Noodle Processing Although noodle formulations, sizes, and shapes vary widely, the process of forming noodle bundles from different types of pasta is remarkably constant. It typically involves mixing the noodles, formation of a noodle band, laminating two noodle bands, reducing the thickness of the noodle band by calendering, and forming the noodle band by passing it through a pair of cutting rolls. After cutting, there is a great deal of flexibility for further processing and packaging. Noodles can be packaged and sold as raw noodles, or they can be dried, steamed, fried, boiled, frozen, or a combination of these processes to produce different types of noodles.1 Basic processing: from flour to raw noodles 1.1. mixing

Mixing is the first step in pasta processing. Most of the ingredients are pre-dissolved in water and stored in jars. Weigh the wheat flour and place it in the pasta machine with the appropriate amount of water. In pasta processing, the main purpose of mixing is to distribute the ingredients evenly and hydrate the flour particles. Low-absorbent doughs have little or no gluten formation during the mixing stage. However, in high water absorption doughs (>35%) and long mixing times (>15 min), the degree of gluten formation may be significant. The dough should be kneaded so that its gluten proteins are hydrated as much as possible, but not to such an extent that the rolls stick during calendering due to tackiness. This will maximize the formation of a continuous gluten matrix with embedded starch granules during calendering.

There are two types of pasta machines commonly used in the pasta industry: horizontal pasta machines and vertical pasta machines. They both provide good mixing and some kneading during the mixing process. Both types of mixers usually mix at medium speed (70-100 rpm) for 10-20 min.

Vertical mixers are better suited for large-scale automated continuous pasta production. The mixing blades of most vertical mixers have a large surface area. In the early stages of mixing, they are very effective in distributing water evenly throughout the flour. Once the flour particles are fully hydrated, vertical mixers can also provide a degree of kneading action.

Horizontal mixers can have either a single or double shaft. The latter has proven to be more effective in dough mixing. Two shafts with special blades rotate in opposite directions during the mixing process. The blades attached to the two shafts are interconnected so that the wadding moves vertically and horizontally in opposite directions at the same time. These mixing behaviors help in uniform mixing and promote gluten formation by the knocking action of the blades.

Several new types of pasta machines have been developed for the pasta industry: continuous high-speed pasta machines; low-speed super pasta machines and vacuum pasta machines. Continuous high-speed mixers can mix flour and water in a matter of seconds. In the mixer, the water mixture is sprayed at 1500 rpm into the flying fine flour particles. The high speed of the mixer creates a large surface area for the water and flour, allowing the flour particles to hydrate evenly and instantly. The Low Speed Super Mixer was developed for mixing highly absorbent doughs. It is designed to mimic hand mixing and operates at very low speeds (<10 rpm) to avoid damaging the gluten structure. The combination of high absorbency, long mixing times and a special kneading action produces a dough with a well-developed gluten structure. Vacuum kneading machines are widely used in modern noodle mills. Mixing under vacuum allows additional water to be added to the flour without causing processing problems. This allows the flour particles to be fully hydrated and the gluten network to be efficiently formed during the mixing and subsequent calendering process.

In addition to the mechanics of the mixing machine, the mixing is also influenced by the quality of the flour, the amount of water added, the presence/absence and quantity of certain ingredients (in particular salts and alkaline salts), and the temperature and humidity of the processing environment. Flours with a high protein content hydrate relatively quickly and tend to form large flakes, thus requiring less mixing. Once starch granules are damaged during milling, their hydration capacity increases significantly and competes with the gluten component of the flour for the limited water in the dough. Flours with high starch damage require higher water absorption and longer mixing times. For most noodles, the amount of water added during the mixing process should be maximized as long as good dough processing properties are assured. As the amount of water added increases, the development of surface tackiness of the dough tape requires limiting the water absorption of the dough. The dough strengthening and shrinking effects of salt and alkaline salts permit the addition of more water without causing processing problems. Salt also promotes hydration of flour particles during the dough mixing process. Mixing at low temperatures (<20°C) may slow down the hydration of the flour and the formation of gluten. It is also not advisable to mix dough at high temperatures (>35°C) as this increases enzyme activity and may damage gluten. The optimum mixing temperature for most doughs is 25-30°C. The dough is usually cooked after mixing.

After mixing, the dough is usually cooked. This step allows the flakes to cook for a period of time to accelerate further water incorporation of the flour particles and redistribution of water in the dough system. Maturing also improves processing properties and promotes the formation of gluten during calendering, which is achieved by relaxation of the gluten structure already formed during the kneading process. The maturing facility is typically located between the kneading machine and the first pair of calendering rolls. Ripening is carried out by summing the dough at a very low speed (5-8 rpm) for 10-20 min. The dough mixing avoids the formation of large flakes during the maturing period and can also be used for the supply of the calender rolls in a continuous process.1.2. Calendering

Although the flour particles are fully hydrated after mixing and maturing, the development of the gluten network is far from complete and is localized without continuity. It is during calendering that the continuous gluten network is formed. The development of a homogeneous gluten network with a good balance of elasticity and ductility is essential to ensure good processing properties and optimum eating quality of the finished product. Under compression, neighboring endosperm particles are fused together so that the protein matrix within one endosperm particle is continuous with that of neighboring particles. The purpose of the calendering process is to obtain a smooth dough strip with the desired thickness, as well as a continuous and homogeneous gluten network in the strip.

