- Increase in turbidity of the medium, medium becomes cloudy.
- Initial stages of yeast contamination are difficult to detect macroscopically, as the pH changes only slightly, initiating little or no color change in medium containing phenol red as pH indicator.
Yeasts can be visualized using phase contrast at 100x - 400x magnification. Phase contrast facilitates detection, especially at low contamination levels. Yeasts appear as ovoid bright particles between the cells. They can exist as single cells or in in the form of chains or branches.