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Baker's yeast is a single-cell eukaryotic microorganism, which belongs to Saccharomyces cerevisiae. It is closely related to humans and is the earliest microorganism applied in human life practice. It is also an important microorganism in modern fermentation industry.It USES fermenting sugar in the dough or trehalose and liver sugar in the cells to grow and reproduce, producing carbon dioxide gas, making the dough inflated and fluffy, so as to achieve the purpose of dough porosity.Therefore, yeast is an indispensable microbial loosening agent in bread production, and also the basic raw material of bread products. Yeast production has a history of more than 200 years.Highly active dry yeast is a yeast cell product that exists in solid form but does not lose its activity.It has three basic characteristics: first, it can be stored at room temperature for a long time without losing its activity;Second, after rehydration under certain conditions, highly active dry yeast can return to its natural state and have normal yeast activity.Third, the cell content exceeds 20 billion cfu/g and the water content is less than 6.0%.High activity bread dry yeast also has the advantages of longer storage time and more convenient use.At present, the technology of high-activity dry yeast produced from glucose molasses is not mature enough. After dehydration, the activity of the product is greatly reduced, the dryness is not resistant, the storage capacity is low and the shelf life is short.Therefore, the main content of this research is to improve the fermentability and preservation ability of active dry yeast.In this study, different strains of yeasts were used to prepare active dry yeasts and the fermentation attenuation was studied.The optimal strain was used as the starting strain to study the fermentation attenuation under different preparation methods and storage methods.By analyzing the production and yield of insoluble substances such as trehalose in yeast cells, the mechanism of fermentation attenuation was analyzed.The results showed that the trace elements contained in glucose molasses were less and the nutrition was not rich.The cell particles are not full, the size is not uniform, the impurity is more, the degree of fragmentation is big;The component of cell elements contains less Mn, Fe, Zn and other trace elements which are beneficial to the preservation of dry yeast. Therefore, the fermentation activity is low and the storage is not resistant.The contents of nitrogen, phosphorus, trehalose and water in dry yeast have great influence on its activity and storage.The results showed that the content of trehalose in dry yeast cells was about 12%-14%, the content of phosphorus (calculated by P205) was 35%-40% of nitrogen, the content of water was 5.o % -6.0%, and the product had good storage stability.The addition of 2.5% spool 60 and 2.0% vitamin C had a good protective effect on the vitality and preservation of dry yeast.By studying the physical and chemical characteristics, drying temperature, storage temperature and packaging mode of dried yeast, it was found that the products with light yellow color and even granules were preserved by vacuum or nitrogen in the cold storage under the drying temperature of 40℃, which could obtain higher vitality and retention rate.Through orthogonal experiment and response surface analysis experiment, further optimization, water content 5.5%, dish 60 concentration 2.6%, vitamin C concentration 2.0%, drying temperature 40℃, the vitality and preservation rate of active dry yeast has been improved.