The flakes are transferred to a hopper and passed through one or two opposite rollers to form a continuous strip. The freshly pressed bands usually have a rough surface and an uneven texture. One strip is usually folded or two strips are laminated before the next pass. After the second pass, the laminated tapes are usually cooked for as little as a few minutes or as long as several hours. Tapes can be aged by slow passage on a serrated conveyor in an automated plant. Cooking can also be accomplished by storing the tape wrapped around wooden or plastic spools.

Aging loosens the gluten structure. As it cooks, the gluten softens and becomes more malleable. This stage of maturation facilitates subsequent sheet reduction and allows for the development of a more homogeneous protein matrix with fewer pores.

After maturation, the thickness of the composite tape is progressively reduced by passing the composite tape through a series of nip rollers, the gap between these nip rollers being progressively reduced. The number of passes through the rollers varies, but is usually between three and five. The thickness of the final strip depends on the type of pasta to be produced. The gluten matrix in machine calendered dough is aligned in the direction of calendering. This is in contrast to handmade dough, in which the gluten structure unfolds in all directions. The superior texture of handmade pasta depends to a large extent on the degree and manner of gluten formation. Multi-roll and wave roll calendering technology was developed to simulate the hand movements that create the gluten structure characteristic of handmade pasta. In modern noodle factories, the application of this technology combined with high water absorption significantly improves the eating quality of the finished product.

In order to produce pasta with optimum eating quality, it is necessary to obtain a homogeneous and well-developed gluten network at the calendering stage. In addition to flour quality and pasting, the calendering process has a significant impact on the formation of the gluten matrix in the dough strips. The main factors are the undercutting rate, the number of passes and the size, speed, temperature and position of the calendering rollers. The first pair of calendering rolls are slow moving, large in diameter and horizontally aligned to facilitate the feeding of the flakes. Because of the need for high pressure to press the two facebands together, the rolls for the composite passes are usually larger in diameter and are arranged at an angle (mostly 45°). The next reduction process is the formation of smooth face bands with a uniform gluten matrix. The thickness of the strip should be gradually reduced so as not to damage the surface and gluten structure. This is controlled by setting the gap between a series of smoothing rollers. The thickness of the strip behind the composite should not be reduced by more than 40% and the rate of reduction decreases with each successive reduction. The final thickness reduction before cutting should not exceed 10%. With each successive pass, the roll diameter should gradually decrease, thus compressing the distance and reducing the pressure. After each pass, the linear speed of the nip roll must increase as the roll diameter decreases and the length of the strip increases. However, calendering at very high speeds may overstretch the face band without sufficient compression. The speed of each pair of calendering rolls is controlled according to the linear speed of the last pair of rolls and is usually limited to 28 m/min. Since temperature has a significant effect on the physical properties of gluten, it is important to control the temperature of the calendering rolls in order to maintain good tape flow and proper gluten formation during calendering.

1.3. Cutting Once the strip has been reduced to the desired thickness, the strip is cut into noodles in the calendering direction. The width and shape of the noodles are determined by the cutting rollers. The cutting device consists of a pair of grooved rolls with the same groove width. The slots on each roll are offset from each other to permit cutting. The two cutting rolls are arranged horizontally, with the rear side rotating clockwise and the front side rotating counterclockwise at the same speed. A cutting force is generated between two adjacent sharp edges of the two cutting rolls. A comb is located underneath each cutting roller to prevent the pasta from sticking to the rollers. The cross-sectional shape of the pasta depends on the grooves of the grooves, the width of the grooves and the thickness of the pasta band. The usual shapes are rectangular, square and round. There are two systems of specifying pasta knives: metric and imperial. The width of the pasta is equal to 30 mm divided by the number of cutting rolls assigned to the metric units and 25.4 mm divided by the number of knives in imperial units. The noodles are finally cut to the right length by a sizing machine. In the case of instant noodles, the noodles are continuously fed into a moving net conveyor that moves slower than the cutting rolls above it. The difference in speed between the noodle feed and the net movement causes the noodles to produce a distinctive wave. After steam cooking, the shreds are cut into serving sizes and then deep-fried or hot-air dried.2. Secondary Processing - From Fresh Noodles to Finished Product 2.1. Drying

The shelf life of noodles can be significantly extended if microbiological and biochemical stability is ensured. The most effective way to achieve this is to dry the pasta to a moisture content at which microorganisms cannot grow. Moisture can be removed from the noodles by air drying, deep frying or vacuum drying. Frying is an important process in the production of steamed and fried instant noodles, and each will be described below. Vacuum drying is a relatively new technology with very limited application in the noodle industry. Frozen noodles can be vacuum dried to produce a quality product. Based on the maximum drying temperature used in the noodle drying process, air drying can be further categorized into hot air drying (>70°C) and non-hot air drying (<50°C). Non-hot air drying is used in the production of ordinary hanging noodles, while hot air drying is mainly used in the production of steamed, hot air-dried instant noodles.

