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Cheesy Science

April 21, 2010

This post is quite science intensive, so try to hang on! I designed the text and upcoming lab for 10th-11th grade chemistry, so it’s accessible.  Part two will be the lab portion which may or may not involve homemade cheese. 😉

I still can’t eat cheese, but the research was fascinating! I can definitely see where dairy science is an entire class, and even an entire major at some schools!

So, fellow science geeks, enjoy…

Milk is an amazing substance composed of water, protein, fat, sugars, and other trace minerals. It has been harvested as a source of human nutrition since the beginning of time from all different kind of animals: sheep, goat, buffalo and most commonly, cows. The amazing thing about milk is its various properties that make it perform cool “tricks” and provide humans with nutritious products.

One of the most interesting milk trick, and the process we will be focusing on today, is the formation of cheese from cow’s milk. Cheese is a solid or semisolid substance made from draining the whey after the coagulation of milk’s major protein, casein. So, what does that mean?

We established milk contains proteins. What are proteins? “Proteins are molecules made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains. There are 20 different types of amino acids that can be combined to make a protein. The sequence of amino acids determines each protein’s unique 3-dimensional structure and its specific function.” ("Chymosin (Rennin) and the Coagulation of Milk.") The major proteins in milk are casein and whey. There are also a bunch of different forms of casein and whey, alpha-s1, alpha-s2, beta, and kappa casein and the most predominate whey protein are beta lactoglobulin and gamma lactalbumin. We’re most concerned about the casein at this point though. The alpha and beta caseins are hydrophobic- think of phobic as fear, and hydro as water- so they DON’T want to mix with water. They are readily precipitated by calcium– this means that calcium (which we all know is in milk thanks to the Got Milk? campaign) is going to make these alpha and beta proteins a solid product. So why doesn’t milk have chunks of alpha and beta casein on the bottom? This is thanks to our kappa caseins! Kappa casein is not calcium precipitatable- so it’s not going to do separate out like alpha and beta. Now, think of all these caseins as pipe cleaners. They are all tangled around each other in a big knot-like thing, so the kappa keeps the calcium from making the other caseins into precipitates. So, Kappa is our big hero, keeping casein soluble.

cheese is great how is cheese made

So what’s kappa’s arch nemesis? CHYMOSIN! Also known as rennin, chymosin is an enzyme that denatures our hero, kappa. So think of a big pair of scissors- these are the rennin enzyme, and they’re going to cut that nice big fuzzy pipe cleaner, kappa, that’s keeping all the other pipe cleaners (alpha and beta) together.

string cheese cut the cheeserennin scientific diagram

When the rennin snips the kappa-casein, its little pieces are turned into a smaller protein, called micropeptides. Para-Kappa-Casein, the new little pieces, don’t have the ability to hold together the other caseins anymore and protect them from calcium, which makes them into solid products. So what happens?

They become precipitates! They’re called curd, and this process is called curdling. You’ve probably heard this term before- commonly in terms of milk when it’s added to coffee, or when you add lemon and milk to tea. Why would this happen without rennin? We’ll get into that a little later.

poor cow got milk

Right now- a little more about chymosin, or rennin. This enzyme comes from the stomachs of baby cows. When calves drink milk from their mother, it’s their life source- they receive all they need from this milk. The enzyme in the stomach coagulates (another term for the curdling) the milk so it doesn’t rush through the stomach so quickly, and the calf gets a chance to digest the proteins breaking them up into amino acids to build their cells. Rennin works best in a slightly acidic environment, just like a cow stomach.

Alright- now revisiting the coffee scenario. There is more than one factor that can denature kappa-casein. Nothing performs as well as rennin, but other factors also work- like the addition of an acid, salts or phenols. Heat can speed up the reaction that occurs. The acidic cup of hot coffee can easily curdle your milk and leave you with yummy chunks. (cheesy coffee!)

the worst coffee eversad stains

 

 

So Casein makes curd, and curd makes cheese.

 

Why then, are there hundreds of varieties of cheeses?

The casein precipitate can be strained out with cheese cloth, but what happens from there makes a world of difference.

More than you want to know about cheese varieties:

First of all, the type of milk used to begin the experiment is crucial to the final product. The milk fat content (skim, 2%, whole, etc.) makes as much of a difference as the type of animal it’s from (cow, sheep, goat, buffalo) and the animals diet matters, as does the pasteurization (killing of bacteria) method, or if it was pasteurized at all. The method to produce the curd varies, as previously stated. Enzymes and acid are commonly used, but the introduction of bacteria, which convert the milk sugars into lactic acid, accomplish the same task and play a large role in the finished flavor. The bacteria in Swiss cheese produce carbon dioxide gas which gives Swiss its characteristic holes.

When the curd is strained, it can be served un-ripened.

Variations of fresh cheeses include cottage cheese, mascarpone, cream cheese, Petit-Suisse, and quark. The curd can be stretched and kneaded to make varieties like mozzarella and Provolone.

 Soft cheeses are ripened for a short period of time and are rarely used in cooking because they lose flavor with heat.

Surface ripened soft cheeses are coated with a layer of mold and this forms a rind with a pronounced flavor (like brie).

Interior ripened soft cheeses are washed in a brine (salt and water mixture) and ripened. This produces cheeses like Munster and Livarot.

Semi-firm cheeses are pressed curds that ripen for a longer period of time; this category includes cheddar, Gouda, Fontina, and Monterey Jack.

Firm (hard) cheeses are typically cooked, pressed, and aged. Gruyere, Parmesan, and Romano are all common hard cheeses and they are firm, usually with a dry flavor.

