This is particularly advantageous in producing heavy dough products like danish pastry, breads/rolls and croissants.
The one step that has remained a batch operation is the initial dough mixing. Traditional sigma blade mixers are used albeit often with computer control. However, even automated SB mixers utilize valuable space, are difficult to clean and require operator attention. Extruders have operated in Europe where bread, pie and danish dough are prepared in BUSS's continuous mixer extruder with all ingredients automatically metered in; a homogeneous dough rope is formed at low temperatures and with good quality.
Producing dry breakfast foods like corn flakes requires rather elaborate processes. The front end of the process has been greatly simplified, substituting twin screw extruders for the group of batch pressure cookers traditionally used. The extruders produce dry pellets that can be stored and shipped before final processing through equipment like flaking rolls, toasters and coating drums. Besides the usual advantages as stated for the bakery products, extruders for breakfast foods production have advantages in adding manufacturing flexibility as well as plant location options.
APV Americas-Baker, Grand Rapids, Mich., which specializes in breakfast food equipment, has the extruder technology and the machinery for this improved manufacturing process.
The food processing industry continues in its quest for consistently high-quality products with the same or reduced operating costs. The opportunity today is to take advantage of the ever-increasing availability of new technologies. The use of extruders illustrates this point.
Frank Kramer is the president of Freemark Co. and a consultant with Stratecon International Consultants. Reach him by fax at (941) 923-1609.
