By Harold McGee
The standard thick Japanese noodles (2–4 mm in diameter), called udon, are descendents of the Chinese white salted noodle. They’re white and soft and made from soft wheat flour, water, and salt. Ra-men noodles are light yellow and somewhat stiff, and are made from hard wheat flour, water, and alkaline salts (kansui). Very thin noodles (around 1 mm) are called so-men. Japanese noodles are usually cooked in water of pH 5.5–6, which is often adjusted by adding some acid. After cooking, the noodles are drained and washed and cooled in running water, which causes the surface starch to set into a moist, slippery, nonsticky layer.