Chinese Noodles.
Add a teaspoon of 碱水 to noodle dough and it turns yellow, firm and springy, and smells faintly of eggs — though there is no egg in it.
Wheat noodles are flour, water and usually salt, kneaded, rested, and cut, pulled or extruded. Alkaline noodles add 碱水 (kansui): a solution of sodium and potassium carbonates. The high pH changes three things. Gluten proteins cross-link more tightly, so the noodle is firm, springy and slippery and holds up in hot soup (VI.10). The flour's flavonoid pigments, colourless at neutral pH, turn yellow in alkali — the colour of ramen, 碱水面 and wonton noodles, without egg. And the alkali gives a faint, mineral, eggy smell. Too much makes noodles soapy and bitter. Salt in noodle dough also tightens gluten and seasons.
Rice noodles (米粉, 河粉, 米线) are a different material: rice flour has no gluten, so the dough is steamed into sheets or extruded and cooked, and its starch, gelatinised and then retrograded (VII.3), holds the strands together. Dried rice noodles are soaked before cooking; fresh 河粉 is fried hot and fast so it does not break. For both kinds, cooking in plenty of boiling water and then rinsing or plunging in cold water (过冷水) removes surface starch and stops the cooking, giving firm, separate strands for cold dishes and stir-fries. The workshop mixes kansui.
Below: the pH of the water in a noodle dough from the kansui (as sodium carbonate) and hydration you choose (carbonate hydrolysis, exact for the solution; the flour buffers the real dough about a unit lower), with the colour the flour's pigments would take.
- Explain what kansui does to noodles.
- Tell alkaline noodles from plain ones.
- Handle rice noodles.
- Cook and cool noodles for each use.
Alkali for spring, starch gel for rice
One per cent kansui in a dough at 35 % hydration gives the dough's water a pH of about 11.9 before the flour buffers it; half a per cent about 11.7. Even small amounts move the pH by four or five units because carbonate is a strong base in water — which is why recipes measure kansui in grams and why a little too much tastes soapy. A home substitute is baked baking soda: soda heated at 120 °C for an hour turns partly into sodium carbonate.
Cooking noodles: use plenty of boiling water and keep it boiling; fresh wheat noodles cook in 1–3 minutes, dried in 3–8. For noodle soups, cook the noodles separately so their starch does not cloud the broth, and put them in the bowl just before the hot soup. For 凉面 and stir-fries (炒面), drain, rinse in cold water (过冷水), drain well and toss with a little oil so they do not stick. Rice noodles: soak dried ones in warm water until pliable, then cook briefly; fry fresh 河粉 over very high heat in a well-oiled wok, moving gently, for 干炒牛河 (XV.5).
Make two small batches of noodle dough, one with a pinch of baked baking soda dissolved in the water. Rest, roll and cut both, cook them, and compare colour, smell and bite.
Terms
- 碱水 (kansui)
- Alkaline water of sodium and potassium carbonates for noodles.
- 过冷水
- Rinsing cooked noodles in cold water to stop cooking and remove starch.
- Rice noodles
- Noodles held together by set rice starch, without gluten.
- Flavonoids
- Flour pigments that turn yellow in alkali.
Sources
- CRC Handbook of Chemistry and Physics: solubility of calcium hydroxide 1.73 g/L at 20 °C, falling to about 0.66 g/L at 100 °C; sodium carbonate pKa2 (bicarbonate) 10.33 at 25 °C.
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
- H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.