A Bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances derived from such organisms. There are many different types of bioreactors including stirred-tank, rocker, airlift and fixed-bed. Traditional multiple-use bioreactors require cleaning after each cell culture run. Smaller-scale bioreactors are glass systems and can be sterilized in an autoclave. A bioreactor is a manufactured device where a biological reaction is carried out. Bioreactors are usually cylindrically shaped and range in different sizes from litres to cubic metres. They are commonly made of stainless steel. Bioreactors are used for making pharmaceutical products such as antibiotics and insulin. Bioreactor design is a relatively complex engineering task, which is studied in the discipline of biochemical/bioprocess engineering. Under optimum conditions, the microorganisms or cells are able to perform their desired function with limited production of impurities.