Noodle production starts with dissolving the salt, starch, and flavoring in water to form a mixture that is then added to the flour. The dough is then left for a period of time to mature, then for even distribution of the ingredients and hydration of the particles in the dough, it is kneaded. After it is kneaded, the dough is made into two sheets compounded into one single noodle belt by being put through two rotating rollers. This process is repeated to develop gluten more easily as the sheet is folded and passed through the rollers several times. This will create the stringy and chewy texture found in instant noodles. When the noodle belt is made to the desired thickness by adjusting the gap in the rolls, it is then cut right away. Wavy noodles are made in a slow-paced conveyor belt and are hindered by metal weights when coming out of the slitter, which gives the noodle its wavy appearance. If the strands are to be molded into other shapes, liquid seasoning can be added as well. Once the noodles are shaped, they are ready to be steamed for 1–5 minutes at 100 °C (212 °F) to improve texture by gelatinizing the starch of the noodles. When steaming, the addition of water and heat breaks up the helix structure and crystallinity of amylose. Amylose begins to diffuse out of the starch granule and forms a gel matrix around the granule.[23] Noodles can be dried in one of two ways: by frying or by hot-air drying. Fried instant noodles are dried by oil frying for 1–2 minutes at a temperature of 140–160 °C (284–320 °F). The frying process decreases the moisture content from 30–50% to 2–5%. Common oils used for frying in North America include canola, cottonseed, and palm oil mixtures, while only palm oil or palm olein are used in Asia.[citation needed] Air-dried noodles are dried for 30–40 minutes in hot air at a temperature of 70–90 °C (158–194 °F), resulting in a moisture content of 8–12%. During the drying process, the rapid evaporation of water creates pores throughout the food matrix, which allows for short cooking times in the finished product. In the case of fried noodles, the creation of pores is directly related to the uptake of fat into the noodles.[24] More than 80% of instant noodles are fried as this creates more evenly dried noodles than hot-air drying, which can cause an undesired texture in finished noodles and also takes longer to cook.[citation needed] However, with fried noodles, the oil content is about 15–20% and decreases the shelf life of the noodles due to oxidation, whereas in hot-air dried noodles, oil content does not go above 3%.[22] Seasoning sachets on instant noodles, the content of a Japanese instant yakisoba package Before packaging with seasoning, the noodles are cooled after drying, and their moisture, color, and shape are checked. Packaging of the noodles includes films impermeable to air and water. There are two forms of packaged instant noodles: one with the provided seasoning in small sachets inside or in a cup with seasoning on top of the noodles. There are a variety of flavors to the noodles, depending on which ones are added to the seasoning. Such flavors include beef, chicken, pork, shrimp, etc. In instant noodle cups, soy protein and dehydrated vegetables and meats are often added for further flavor.[citation needed] The shelf life of instant noodles ranges from 4–12 months, depending on environmental factors. Their stability comes from the high sodium content with low moisture, and low water activity. Instant noodles can be served after 1–2 minutes in boiled water or soaked in hot water for 3–4 minutes.