As implied by the name, hand-pulled noodles are made entirely by hand, which is made easier by increasing the proportion of water in the dough to increase elasticity. However, a special kind of grass ash known as蓬灰, or peng hui, is historically added to the dough to make it supple enough to be stretched.
Peng hui, found in rock form, is first smashed into small pieces then cooked in a pot of steaming water for up to four hours, and must be repeatedly watched and stirred to ensure it does not stick permanently to the pot. The water cooked with the 蓬灰is added to the dough, which is then kneaded. The fragrance of the grass also apparently combines with the dough to create a unique flavour that can’t be produced by any other means.
The following video says that only 10% of the restaurants in Lanzhou still use this tried, old method of extraction and that the rest simply use the peng hui in its powdered form. However, as suggested, it is controversial whether the powdered form is in fact the true 蓬灰: http://v.youku.com/v_show/id_XMTk3Njk4OA==.html
After the dough has been covered with plastic and allowed to rest at room temperature to relax the gluten, it is then stretched into a long, thick rope, folded in half, and stretched back to its original length about ten times. By holding the ends of the rope in each hand and allowing the centre to hang down by gravity, the la mian maker flings one side against the other, twisting it to the right, stretching it, folding it in half, then twisting it to the left, stretching it and folding it in half again. This orients the dough fibres along the length of the rope which is necessary to be able to pull the noodles.
Then, on a countertop covered with flour, the maker then pulls the dough, rests it momentarily on the countertop and grabs the two ends with one hand, holding the middle in the other hand. This is continually done until the noodles are of the right thickness. Each time, the noodles are rolled on the countertop with flour to stop them from sticking, and the number of noodles doubles.
Learning the art of the hand-pulled noodle is not easy. These websites illustrate the challenge and torment one can undergo in trying to achieve it:
La Mian in Qingdao
In many la mians in Qingdao, the herb angelica (see above photo) - known in Chinese as 当归 (dang gui) and regarded as beneficial for the blood, liver and stomach - is added to the soup. This alters the taste, and its use in Qingdao is often a controversial point among la mian makers and connoisseurs. According to the poster on the wall at The One with the Dang Gui, angelica - a common ingredient in Chinese medicine - also creates a clear and non-oily soup that is clean and fresh.
Another interesting phenomenon in the old city area of Qingdao is the chain of Ma Jia La Mian (马家拉面) restaurants, some of which are apparently genuine and some of which are not. The unique and distinctive soup is said to include a secret ingredient and tastes completely different to a traditional Lanzhou-style 拉面汤.