Making your own mozzarella takes some time, and it may take a few tries to get the results you ultimately want, there is nothing like fresh cheese using great milk. I promise you will get hooked on this!
1⅛ tsp. citric acid
¾ cup cool un-chlorinated water
1 gallon good quality, local, low-temp pasteurized (not ultra-pasteurized) milk
¼ tsp. liquid rennet
Pour milk into a heavy bottomed pan and begin to heat over low heat.
Dissolve citric acid in ½ cup of water. Stir vigorously to dissolve (this can take about a minute). When completely dissolved and milk is around 50 degrees, stir into milk mixture.
Continuing over low heat, heat milk mixture to 90 degrees. Cut the heat and reheat if the temperature starts to drop. Try to keep the temperature around 90 degrees at all times. Mixture will start curdling - but it may not be very much.
Keep at this temperature, stirring occasionally for 1 hour.
Stir rennet into remaining ¼ cup of water.
Using straining spoon pour rennet mixture over milk and use spoon to mix in using an up and down motion - 10 to 12 times. Cover and let stand for 15 minutes.
At this point, mixture should be solid and will look a lot like tofu. Using a knife, cut mixture into 1 inch squares. Cover again and let stand for 10 minutes.
Keeping temperature around 90 degrees, lift and turn curds every 10 minutes three times. Then allow to stand for 30 minutes covered and undisturbed. Again you should check the temperature and add heat when necessary.
Line a colander with a double layer of cheesecloth and set over a bowl. Using a large slotted spoon to lift cuds into cheesecloth. Pull sides of cheesecloth together and tie tightly with a long piece of string. Do not squeeze the curds.
Hang curds from a cabinet knob with a bowl underneath to catch the whey. Leave for 3 hours. Reserve some of the liquid to store the cheese.
Heat large pot of water to 180 degrees. Cut curd out of the cloth and cut into quarters. Then cut each quarter into strips. Gather curds into large slotted spoon and lower into water. Allow to sit in water until cheese starts to meld together (could be 2 or 3 minutes).
Lift cheese out and working over a bowl with rubber gloves, sprinkle with salt if desired and stretch and fold cheese over until it becomes shiny, smooth, and elastic. If the cheese starts to cool down too much put it back into the water and allow to meld together again. Then rework it only as much as is necessary - fold into a ball and pinch edges together.
Cool in ice water for 10 to 15 minutes.
Store cheese in strained whey. Refrigerate. Mozzarella will keep for up to 4 days.