Fermented old dough (also known as old fat, flour fat, old yeast, etc. ) is a relatively primitive fermentation method, relying on wild yeast and various miscellaneous bacteria (lactic acid bacteria, acetic acid bacteria, etc.) for fermentation. ) make the dough swell. These bacteria and other miscellaneous bacteria will inevitably produce some substances and components harmful to human body. The bad sour taste produced by the fermentation of old noodles must be neutralized by adding alkali. The amount of alkali is not easy to master: too little alkali will make flour products sour and affect the quality; Too much alkali will combine with isoflavone pigment in flour and make flour yellow. At the same time, the addition of alkali will seriously destroy the nutrients such as B vitamins in dough.