The Great Yogurt Experiment – Test 2 Mesophilic Heirloom yogurt

Tasting the bacterial diversity and pH difference by using heirloom yogurt for microbiology teaching.

I love the idea that invisible microbes can change their habitat so much we macroorganisms will pay attention and even help them! After all, people have maintained yogurt cultures for generations. Take for example the Heirloom yogurt from Culture for Health that I have been playing with and am considering sending to my General Microbiology class this semester.

One overarching theme in my microbiology class is always that microbial diversity provides multiple solutions to the same “problem”. Diversity Matters! In this case – different combinations of bacteria can take the same milk, break-up the milk sugars, and poop out lactic acid. The lactic acid lowers the pH of the yogurt, which protects yogurt from pathogenic bacteria (molds can still grow though given enough time). Lactic acid gives the tart, sour taste to yogurt.

To teach my General Microbiology students that microbes – just by growing – can dramatically change their habitat, this semester students will culture their own yogurt! The problem is most store-bought yogurts grow best at 113 °F (45 °C). That’s pretty warm. That was tricky during my first yogurt making experiment when I used a cooler. Not a big deal now in my Instant Pot. I want something simple and successful for the students. They just need to taste and measure the difference! My pre-class survey revealed that NONE of the 50 students have made their own yogurt or any kind of ferment! A few have baked yeast bread, but that’s it! Many students have a minimal kitchen and don’t cook much. Let’s change that!

Cultures For Health‘s mesophilic Heirloom yogurt starters were my go-to. I’ve used and love CFH starter kits several times for my family.

  1. There are 4 heirloom yogurt varieties from different regions (Finland, Scandinavia, and The Republic of Georgia) containing different bacteria with distinct tastes!
  2. Mesophilic means “middle loving”. These bacteria culture yogurt at room temperature! No need for fancy equipment or stress.
  3. It’s easy, works, and tastes good!

Goals and learning objectives

Students will:

1) appreciate how microbes can preserve and enrich foods,

2) experience how microbes physically change their
environment due to their metabolic ability,

3) TASTE the microbial diversity with different mesophilic cultures,

4) make and eat healthy food, while accounting for food insecurity issues and different kitchen resources across a diversity of students.


Students will use 1 cup of milk/yogurt and reserve a glass of milk in the fridge for drinking when the yogurt sets the next day. They will get pH strips to measure the pH before, during, and after the yogurt is curing. In the end, I want them to taste-test the difference between the cultures and get that “a-ha” moment of seeing the pH drop, seeing the milk turn more solid, and tasting the tarty goodness.

Students will receive this package that has 4 different starter packs of dehydrated yogurt bacteria. They will also get pH strips to test the milk and yogurt. Coffee filters and rubber bands will top off the jars. Students will need 5 cups of cold milk (4 for yogurt and 1 to taste the milk the following day) and jars.

Take a look at the videos I’ve done to show the students how easy this is to do with the Cultures for Health cultures and to get them excited!

After the Cultures For Health mesophilic yogurt cultures are set, the pH is checked again. Only 24 hours of bacterial growth, the culture changes from pH 6 to pH 2! Now the milk is healthy, cultured, and preserved as yogurt. Thanks bacterial buddies!

We’ll see how it goes. I’m pretty excited and was thrilled that students responded in the survey that they would LIKE to culture yogurt. We’ll see if I can make this happen with the lab fees that I have to work with! WHEW! I bought starters for every student with lab fees! Wonder if this is the first time lab fees have fed students?

*Disclosure: I only recommend products I have used myself. This post contains affiliate links so that at no additional cost to you, I may earn a small commission to support the cost of the blog. 

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