There are intrinsic factors (pH, a w ' antimicrobials) and extrinsic factors (temperature, atmosphere) of foods that affect the growth of microorganisms. In the laboratory, traditionally, these factors were studied individually. The current trend in food preservation is "hurdle technology." In hurdle technology, multiple intrinsic and extrinsic factors are used together to create a synergistic barrier to prevent microbial growth. One factor that makes evaluating hurdle technology difficult is that the results of combinations of factors are unpredictable. In addition, the testing of multiple factors often involves complex preparation of many different media formulations.