building a better pantry: homemade mozzarella

Just like homemade butter or ricotta, homemade mozzarella will change how you view this mild, un-aged cheese.
If you've ever had a mozzarella-tomato salad (also known as insalata carprese) made with really good mozzarella, you know that what they (whoever "they" are) put on pizza is a shadow of mozzarella. Mozzarella lite, if you will.
As with all cheeses, making mozzarella is like magic. In a feat of culinary transformation, a humble gallon of milk becomes a smooth, lightly tangy, stretchy, thoroughly meltable cheese.
There are several good mozzarella recipes out there. Mine is based on Ricki Carroll's from Home Cheese Making. She has a 30-minute mozzarella recipe as well, which I hear good things about. I haven't tried it because I infinitely prefer the flavor that live cultures give to the final product over citric acid. What's more, I believe that high-quality cheese demands patience. There's nothing difficult about it, but you need to be able to wait.
Let's discuss bacteria cultures. Buying live cheesemaking cultures can be a little daunting, but there's really nothing to it. For basic cheesemaking, two cultures are needed: mesophilic and thermophilic. If you can reach back in your memory to biology class, you might recognize these words. Mesophilic cultures are composed of bacteria that thrive in moderate temperatures (between 80°F and 110°F). Thermophilic bacteria thrive in higher temperatures (as high as 132°F).
There are other cultures out there. Lots of them. But for now, what you need to know is that the basic two are mesophilic and thermophilic. For mozzarella, you'll use a thermophilic culture.
I like to use lipase in my mozzarella. Lipase simply gives a stronger flavor to many Italian cheeses, such as mozzarella. It is made of the pre-gastric glands at the base of an animal's tongue (calves, kids, or lambs more specifically), which are dried and ground into a powder. This is not a vegetarian additive, so feel free to leave it out. It's not necessary to include lipase in your cheeses. It simply results in a more flavorful end product.
Finally, you'll need to track down rennet. Rennet can be found in tablet or liquid form, and you can find either vegetarian or non-vegetarian rennet. I use the liquid form, which is available at some health food stores (I've seen it at my local coop) or online. Some critics of vegetarian rennet say that, in time, it gives cheeses an off-flavor. For un-aged cheeses like mozzarella, however, this is not an issue, so vegetarian rennet will be just fine.
For those of you who are a little daunted by the idea of having to find and purchase bacteria cultures, there are methods of making mozzarella that use citric acid. Food52 has a great one, and it will serve you in good stead.
The reason I like to use powdered culture is, again, because I feel it gives the final product more flavor and produces a more authentic cheese. But then again, after apprenticing with a cheese maker, I know that using powdered cultures is no big deal, and for a packet of mesophilic culture that contains enough to culture 250 gallons of milk, you'll pay just over $10. Not a bad deal if you plan on making cheese more than a few times.

Homemade Mozzarella
Adapted from Ricki Carroll's recipe in Home Cheese Making
makes about 1 pound of cheese

Heat:
            1 gallon fresh milk
to 90°F in a large saucepan. I advise using whole milk for a higher yield. You can use goat's milk, in which case you will not need the lipase.
Turn off the heat and add:
            1/8 teaspoon thermophilic starter culture
            (1/8 teaspoon lipase powder, dissolved in 2 tablespoons cold water)
Stir well, using a rubber spatula in a top-to-bottom motion to thoroughly distribute the culture. Cover the milk and let ripen for 30 minutes.
Add:
            4 drops liquid rennet, dissolved in 2 tablespoons cold water
Stir, again using the top-to-bottom motion. Cover again and let the milk coagulate for about an hour to an hour and fifteen minutes.
To test the curd, there are multiple methods. Over time, you'll develop a feel for when the curd is ready. My favorite is to use the back of your hand to gently press down on the curd mass at the edge of the pan, where the milk and the pan meet. If the curd is ready, it will pull away from the sides of the pan without breaking.
Using a sharp knife or an offset spatula (such as the ones used for spreading frosting on cakes), cut the curd into 1/4-inch cubes. Do this by cutting the curd mass into thin strips in one direction, then cut into thin strips in the opposite direction (cut perpendicular to your first cuts). At this point, your curds are in the shape of really long rectangles, stretching from the top to the bottom of the pan, so you'll want to cut them again, this time diagonally. This is a difficult step to explain, so my advice is to cut the curds as close to the right size as you can, and then later, when you stir the curd, break up any larger curds as you go.
Let the curd sit, covered, for 15 minutes.
This resting process allows the curds to firm up slightly so they aren't quite as fragile.
Heat the curds to 100°F. You'll want to do this slowly, so use the medium-low setting on your stovetop. Stir constantly. Once the curds have reached 100°F, turn off the heat and let rest, covered, for 5 minutes.
Drain the whey from the curds. You can save it for another use (making ricotta, making whey-based drinks, making lacto-fermented pickles, or for giving to your chickens) or simply pour it down the drain.
Fill your sink with 102°F water, and set the pot of curds in the water. Every 20 minutes for 2 1/2 hours, drain off the whey and flip the curds over. This is not set in stone--I fell asleep during this process once, and everything was fine. The general idea is that you want to keep the curds warm (thus the water bath), drain off whey, and give the curds plenty of time to acidify.
After 2 1/2 hours, tear the curd mass into small pieces about the size of quarters. Place half these curds in a bowl of 170°F water, and, with gloved hands (I just use dishwashing gloves that I reserve for mozzarella making only), knead the curds. Eventually, and in my experience this doesn't take very long, the curds will knit together into one mass--this can take anywhere from 5 to 20 minutes.
Work the curd mass with your fingers until it becomes smooth and shiny. At this point, you should be able to pull the cheese like taffy. Repeat this process with the remaining curds.
You will now have two smooth balls of mozzarella.
Combine in a medium bowl:
            1 pound kosher salt
            1/2 gallon cold water
Place the mozzarella in the cold water to firm it up and salt it. This takes about one hour. At this point, the cheese may be eaten fresh or refrigerated for up to one week. I have also had great success freezing this cheese. In fact, if you would like to grate it, it's much easier to do if the cheese is partially frozen.