biological indicator evaluation resistometer biological indicator evaluation resistometer a biological indicator evaluation resistometer (bier) vessel is a piece of equipment used to determine the time taken to reduce survival of a given organism by 90% (also known as a log 1 reduction). the name derives from how the equipment is used. a bier vessel evaluates the resistance of biological indicators to moist heat (steam) sterilization. for example, if a 90% reduction is determined to be 5 minutes for the microorganism being evaluated, then a d-value of 5 is assigned. d values are specific to starting bioload, substrate (the material the spores are on), and microbe species. bier vessels typically cost in excess of $100,000, and thus tend to be located where biological indicators are manufactured.