In our unit on microbes and exponential growth, we learned about the role of microbes in altering flavor and mouthfeel.  One of our favorite microbial foods is cheese:  Cheese would just be spoiled milk if it were not for microbes.

To kick off the class, we challenged the students with a taste test featuring four distinct cheeses:

A) Amish Blue Wheel
B) Emmental
C) Cheddar
D) Port du Salut

We also presented four different types of microbes, and a bit about natural habitats.    Can you guess which microbe belongs to which cheese? Answers below.

1) Propionibacterium (inhabit human skin)
2) Penicillium mold (grow in cool, moderate climate; some species have blue color)
3) Brevibacterium (grow especially well without much personal hygeine)
4) Lactococcus lactis (grow well in acidic conditions)

ANSWERS:

A. 2 – Blue cheeses are inoculated with a strain of Penicillium mold, Penicillium roqueforti. Needles or skewers are used during the inoculation, which is why blue cheeses often have distinct veins running through them.

B. 1 – Emmental is a type of Swiss cheese, which is known for its holes. These holes are bubbles excavated by carbon dioxide, a byproduct of lipid breakdown by Propionibacterium freudenreichii, subsp shermanii. Its close cousin, Propionibacterium acnes, is linked to acne.

C. 4 – Cheddar is an example of a wide variety of cheese types that rely on Lactococcus lactis for the first stage of ripening. L. lactis uses enzymes to produce energy from lactose, a sugar molecule common in dairy products. Lactic acid is the byproduct.

D. 3 – Port du Salut is a washed-rind cheese. The cheese surface is wiped or washed down with a brine that promotes the growth of certain bacteria in the air. A smear of bacteria can be directly applied to the surface to nudge along the process. Brevibacteria linens is commonly used during this inoculation. Ever get a whiff of stinky feet from your cheese? Brevibacteria linens is the culprit, in the cheese and on real smelly feet.