Blue cheeses are cheeses where the curd is cut and molded, drained, salted, and inoculated with a mold. The mold ferments the cheese and produces blue veins. Gorgonzola, Roqufort, and Danish Blue are all produced this way and are often crumbly with a peppery flavor.

 

Questions to review

1. What proteins in milk are hydrophilic, which ones are hydrophobic?

In milk, Alpha and Beta-Casein are hydrophobic and Kappa-Casein is hydrophilic. The whey proteins are also hydrophilic.

2. How are the hydrophobic proteins precipitated, and what keeps them soluble? How do they become insoluble?

Calcium precipitates the hydrophobic Alpha-Casein and Beta-Casein. They remain soluble because their interactions with Kappa-Casein and the macro-casein molecule they form. When Kappa-Casein is denatured by acid, enzyme, or another source, there is nothing to keep the other casein molecules from becoming precipitates

3. Explain why one either puts lemon in their tea or honey in their tea, but never both.

The addition of an acid to milk can denature kappa-casein, especially at higher temperatures. Hot tea is typically acidic and has a tendency to curdle milk, especially if an acidic ingredient like lemon juice is added.

4. What enzyme is predominantly used in cheese making, where is it harvested from, and explain its significance in its original location as well as in the cheese making process.

Rennin is the enzyme harvested from dried calves’ stomachs that denatures kappa-casein and creates curd. In the calves’ stomach, rennin converts milk to a semi-solid so it can remain in the stomach longer and the proteins can be fully digested. It has the same effect to milk outside of the stomach, denaturing Kappa and coagulating Casein.

5. “Non-dairy” coffee creamer’s active ingredient is typically caseinate (coming form milk). Caseinate whitens and emulsifies coffee, making it creamy, and it is preferred many times over dairy creamers because it doesn’t curdle. Explain why this phenomenon.

Sodium caseinate is a product of milk. Because it is already an isolated protein, there is no worry about it curdling in a hot or acidic environment. Caseins are good emulsifiers, meaning they help to keep fats suspended in water-based products. Other ingredients of nondairy creamer typically include corn syrup solids (a sweetener) and vegetable oil, suspended by the caseinate. Casinate is actually hydrophobic but the addition of calcium or sodium ions (calcium caseinate, sodium caseinate) can make it soluble in water.

Sources

"Chymosin (Rennin) and the Coagulation of Milk." arbl.cvmbs.colostate.edu. 30 Jan. 2009 <http://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/rennin.html&gt;.

"IFT Experiments in Food Science Series." Access Excellence @ the National Health Museum. 30 Jan. 2009 <http://www.accessexcellence.org/AE/AEPC/IFT/unit_three.php&gt;.

Perdue Research Foundation. "Unit 3. Proteins." IFT Experiments in Food Science Series 3 (2000): 1-22.

"What are proteins and what do they do? – Genetics Home Reference." Genetics Home Reference – Your guide to understanding genetic conditions. 30 Jan. 2009 <http://ghr.nlm.nih.gov/handbook/howgeneswork/protein&gt;.

The Visual Food Encyclopedia: The Definitive Practical Guide to Food and Cooking. New York: Macmillan, 1996.

~~~

So I think I chose a college! 😀 I’ll announce which one the first of May, but I’m very excited. And I’m 10 whole days early… Who am I?

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12 Comments leave one →
  1. April 21, 2010 8:55 am

    My first degree was heavy in food science, organic chemistry, etc. We did the whole “extracting the whey,etc , ” deal….labs give me nightmares…there were many beakers broken by me..absolute nut case.

    • April 21, 2010 8:58 am

      Ohh Nut Jar! haha I bet you were wonderful. 🙂

  2. April 21, 2010 9:29 am

    Wow girl, you are SMART!!!! Go you!!! I barely hung in there 🙂
    YAY on choosing the college! I can’t wait to hear which one you picked!

  3. April 21, 2010 9:53 am

    How do you know all this info? They can’t be teaching you that in high school, can they?

    I cannot wait to hear about this college choice!

  4. April 21, 2010 5:39 pm

    I can’t wait to hear your college decision. 🙂

  5. April 21, 2010 7:12 pm

    Congrats on the college decision!! Can’t wait to hear which one you chose 🙂 Interesting stuff about milk- especially the differences between all the cheeses!

  6. Katherine: What About Summer? permalink
    April 21, 2010 8:07 pm

    I’ve always wondered about casein! it’s so interesting lactose intolerance types and who can/cannot tolerate whey/casein. ((do you know a lot about gluten v. wheat tolerance?))
    Thanks
    Katherine

  7. April 22, 2010 5:00 am

    Hey Mae! I am a student at a UC school and I am actually transferring to UC Davis (in!) or Berkeley (9 days till I hear!) specifically to major in Food Sciences. I was wondering, why didnt you apply to either of those schools? They have great programs. As does Cal Poly of course. Just wondering!

    • April 22, 2010 6:39 am

      Hey! Good luck, I hope you get in!! I actually don’t know why I didn’t apply UC… Re: Cal Poly, I was feeling rebellious and my parents had said “absolutely no” to a west coast school, we got in a fight over something unrelated so I went to my computer and researched beautiful places in California, SLO came up, I looked to see if there was a food science program there, and there was so I filled out an application. It was slightly random, but my parents are okay with CA now. I regret not applying to Berkeley or Davis, specifically Berkely because of their enology program. Had I known California was in the realm of possibility, I would’ve thought out the western food science schools more thoroughly. Again, good luck! And I always like “meeting” other food science bloggers. 🙂

  8. April 22, 2010 6:45 am

    HHHMMMM cheese. I do miss thee! Seriously, you are so freakin’ smart. I love food science! Thank you for sharing the info!

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