After reading the online sources and McGee’s chapter on Milk and Dairy products, I can’t stop thinking about how much is going on in the block of cheddar cheese in my refrigerator. There’s so much biology and chemistry to explain this magical food!
Two facts that stood out to me:
1. The golden color that we tend to attribute to “wholesome”dairy products? It’s actually contingent upon the amount of carotene that cows convert to vitamin A– cows that don’t convert that much carotene produce more golden-colored milk. This depends on the breed of the animal. Guernsey and Jersey cows produce golden milk, while sheep, goats, and water buffalo produce very white milk. (Which becomes white butter and white cheese, etc.)
2. We’ve learned in past chemistry courses that H+ is an acid, but now we can put that in the context of curdling milk. When the pH of milk is lowered by adding an acid, two things happen:
- First, the negative charge of the capping-casein is neutralized by the addition of H+. This means that the micelles in milk stop repelling each other and begin to loosely form clumps.
- Next, as the pH continues to drop, the casein proteins actually lose their negative charge completely and bond together to form what we recognize as curdling: the proteins form a continuous network.
That’s why, for example, adding lemon juice to a butter-based batter causes the batter to curdle– the proteins in the melted butter lose negative charges and coagulate.
I’m looking forward to learning more about the chemistry and microbiology of cheese tomorrow!