I have already applied in this university for masters in biochemistry but got rejections and no reason written. So can you tell how to successfully get admission in German universities?

Biochemistry studies biological molecules, their roles within the cells, and the chemistry of the reactions of molecules within living structures. Biochemistry is a valuable course that provides career opportunities in hospitals, food institutes, universities, cosmetic laboratories, and some drug recovery centres. 

To get admission in Masters of Biochemistry, students need to meet the given eligibility criteria, including:

The student must have completed their 12th class. However, no cutoff has been mentioned regarding this. 
The student is required to have a Bachelor's degree with decent scores completed from a recognized university. 
The student should have obtained a minimum of 6.5 scores on the IELTS test. 

In your case, you might have received rejection as you must have failed to meet one or more eligibility requirements mentioned above. Therefore, ensure you fulfil all the conditions to pursue Masters in Biochemistry.

The master's in Biochemistry is a 2-year long program designed to equip students with the necessary knowledge and skills. Some of the well-known Universities offering Masters in Biochemistry in Germany are: 

Heidelberg University
University of Bonn
Technical University of Munich
University of Gottingen
University of Cologne