Bread yeast is divided into yeast, active dry yeast and fast active dry yeast.

Compressed yeast: a bulk containing 70 ~ 73% of water produced by saccharomyces cerevisiae. Light yellow, compact structure and easy to crush, with strong hair surface capacity. At 0 ℃ can preserve 2 ~ 3 months of the product was originally in the plate and frame filter press the yoghourt squeezing after centrifugal dehydration, so called pressed yeast, commonly known as yeast. Fresh compressed yeast should not be refrigerated for too long. If preserved for too long, the yeast will start to brown and the effect of yeast as a leavening agent will be reduced if the refrigerating period is prolonged. , increase its dosage is 1 ~ 2% of the amount of flour, baking temperature for 28 ~ 30 ℃, if the temperature is more than 54 ℃, the activity of yeast will lose. Time of dough varies with yeast dosage, temperature of dough and sugar content of dough, generally 1-3 hours.

Active dry yeast: dry yeast with water content of about 8%, granular, with hair surface capacity. Fresh yeast was obtained by culture of yeast with dry resistance and stable fermentability, and then made by extrusion molding and drying. The fermentation effect is similar to that of the pressed yeast. The products are packed in vacuum or aluminum foil bags or metal cans filled with inert gases (such as nitrogen or carbon dioxide). The shelf life is from half a year to one year. Compared with the compressed yeast, it has the advantages of long storage period, no low temperature storage, convenient transportation and use.

Fast active dry yeast: a new type of fine granule (diameter less than 1mm) with fast and efficient fermentation. Water content is 4-6%. On the basis of active dry yeast, high drying resistance of saccharomyces cerevisiae was obtained by using genetic engineering technology. Like active dry yeast, it is vacuum or filled with inert gas and has a shelf life of more than 1 year. Compared with active dry yeast, the grain size is small and the fermentation power is high. When used, it does not need to be hydrated first, but can be directly mixed with flour and water to make a dough for fermentation. After fermentation, it can be baked into food in a short time.

Jul.07, 2018