Tuesday, April 16, 2013

Cheese Science!



Milk science, anyway. Last week we got a crash course in the chemistry behind cheese, and got to play around with dangerous acids in the process. We talked about the different results you get from acid vs. lactic curdling, how changes in pH levels affect the structure of proteins and therefore the curds, and how cheese continues to develop through the transformation of lipids and proteins with the actions of molds and bacteria. The professor, Christophe Bressac, also clarified the whole "lactose intolerance" issue, saying that this isn't an allergy, but rather an inability to digest lactose, and with aged cheeses there's no lactose left to cause problems; I knew this, which is why I'd tried to start eating cheese again, and even cow cheese, but found it still caused me problems. He continued though by saying that there are true allergies related to dairy products, and that it's specific to the immunoglobins in milk, and that people will either be allergic to those in cow's milk, or in goat's milk, or any other sort of mammal's milk, but only one at a time. I haven't been tested for specific allergies but since I don't break out in hives when I touch cow's cheese, it can't be that, can it? Finally, there's a "casein intolerance" that he said also causes problems; because butter is mostly milk fats, if I have this particular variety of dairy issue then I should be able to eat butter without a problem, even though I can't eat cheese. Without getting tested, though, it's just easier to take the occasional nibble and probiotic supplement or avoid it entirely. There was no problem avoiding consuming the dairy products in that class, however, especially after we started mixing in the chemicals.


The first thing we did was mix minuscule amounts of calcium chloride and powdered rennet into tubes of pasteurized milk and of UHT milk-in-a-box. We capped the test tubes and put them in a warm water bath to set the curds.

The second test required protective coats, glasses, and gloves, because we were using an industrial-strength acid to lower the pH of the milk (from 6.5 to 4.5) and thereby destabilize the protein chains and separate the fat from the whey and the casein. We set those aside at room temperature.


For test number three, I decided to stay in photojournalist mode rather than research mode, as the test involved mixing sulfuric acid and isoamyl alcohol in with the milk to dissolve the fats and proteins in order to measure the precise fat content of the milk (le taux butyreux du lait). An exothermic reaction produces heat and a nasty black liquid once it's mixed thoroughly; these test tubes went into a centrifuge, and we could see the difference in the amount of clear liquid fat produced by the pasteurized milk (lots) compared to the UHT milk (not as much, though M. Bressac did say that he'd forgotten to shake the box).


We centrifuged the renneted milk, which had had time to start a bit of lactic curdling, as well as the acid-curdled milk, and used pipettes to draw off the whey, which we put in clean test tubes with a bit of Bradford reagent, something that turns proteins blue. There's more of a breakdown of the protein chains with acid, so more proteins end up in the whey, and it turns a darker blue. Or at least it's supposed to - it was a very subtle difference.

If and when I go into cheesemaking as more of a job than a hobby, I will pay more attention to these details. In order to get really standardized cheeses, you need to know the pH of the milk and the fat content in each batch, so that you can adjust precisely the amount of rennet and the speed of the process, and whether you need to use extra calcium chloride to firm up your curd. On the other hand, it's interesting to see the differences that come from milk at various times of the year, and in fact some French cheeses like Beaufort rely on these differences; there's a "summer" Beaufort that gets its flavor from the flowers and herbs the cows graze on in their high mountain pastures, as opposed to the "winter" Beaufort where they're fed on hay. But knowing why cheese happens the way it does is a good thing, and this was definitely one of the more interesting classes we've had.

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