Monday, November 23, 2015

Cheesy Chemistry

Now here's the title of an article that sounds like it would make a great teaching and learning tool ..
"Food hacks: The science behind making perfect cheese melts and crispy cookies"
(Sydney Morning Herald, Monday 23rd November 2015)

"Science is great isn't it? ", writes the article's author.
Yes indeed, I couldn't agree more ... looks promising .....

"Even for those of us who find the periodic table of elements a foreign language, we can still reap the benefits of science's life-changing revelations."
Well, that's going a bit far (especially if you happen to teach/learn chemistry), but even so,  it still looks OK ......

"According to science, there's only one type of cheese for your toastie."
...mmm... possibly ...... "science" is rarely capable of making that kind of judgement ..... but we'll continue reading ....

until ........

" That cheese is the one with the right PH to balance the calcium, and release the casein (dairy protein) to create one big soft melty​ mess."
PH? Is that some kind of special food science thing? Could it be phosphorus monohydride?
No, it appears to simply be a mistake, which was, unfortunately repeated on the following line.
The author was referring to pH.

Nevertheless, did you know that different cheeses have different pH values?
I didn't!
So off I went to find the pH of some of my favourite cheeses:
cheese pH
Apparently, pH and temperature are both critical factors in the production of cheese:
  • Addition of starter culture: temperature less than 20°C, pH = 5.1-5.3 (using rennet which contains enzymes for breaking down proteins)
  •  Coagulation: temperature = 30°C, pH = 5.35 - 5.45
  • Pressing: temperature 16-18°C (mild cheeses) or 25°C (hard cheeses), pH = 5.0-5.3
  • Brining in salt solution: temperature 15°C, pH = 5.2
  • Ripening: pH increases to optimum value as given in the table above.
A crumbly cheese, like a Cheshire cheese, has a low pH and low calcium content. At low pH the colloidal calcium phosphate between casein micelles becomes soluble and the size of these protein aggregates decreases, which, makes the cheese crumbly.

A low-acid cheese (high pH cheese) like Swiss cheese, has intact casein micelles which provide an extensive string of protein aggregates giving the cheese more elastic properties.

Further Reading:

Suggested Study Questions:
  1. What is meant by the term pH ?
  2. Calculate the hydrogen ion concentration for each of the cheeses listed in the table above.
  3. Arrange the cheeses in the table from lowest to highest pH.
  4. Arrange the cheeses in the table from lowest hydrogen ion concentration to highest hydrogen ion concentration.
  5. What is an enzyme?
  6. What is a protein made up of?
  7. Why do you think the temperature of the mixture during the addition of rennet and the coagulation stages is higher than at other stages during the production of cheese?
  8. "According to science, there's only one type of cheese for your toastie."
     Do you think science can really tell you the best cheese to use for your toastie? Why or why not?
  9. Who do you think the intended audience of this article is? Explain your answer.
  10. Imagine you have just tested the pH the of various cheeses and that it is your results shown in the table above. Rewrite this article as if it were your lab report.

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