Tasting the bacterial diversity and seeing pH difference using yogurt fermentation for microbiology teaching. I love the idea that invisible microbes can change their habitat so much we macro-organisms will pay attention and even help them! After all, people have maintained yogurt cultures for generations. Take for example the Heirloom yogurts 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 to see and taste the difference! The problem is most store-bought yogurts grow best at 113 °F (45 °C). That’s pretty warm. That was tricky during my