Fresh noodles with a length of 2-4 m are hung on rods in a drying chamber where the temperature, relative humidity is regulated and ventilated or in a drying tunnel where the rods pass through sections of different controlled environments. Moisture is removed from the surface of the noodles by air. The driving force for dehumidification is the difference between the partial pressure of water vapor on the surface of the pasta and the partial pressure of water vapor in the air. The characteristics of the pasta, temperature, relative humidity and air flow rate are all important factors affecting the drying of pasta. During the drying process, the moisture on the surface of the pasta becomes water vapor and is carried away by the surrounding air. This creates a moisture content gradient within the pasta and the moisture will diffuse as it moves from the center down the moisture gradient to the surface of the pasta. As the rate of evaporation slows, the drying rate is limited primarily by the diffusion of water within the pasta strip. Due to its hygroscopic nature, salt has a significant effect on the rate of moisture diffusion during drying. Noodles with a high salt content dry more slowly than those with a low salt content.

The quality of the pasta must be maintained during the drying process. Improper drying may disrupt the structure of the pasta, resulting in excessive elongation, cracking, warping and splitting. These conditions can lead to problems in handling and packaging. In addition, cooking quality and texture may be severely affected. If an attempt is made to dry too quickly, a large moisture difference exists between the surface and core of the pasta. As the pasta shrinks while losing moisture, the dry surface will try to shrink onto the moist core. The surface of the noodle will be under tension while the core will be under pressure. The pasta will release these stresses by permanently deforming. A proper pasta drying process usually involves multiple stages to minimize undesirable pasta structural changes. A three-stage drying process, including pre-drying, main drying and cooling, is a very common practice.

The first stage, which accounts for 15% of the total drying time, is the most important. In this stage, low temperature (15-25°C) and dry air are used to reduce the moisture content of the noodles from 32% to 38% to less than 28%. Its main function is to dry the surface of the noodles immediately after cutting to prevent the noodles from sticking together and to avoid excessive elongation of the noodles. The pre-drying stage is followed by the first drying stage at fairly high humidity and temperature (75-85% RH, 30-40°C). Internal moisture diffuses to the surface and internal moisture diffusion is balanced with surface moisture evaporation. In the second drying stage, higher temperatures and drier air (40-50°C, 55-60% RH) are used to remove moisture from the noodles. In the final stage, the product is gradually cooled and further dried. The main concern here is the gradual reduction of temperature to avoid internal stress in the noodles.

Health concerns about fats in fried noodles have hindered the production of both steamed and hot air instant noodles. Steamed noodles are dried with hot air rather than fried to a moisture content of less than 12%. Drying is done using hot air at 70-80°C for 30-45 min. The main factors affecting the drying process are temperature, humidity, air pressure, as well as noodle size, moisture content, and bulk density. 2.2. Steaming

Steaming is widely used in noodle processing. As long as the temperature of the steam is high enough, starch dextrination and protein denaturation will occur in wet raw noodles during steaming. The degree of cooking depends on the original moisture content of the noodles, the amount of steam, pressure and temperature, and the duration of steaming. During high-moisture steaming, noodles are sprayed with hot water to accelerate starch pasting, followed by soaking, or washed with cold water after steaming to stop the cooking process. After washing away the soluble starch from the surface of the noodles, the noodles were drained and coated with cooking oil.

To produce high quality steamed noodles, raw noodles must be made from a highly absorbent dough and it is important to use saturated, high-temperature steam during the steaming process. The degree of doneness during steaming is critical. Unsteamed noodles will have a hard core and will be difficult to fry before serving. Over-steamed noodles are soft and sticky. The appropriate moisture content for stir-fried noodles is 59% to 61%.

Steaming is a key process in the production of instant noodles. The production of hot air dried instant noodles requires a high degree of starch pasting. The steaming time of hot-air noodles is longer than that of fried noodles. Excessive swelling of starch on the noodle surface, which can lead to many processing problems, should be avoided during the steaming process of instant noodle production.2.3. Frying

Most instant noodles are deep-fried. After steaming, the noodle pieces are fed into a frying basket mounted on a moving chain in a tunnel-type fryer. The basket filled with noodle pieces is immersed in hot oil for frying. The frying temperature and time are usually 140-160°C and 60-100 s. The temperature at the outlet of the fryer is usually kept slightly higher than the temperature at the inlet. The frying process should be optimized so that the fried noodles have good organoleptic properties, low fat content and low fat breakdown products. Noodles