Protocol for Practical Classes

Subject: Testing the fermentating activity of the yeast

Experiment 11 – characterization

Materials:

Provided by the students:

Baker yeast

Knife

Metods:

1.To differ the two assay tubes, write LY (live yeast) and DY (dead yeast) in each one.

2.Do the same to the Durham tubes.

3.Prepare an Yeast solution 1 with a spoon (little one) of suggar, 75mL of distilled water and 1/8 of the cube of baker yeast.

4.Prepare and Yeast solution 2 with 2 spoons of sugar, 25mL of distilled water and 1\4 of the cube of baker yeast.

5.Fill in the assay tubes with the solution 1 (3cm from the edge must be empty).

6. Fill in the Durham tubes with the solution 2 (untill the edge).

7.Put the Durham and the assay tube named DY in the warm-bath for 20 min.

8.Them put the Durham tube, up-side down, inside the assay tube.

9.Do teh same with the two LY tubes (Durham and assay tubes).

10. Observe the tubes for 1o min, writting down the observed results. Measure the Durham distance from the bottom of the assay tube each one or two minutes and put the values on a table.

11.Measure the pH in each tube after 50minutes.

Objectives:

To prove the fermentation occurrence.

To identify the products obtained agter this process.