Testing the Viability of Yeast

Several different treatments are used to autolyse yeast cells. The viability of the autolysed yeast is then tested by: plating out on agar; testing for dehydrogenase activity; microscopic examination with methylene blue.

Background
In the food industry, yeast is grown in huge fermenters and then given different treatments to produce different flavourings. All of these treatments involve the process of autolysis. This process of autolysis (auto-self; lysis-splitting) involves killing the yeast and encouraging the breakdown of the cells by enzymes.

It is the products of enzyme degradation which produce the specific flavour molecules. Autolysis usually begins with the addition of salt to the cells, causing water to leave the cells by osmosis and beginning the process of cell breakdown.

The cells are then heated encouraging further breakdown of the cells. In this experiment different treatments are used to autolyse yeast cells before testing the viability of the yeast cells.