Kitchen Chemistry – Say Cheese!
Kitchen Chemistry Class
The following is supplementary information, to extend class work and lab work for my culinary students.
But if you are interested in doing some at-home science experiments, to follow is research done for you. The more that kids learn about the foods they put into their bodies, the better! Knowledge equips us to make better choices. Plus, why not get the kids doing more kitchen work, especially when it is so much fun! Seriously, I suffered through a lot of, let’s say “interesting” dishes while my kids were learning to cook… but now they can cook for me! 😀 Method to my madness.
Feel free to use this information at home and be sure to check out the sources at the bottom of the page.
And hey, we do even more cool stuff in the class, so if you can schedule a class, go for it! And I will do the work for you.
First, gotta give a little shout out to my favorite cheese lover… Pixar’s Remi… from Ratatouille, of course. Best movie ever.
What happens when an acid, like lemon juice, is added to heated milk?
What We Will Learn
- The effect of acid on a protein
- The effect of heat on protein
- The chemical reaction which separates curds from whey
- Physical properties of cheese
- Culinary skill: How to make farmer’s cheese and paneer.
Whey: liquid portion of milk containing water, sugar, minerals and proteins.
Curd: solid custard-like state of milk containing protein (casein) and fat.
Aggregate: a whole formed by combining several (typically disparate) elements, clustered together
Coagulation: the process of converting a liquid into a semi-solidmass.
Colloid: a suspension of small particles dispersed in another substance.
Micelle: an aggregate (grouping) of molecules in a colloidal solution.
Chemical reaction: a process that involves rearrangement of the molecular or ionic structure of a substance, as opposed to a change in physical form or a nuclear reaction.
What is milk?
Milk is a colloid; it is mostly water (about 88%) with particles (milk solids) suspending in it, just floating around as happy little micelles and molecules, not connected to each other. These milk solid particles are made up of protein, minerals, sugar, fat, and vitamins.
A Casein Micelle looks something like this. Those little brown lines connecting each tiny submicelle together represent calcium phosphate. This is important.
The parts of the casein molecules that have an affinity for water form the outside of the casein micelle. And the parts of the casein molecule that are repelled by water form the inner core of the micelle spheres. This is what helps these little clumps to stay separate in the water. They just keep repelling each other and floating around.
How do we get those micelles to clump together?
To make cheese, the solids need to clump together, or coagulate. All those little micelles need to stop floating around alone and join up with each other. Each little micelle might be compared to a group of football players huddled together in a field. Now imagine many groups of huddled football players… all clumped up together in one giant mass.
How can we use a chemical reaction to make the huddles of players, micelles, coagulate to form cheese curds?
We can add an ACID! …like vinegar or lemon juice.
There are other methods, as well, like enzymes from the stomach of a goat or cow, but that is another lesson.
When acid is added, chemical changes happen!
- The pH balance of milk lowers. This causes the calcium phosphate (those little brown lines and molecules on the outside) of each tiny micelle to begin to dissolve and form ionized calcium. With the chemistry in the micelle changed, they begin to attract to each other (instead of the water) and they clump together.
- Micelles are negatively charged. Vinegar contains hydrogen which has a positive charge. Opposites attract. This also helps with the clumping.
The micelle changes and gets ready to stick to other micelles to make cheese curds.
When coagulation happens (clumping) milk solids get trapped in the clumps. However, some of them stay in the whey.
The micelles bind together.
It looks like this. Heat is used to speed up the process.
Heat and Protein
When a protein is heated, the protein becomes denatured. It changes chemically from its natural state. All the little folded strands in the protein begin to unfold and then tangle up. Think of it as hair neatly combed and folded into a bun. If you unfold the hair and then twist it and tangle it up, you get a very different… style? Hmm
Tangled hair may not look so pretty, but denatured protein makes meats and bean burgers taste delicious! Think of how high heat browns the outside of a burger. That is delicious denatured protein… called the maillard effect… another lesson.
For curds and whey, we heat up the milk and then add the acid in order to create a quick chemical reaction. The milk proteins, mostly casein, unfold and denature. These curds, unlike the curdled curds from spoiled milk, are safe to eat… if you are lactose tolerant and not vegan.
You could just let the milk sit out and curdle on its own. But I wouldn’t eat it! You will get more than just the milk and vinegar, there will be harmful bacteria as well. Milk has some acidity in it already (lactic acid). If it sits out, it will ferment, the acidity will increase, lowering the pH. The micelles clump. The curds begin the separate from the whey.
Animation created by L2XY2 in collaboration with Dr. Harold McGee
Check out this cool little animation of what happens during the formation of yogurt. Very similar to our experiment. The images above are from this beautiful animation. Image credit goes to L2Molecule.
Dr. Harold McGee is the author of On Food and Cooking: The Science and Lore of the Kitchen.
For some reason, the following video is not working on some mobile devices…
So to see how Milk turns into yogurt, click this link.
In the lab we use this method for Easy Homemede Paneer. Yum!!!
But here is another, very similar method.
Once you have cheese made, smell it, feel it, taste it, study it. How would you describe the texture and flavor?
Click the following link to see all of the easy steps how to form paneer! Easy Homemede Paneer
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Sources – Read More!
- Image and animation credit L2Molecule.
- PBS Learning Media Cheesy Chemistry
- CheeseScience.com Coagulation
- Broadneck.org Milk Chemistry An Introduction
- Food-Info Milk Proteins
- University of Illinois ANSC course studies
- Image (micelle collision) Intro to Rennet
- Idaho Milk Products What is a Casein Micelle?
- Image: University of Guelph Dairy Science
- Cheese Society Milk Coagulants