Downstream processing is primarily concerned with the initial separation of the bioreactor medium into a liquid phase & a solid phase and subsequent separation, concentration & purification of the product. Chemical engineering principles play a vital role here, as well in terms of designing and operation of the separation systems. Downstream processing costs can be as high as 60 - 70% of the selling price of the product as exemplified by the plant Eli Lilly built to produce human insulin. Over 90% of the 200 staff are involved in the recovery processes. Downstream processing represents a major part of the overall cost of most processes, but is also the least glamorous aspect of biotechnology. Improvements in downstream processing will benefit the overall efficiency and cost of processes and will make the biotechnology competitive to the conventional chemical processes. Downstream operations can play catch-up through conventional capacity-expanding strategies, for example by scaling up downstream equipment, employing multiple controllers for more rapid cleaning between steps, running fewer purification cycles (by scaling up column dimensions) or using media with higher throughput or binding capacity. Each solution has its benefits, as well as costs.