Phenol red broth with carbohydrates are used for the determination of fermentation reactions in the differentiation of microorganisms.

• Complete medium
• Detect acid production
• Used as negative control for fermentation

Most of the end products of carbohydrate fermentation are organic acids which, in the presence of phenol red, produce a color change in the medium from red to yellow.

If gas is produced during the fermentation reaction, it is collected in the inverted Durham tube.