Simple Home Cheese Making and its Science

My first cheese making experience was completely accidental.  As a child, I was in the kitchen and happened to have both milk and vinegar within reach; naturally, they got mixed together.  I noticed a near instantaneous curdling, though it wasn’t until some years later I really grasped what I had done- I had made cheese.  Relatively recently, even after knowing some of the basics of cheese making, I again fell victim to accidental cheesery: I mixed some milk into a tomato based dish as it simmered and was surprised by the resulting simple cheese in my dish (it turned out to be quite good- I do it on purpose now).  There are many simple fresh cheeses that anyone can make at home.  They make for a great compliment to snacks and meals, and are a fun weekend science project to do with kids (or in my case, my inner child).

These simple cheeses, unlike their aged cousins like cheddar or brie, are not actually fermented (and so don’t fit perfectly within the scope of this blog, but oh well).  They simply have some coagulant added to separate the the milk into curd and whey.  Curd is the solids of the milk- proteins (most importantly casein), fats, salts, and some moisture.  Whey, the part of milk which does not become cheese, is mostly water, but also contains some lactose and other non-coagulating protein.  More on the science later- for now, lets get to making some cheese.

For this simple cheese making, the product known as milk in the refrigerator section of just about any supermarket- pasteurized and homogenized- will work.  However, you must avoid ultra-pasteurized milk.  This has been heated to a higher temperature which is capable of denaturing (disabling) the all important proteins in the milk.  It is rare to find ultra-pasteurized milk, so you shouldn’t have to worry too much, although finding heavy cream which has NOT been ultra-pasteurized is nearly impossible.  Also, in all recipes when using pasteurized milk, it might help to add about 1/2 tsp/ 2.5 mL of calcium chloride powder if you find the curds are not forming well.  The pasteurization process destabilizes some of the calcium compounds present in the milk and adding more back can help to firm the curd and hasten curdling.  If so, add it to the milk while it is still cool.

Some Recipes

Queso Blanco
This is about as simple as cheese making gets, and there’s a good chance you have everything to make it in your house right now.  It will not completely melt when heated, so use it in a dish where you want cheese relatively well distributed, but with some small chunks left over.

• 1 gal/ 3.8 L milk
• about 1/3 cup/ 80 mL distilled or cider vinegar
• 1 tsp/ 6 g fine salt
• butter muslin (optional, but nice to have)
• calcium chloride optional

1. slowly heat milk to 195F/ 90.5C over about 30 min, stirring to prevent scorching
2. stir in vinegar with whisk; let sit for 10 min; if the whey remains very cloudy, add additional vinegar 1 tsp/ 5 mL at a time and stir gently until whey clears
3. line a fine strainer with butter muslin if available; gently ladle or pour curds through strainer and drain for 5 min
4. hand toss salt into curds
5. drain until dripping stops, about 1 hour
6. use within 24 hours for best results, or store in airtight container refrigerated for up to one week

Panir
This is a firm Indian farmer’s cheese, used perhaps most famously in saag panir.  It is also great for any dish requiring frying or grilling, as it is will hold its shape under high heat and brown up nicely.  Feel free to scale it up to use the full gallon of milk (or whatever volume its sold in near you).  The buttermilk is used only for acidity, so it need not have a live culture.

• 2.5 qrt/ 2.4 L milk
• 5 cups/ 1.2 L buttermilk
• 1/2 tsp/ 3 g fine salt
• butter muslin (optional, but nice to have)
• calcium chloride optional

1. bring milk slowly to 175-180F/ 80-82C over about 40 min; turn off heat
2. pour in buttermilk and stir gently to just combine; coagulation should occur immediately with curds forming in about 2 min
3. slowly raise the temperature to 195F/ 90.5C; this temperature controls how firm the cheese will be (higher =  more firm)
4. turn off heat and stir gently for about 10 min until most curds have formed into one mass
5. carefully dump through a fine strainer to get rid of the whey (or you can save it for other recipes); if you have some, line first with butter muslin for better results
6. let drain for 10 min, salt and toss the curds with your hands, and drain until they stop dripping (about 10 min); you can add spices with the salt (ie 1 tsp cumin) if desired
7. form the curds into a brick shape about 1″/ 2.5 cm thick; here it really helps to have some butter muslin to tightly wrap the brick
8. put on a drying rack and weigh down with something clean and about 4 lb/ 1.8 kg (a plate with a jug of water on top for example); let drain for 30 min, or more for a drier cheese
9. the cheese should now be a solid brick; cut and use fresh or tightly wrap in plastic and store refrigerated for up to 4 days

Simple Mozzarella
This is about the most simple way to make mozzarella I have found, but it will require rennet, which you probably don’t have laying around.  There are other, more complex versions that actually do use a culture to add flavor, but I find this version to be quite enjoyable in a tomato basil salad or on pizza.  Austin Homebrew Supply has a great cheap kit with all the ingredients, as well as some other websites.

