Fig. 2A: Using the pH Indicator Phenol Red to Detect Acid

Fermentation tube before inoculation.
Fermentation with acid but no gas.
Acid end products from carbohydrate fermentation lower the pH causing the pH indicator phenol red to turn from red (alkaline) to yellow (acid).
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Microbiology Laboratory Manual by Gary E. Kaiser, PhD, Professor of Microbiology
is licensed under a Creative Commons Attribution 4.0 International License.
Last updated: September, 2017