The main reason of nutritional loss of steamed bread is adding alkali to fermented dough. Vitamin B 1 in flour is relatively stable in acidic environment, but it is easily destroyed in alkaline environment. If too much alkali is added or alkaline leavening agents such as soda are used to make steamed bread, most of the vitamin B 1 in the dough will be destroyed.

Wheat flour is used as raw material and fermented by yeast. The dough at this time is called "fermented noodles". If pure yeast is used for fermentation, there are few or no miscellaneous bacteria and no sour taste, and steamed bread can be directly processed without adding alkali. But people often use old flour to ferment and add alkali before they can be processed into steamed bread. At this time, adding alkali should not be excessive.

Proper addition of alkali can make the dough sweet and sour, and the steamed bread steamed by heating once will be soft, white and delicious. Why must steamed bread be mixed with alkali when fermented with old flour? Because the old yeast contains many miscellaneous bacteria, mainly acetic acid bacteria. When the temperature in the dough reaches 33℃, acetic acid bacteria also multiply and secrete oxidase with yeast fermentation. Oxidase oxidizes the dilute alcohol in the dough into acetic acid and water, which makes the dough have a strong sour taste and become softer and worse. The longer the fermentation time, the stronger the sourness of dough, so alkali must be added to neutralize the sourness. However, when adding alkali, the amount of alkali must be accurately determined, so that the surface of alkali can completely react with acetic acid in dough to produce sodium acetate, carbon dioxide and water, which can remove its sour taste. It can be seen that the dosage of alkali is the key to ensure yeast products. If too much alkali is added, it is called heavy alkali, which will make the product yellow in color and bitter in taste, and will destroy a lot of vitamin B 1 in dough. Therefore, when making steamed bread, you should add an appropriate amount of alkali.

Correct alkali preparation should be flexibly controlled according to yeast size, tenderness, temperature, fermentation time, yeast dosage and product requirements. After experiments, every 0? 5 kg of fermented noodles with 3? 7~4? 3 grams of alkali neutralization, acidity at pH6? 2~6? 6. The average vitamin preservation rate of steamed bread is 80%, which is delicious and easy to digest. Of course, fermentation with pure yeast can avoid adding alkali and can be directly made into steamed bread. The above analysis is a reminder for people to make steamed bread with old noodles.