Abstract 013
Factors Affecting Dissolved Oxygen Analysis in Beer and Water
J. Amer. Soc. Brew. Chem. 39: 147-153, 1981
T.J. Wisk, J.T. Weiner, and K.J. Siebert
A number of chemical and instrumental dissolved O2 techniques were studied for their response to added O2 as well as to factors other than O2 (pressure, flow, SO2, Cl2, and pH). Polarographic (IL 531, IL 540, IL 545) and galvanic (Hays meter) instruments showed similar increases in output with added O2 (in beer), but the galvanic instrument gave different absolute values. The difference in absolute values was largely caused by the indigo carmine calibration technique (used to calibrate Hays meters), which responds to species other than dissolved O2. Pressure and flow rate had little effect on polarographic instruments, provided the O2 concn. was below saturation. The Hays meter output decreased with decreasing flow rate. Decreasing the pH of water by addition of phosphoric acid lowered the apparent O2 content as assessed by the Winkler and IL 531 methods, whereas the Hays method showed an increase. Chlorine in water caused an apparent O2 increase with the Hays meter and a decrease with the IL 531 analyzer. SO2 in water produced an apparent O2 increase with the IL 531 analyzer. Calibration of the Hays meter near the low end of its range produced low O2 results. When an ”offset” was introduced in the calibration procedure, performance of the Hays meter improved. A single offset value was not useful with all Hays meters, as each instrument examined had a somewhat different response to O2.
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