Science Models
Science Fair Projects

Dairy Products and Bacteria

Published on Sep 16, 2023


The objective: In my project, I tried to determine which dairy product would have the most aerobic bacteria. I used ryazhenka, kefir,sour cream,yop yogourt,and bio-k yogourt.
In order to actually do my experiment I used methylene blue. I hypothesised that the bio-k yogurt would have more aerobic bacteria and I was right.

The purpose is to find out which dairy product has more bacterial content- kefir,ryazhenka,bio-k yogourt,sour cream,and yop drinkable yogourt


I think that the bio-k yogourt has more bacterial content.


1. 6 mini bottles with lids

2. 12 drops of methylene blue solution (using a pipette)

3. Pipette

4. 10 ml of kefir

5. 10 ml of bio-k yogourt

6. 10 ml of yop drinkable yogourt

7. 10 ml of sour cream

8. 10 ml of ryazhenka


1. Pour 10 ml of kefir in the small bottle.

2. Pour 10 ml of ryazhenka in the small bottle.

3. Pour 10 m of yop yogourt in the small bottle.

4. Pour 10 ml of bio-k yogourt in the small bottle

5. Pour 10 ml of sour cream in the small bottle.

6. Using the pippette add 2 drops of the methylene blue solution to each test tube in order for it to react and change colour to tell you how much areobic bacteria is in the dairy product.

7. Wait 15 min until this happens. If it takes more than 8 hours for the dairy product to change back to its original colour, the quality is excellent. If it takes 5.5 to 8 hours, then there are less than 0.5 million organisms/ml. If it takes 2 to 5.5 hours for the dairy product to change back to its original colour, then there are 4 to 20 million organisms/ml. If it takes less than 20 minute ,then there are over 20 million organisms.

8. Record your results.

Dairy Products

Dairy Products


Dairy Products

From the chart you can see that sour cream,ryazhenka, and kefir changed about the same amount. Then,you notice that the bio-k yogourt had the most aerobic bacteria and Yop yogurt had the least. I knew that the bio-k yogurt would have more aerobic bacteria because the package said that it was made with a lot of bacterial content. As for the rest of the prodcts I didn't have a clue for the results, so it was very interesting to find out. For the bio-k yogurt the colour was almost white, meaning it had a lot of aerobic bacteria. The yop yogurt colour stayed almost 100 percent blue. The sour cream, ryazhenka, and kefir turned a sky blue colour meaning it had a mdium amount of aerobic bacteria


An aerobic organism is an organism that can survive and grow in an environment that has oxygen. Methylene blue is a blue dye that reacts when there is no oxygen in a sample by turning translucent. Methylene blue is a good product for finding the aerobic bacteria in a sample because aerobic bacteria use up oxygen. In the end, my hypothesis was correct, the bio-k yogurt does have the most aerobic bacteria out of the products that I used.

The reason why the bio-k yogurt had more bacterial content was because the company originally makes it like that. Some dairy products can have less bacterial content because they may be heated at 80 degrees celcius or they may kill any pathogenic bacteria or take away all of the mil's proteins with a process called denaturing. Denaturing is mainly formed on yogurt and this is the reason wjhy some dairy products have less bacterial content than others..

Science Fair Project by Sofia Amanda Puscareov