Pasta extrusion process

Extruded food products such as pasta, snacks and ready to eat cereals differ from bakery products in the way their texture is formed.

In order to give the pasta its desired shape, the dough in its plastic state must be forced through an appropriate die relatively high pressure.

In the case of continuous extrusion presses, this pressure is generated by a screw. The ingredient are fed into a continuous high capacity extruder that is equipped with a variety of dies to produce having different shapes and appearance.

The shape of the holes in the die governs the shape of the pasta. For spaghetti, the die has round holes; for macaroni wheels, the die pushes the pasta. Leaving a large hole in the middle and gaps left by the spokes. 

When the extruded pasta reaches the right length, it is cut with sharp blades that rotate beneath the die.

Pasta extruder barrel are equipped with a water cooling jacket to dissipate the heat generated during the extrusion process and to help maintain a constant extrusion temperature around 35-50 °C to avoid gluten damage.

Most pasta shapes can be classified into two groups: long goods and short goods. The most familiar type of long goods is spaghetti which may have diameter ranging from 1.5 to 2.5 mm. Hollow extruded goods commonly referred to as macaroni, come in various lengths an forms.
Pasta extrusion process

Pasta Technology - Die construction

Pasta Technology - Die construction
The basic operation in the manufacture of any kind of pasta is extrusion.

The dough is prepared by the mixer, kneaded by the auger from the mixer to the die chamber, and the force through a die under high pressure.

Dies perform the function of forming the dough into characteristic, familiar shapes.

They are made in both circular and rectangular form, depending on whether they are to be used in oppresses for producing short goods or in an automatic spreader for long goods.

Dies are often made of bronze but stainless steel and other alloys have also been employed.

Combinations of material can be used, as when s stainless steel frame is fitted with brass inserts which can be removed and replaced.

The simplest form of pasta is the familiar spaghetti which is a solid round strand of dough.

On the inlet side of the die the hole is about 0.19 inch in diameter, although slightly different diameters may be employed by different manufacturers.

As the channel proceeds toward the exit orifice, it tapers down to about the diameter of the spaghetti and this diameter is maintained for short distance called the gauging thickness.

Tubular forms, such as macaroni, require a pin in the center of the die. The pin is anchored by two or more wings or extensions near inlet end.

The stream of dough is, of course separated by these extensions, but quickly merges together after it passes them and continues along the channel.

Curved elbow macaroni is formed by drilling one side of the die hole deeper than the other so that the dough will flow faster on that side – there is less friction because the channel is wider for part of its course.

In large elbow macaroni with thick pins, a notch can be cut into the pin to cause the dough to flow faster. Products with wavy edges can be made by allowing the dough to flow more rapidly at the wavy edge.

The extrusion rate through a die hole in a bronze die is normally about one inch per second.

Extrusion rates can be increased and the product made smoother and yellower by putting Teflon inserts into die so that the final extrusion surface is made of this very smooth and low friction material.

Teflon does have come into wide use in marketing regions where products are packaged in transparent film and must therefore have optimum visual quality. Bronze dies are used in area where the pasta is packaged in opaque containers such as cardboard boxes.

It is generally believed that bronze dies yield pasta that cooks in a more satisfactory manner.

Water penetrates more slowly into the Teflon-extruded product and there is a tendency for the surface to become soft before the interior has been thoroughly cooked.
Pasta Technology - Die construction

Pasta Processed from Sprout Damaged Grain

Pasta Processed from Sprout Damaged Grain
Germination (sprouting) of grain before harvesting can be a problem when rain and cool weather prevent or slow down normal harvesting operations.

Pasta manufacturers are particularly sensitive to using semolina milled from sprouted durum wheat in their pasta processing operations since it can affect end product quality.

Several studies have been conducted of the problems of sprouting terms of pasta quality.

Some general conclusions from those studies indicate that test weight, kernel distribution, protein content, milling performance, pasta color, and cooking quality were not adversely affected by increasing sprout damage.

The only major adverse effect appeared to be higher semolina speck counts and spaghetti shelf stability.

It was noted that sprout damage levels of 4.0% or higher (Falling Numbers of 120 or less) resulted in pasta products having high potential for checking and cracking in storage.

Commercial manufacturers of spaghetti are concerned not only with the problems mentioned above but also with the tendency of spaghetti processed from sprout-damage grain to stretch and fall off the rods during drying.

Because of such concerns a number of US pasta manufacturers will not process pasta form semolina with Falling Numbers less than 300.

Result indicate that pasta can be processed utilizing semolina with Falling Numbers of 250 without any apparent problems, so commercial manufacturer’s use of semolina with values of 350 and higher provided a large margin of safety.
Pasta Processed from Sprout Damaged Grain

Pasta Processing –Dies

Pasta Processing –Dies
In the ultimate analysis, it is the die which establishes the distinctive character of the product. Not only the appearance, but the texture of the cooked food and the way it interacts with the sauces and flings are functions of the shape and dimensions of the pasta.

Die makers have demonstrated an enormous amount of ingenuity in shaping the orifices, inserts and channels so as to make hundreds, of not thousands of different products by this basically very simple method.

Some problems do exist. The dies and inserts must be machined to very close tolerances of the shape and thicknesses of products emerging from every orifice are to be uniform.

If the die wears unevenly, and most do, the characteristic shape will subtly alter through a period of weeks or months of use.

Small pieces of grit or hard dough hanging up in a die channel will completely alter the shape of the product emerging from that orifice.
Pasta Processing –Dies