• 1 gallon/ 3.8 L milk
• 2 tsp/ 10 mL citric acid powder in 1/4 cup/ 60 mL water or 1/3 cup/ 80 mL lemon juice
• 1/2 tablet rennet or 1/4 tsp/ 1.2 mL liquid rennet in 1/4 cup water
• 1 tsp/ 6 g fine salt
• calcium chloride (optional, but recommended)

1. pour acid into milk and stir, then heat to 88F/ 31C slowly
2. remove from heat, add rennet and stir in up-and-down motion for about 1 min; if you accidentally overheated, let it cool back to 88F before adding
3. heat to 105F/ 40.5C, remove from heat, and cover (this temperature will help determine firmness of curd)
4. after 20 min undisturbed (more if whey is still cloudy), run through strainer to separate curds from whey
5. move to microwave safe bowl, microwave for 1 min
6. knead the curds until they cool, adding salt and draining excess whey (you may want rubber gloves for this step, especially for kids- it can get hot)
7. microwave for 30 sec and knead further; repeat until smooth and elastic- the more this is done, the smoother and more firm the cheese will be
8. eat warm or cool in an ice water bath

The Science

And now, because I can’t resist, a short primer on the science of basic cheese making.  There are two important groups of proteins in milk- those that make up the curd, and those that remain in the whey.  These proteins are enormously complex large (relatively speaking) molecules, as seen in the atomic model image below (click to enlarge).  Those that make up the curd- the casein family (there are four types of casein in milk)- are important to cheese making.  In milk, calcium ions are responsible for binding individual casein proteins into clusters of 15 to 25.  Calcium ions and hydrophobic (water hating) portions of the proteins then cause these clusters to bind together in groups of several hundred clusters (hydrophobic molecules hate to be next to water, but like to be next to each other).  One of the four casein proteins, kappa-casein, forms a sort of capping layer on the group once it reaches a certain size, preventing the group from getting any larger, which is why milk doesn’t spontaneously form into cheese.

Atomic model of kappa-casein protein. Click to enlarge.  Left: the negatively charged tail is clearly visible on the right; Right: same image rotated slightly to show more structure, tail still visible to the right. Grey = carbon, blue = nitrogen, red = oxygen, white = hydrogen, yellow = sulfur, orange = phosphorus

The kappa-casein prevents larger groups from forming because it has a negatively charged end which sticks out as shown in the image above; like charges repel like magnets turned the wrong way, keeping the groups from getting close.  So, the first thing that must be done in cheese making is to somehow get rid of this negative charge on the casein protein so they will come together to form a curd.  In general, there are two ways of making this happen: the milk can be acidified to neutralize the negative charge, or the protein itself can be attacked with an enzyme.

Acids, by definition, have an abundance of positively charged hydrogen (H⁺) ions compared to the amount of negatively charged hydroxide (OH^–) ions; bases are the opposite.  So, with the addition of acid to milk, there are more positively charged ions in solution.  As the milk becomes more acidic than its usual pH of about 6.5 (just slightly acidic; 7 is neutral on the 1-14 scale), a number of things begin to happen.  At a pH of about 5.5 (its a logarithmic scale, so there are now 10 times more H⁺ ions than before), the H⁺ ions neutralize the charge on the kappa-casein and allow the groups to come together.  Simultaneously, the calcium can no longer hold the proteins in their small clusters and the proteins are released.  As the milk becomes even more acidic, the negatively charged portion of the individual casein proteins are neutralized and the proteins bind to each other in a large continuous network, trapping fat globules and other components of the curd.

There are two ways of acidifying milk: direct acidification as in the recipes above, or fermentation by lactic acid producing bacteria such as those in the Lactococcus and Lactobacillus genera, which are also important in many sour beer styles, sourdough bread, and other products.  Direct acidification can be achieved by simply adding any number of acids to cheese- lemon juice (or pure citric acid from your local homebrew supply), cream of tartar (tartaric acid), lactic (like in buttermilk), acetic (vinegar), malic (found in many fruits), or others.

The other option to allow curd formation is with rennet.  Rennet is the enzyme rennin, also called chymosin.  Historically, rennin was sourced from the stomach of kids (the goat),  lambs, or most frequently calves.  Today, many vegetarian options exist: it can be sourced from various plants or especially the mold Rhizomucor miehei.  Enzymes are molecules which attack and break down proteins.  Generally they are very specific and only work on certain proteins.  In the case of rennin, not only does it work only on casein, but it will only snip off the negatively charged portion of the protein.  Thus, the casein can coagulate into a curd without the usual accompanying acidity.

Frequently, both rennet and acid is used.  Curds formed by acidulation are much softer and more fragile, almost gelatinous, and have some tartness.  Conversely, rennet forms a firm rubbery curd.  By using a combination of the two methods, one can control the texture, firmness, and flavor of the cheese.

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Most of the information for the science section comes from McGee’s On Food and Cooking and Karlin’s Artisan Cheese Making at Home.  Two of the above recipes are also from Karlin’s book- I highly recommend getting it if you find you enjoy cheese making.  The protein atomic data was originally published in Three-Dimensional Molecular Modeling of Bovine Caseins: A Refined, Energy-Minimized Kappa-Casein Structure (1993) Journal of Dairy Science, now available online at http://www.arserrc.gov/CaseinModels/ with .pdb model files and displayed in Mathematica as a ball-and-stick model. [2014.06.12 UPDATE: This link has been broken for a while- I think since the government shutdown.  Maybe it will eventually be back?  2014.09.05 UPDATE: You can see the original article here, but the .pdb model files I used are lost to the broken link.]

– Dennis,
Life, Fermented

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