Homemade probiotics

Probiotics in the supermarket are quite expensive, so being able to make them at home makes a difference. Then the question arises: Are you able to make them at home? I don’t have a lab at home, but I’m willing to try.

First, what are probiotics and why do I want them?

Probiotics are bacteria that supposedly can grow in intestines and benefit the host. Research is still being done to really prove the beneficial effects. We all have bacteria in our intestines. If the bad bacteria start to outgrow the good bacteria we get sick. So, as long as the good bacteria have the upper hand it’s all fine. You can read more about probiotics and my visit to the Yakult factory here. For a more official way of looking at probiotics, you can check the NHS.

For this experiment, I’m using two types of probiotic drinks and a regular Greek yogurt for comparison. I am not sure if the Greek yogurt contains live bacteria since a lot of yogurts are treated after fermentation to stop the growth. So now experimental set-up:

My experiment setup:

  • pan
  • wooden spoon
  • 3 jars
  • pH-paper
  • measuring cup
  • Actimel
  • Yakult
  • full-fat Greek yogurt
  • 1L full-fat Dutch milk



Bring the milk to a boil and stir

In the meantime disinfect the jars with boiling water

Put 300 mL of boiling milk in each jar

Let the milk cool off to body temperature

Add the probiotic

Let it stand for 5 days and measure pH to notice changes

Start of the experiment!



The pH of milk changes when bacteria grow in it. Milk gets sourer. In this experiment, the only bacteria growing should be the ones added with the probiotics. So changes in pH mean that the bacteria are really growing.


8h 25 h 82 h 120 h
Yakult 5-6 5-6 5-6 5-6
Actimel 5-6 5-6 5 4
Greek yogurt 5-6 6 5-6 4-5


The results I found for the pH show that I need a more accurate way of measuring and it shows that Actimel has the most acid producing bacteria. Or just the most bacteria.

pH measurement of the three samples
After 25 hours; the paper is used for pH measurement

Next, to the pH, I also looked at the color. Some bacteria have the brightest colors. I wasn’t sure if any of these bacteria would have a distinctive color, but it was worth a shot. It is difficult to describe colors when there are such vague differences. After 30 hours I found a solution: compare the colors to paint samples. By the time I thought of this great idea I was already halfway through the experiment. So it doesn’t really help that much anymore.


0h 8h 25h 82h 120h
Yakult cream darker cream cream hint of sorbet hint of bubbly
Actimel cream cream cream hint of lemon hint of lemon
Greek yogurt light green cream white white hint of lemon white lemon


The table shows that there is a color difference though. It is not a big color difference, but it was visible for me. This is interesting because the bacteria appear to have a very similar name: both Yakult and Actimel are made with L. Casei. The slight difference in name comes after this start. Yakult has the bacteria L. Casei Shirota, whereas Actimel has the bacteria L. Casei Danone. This experiment made it clear to me that they really are different.



Last but not least, I also looked at the viscosity. At this point, I’d really love to have a lab, with all the equipment necessary to measure the viscosity. But I don’t have anything close. So again, we’re stuck with my observations, but my, this result was clear. Actimel resulted in the thickest mess and as a complete opposite, Yakult appeared to become thinner. This again proves that the bacteria are completely different. The change in viscosity also shows that bacteria are growing.



Yes! You can make probiotics at home! The time it takes depends on the type of probiotic you take and the temperature in the room.


What’s next?

After the experiment was finished I left the jars for a while. Now it really is visible that the Yakult bacteria are red or produce something red. The Yakult milk also all of a sudden got really thick. The Greek yogurt with milk showed a separation of a clear yellowish liquid and a white thick layer. I want to experiment further with this and see the differences between the L.Casei Shirota and L.Casei Danone even clearer. And I want to see if the bacteria also grow in soy milk or rice milk. Next time I also want to taste the result. This time I waited too long because I was too busy with other stuff and now it all looks too gross.

Homemade probiotics, a bit of bacteria overgrowth
Yakult with milk after 10 days, can you see the reddish spots in the liquid?


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