Mix salt into a bowl(3-4 qt) of ice water to make brine (used to cool finished cheese), set aside
Pour milk into 6qt or larger stock pot
Dissolve citric acid crystals in 1⁄2 cup cool water; add acid solution on to the cold milk, stir thoroughly
Gradually heat the milk to 90F; stir occasionally to heat evenly
Dissolve ~12 drops rennet in 1⁄2 cup cool water
Take the milk off the heat and thoroughly stir in rennet solution
Let milk sit undisturbed for 20 minutes or until the curd sets and breaks cleanly
Use a long knife to cut the curds into 1 inch by 1 inch squares
Place stockpot with the curds back onto stove and very gently stir the curds as you heat to 130-140F. The curds will become stretchy and stick together when they are ready(it will look like slightly melted cheese)
Using a slotted spoon, remove a fist-sized ball of curd from the whey. Using gloves to avoid burning your hands, stretch and work the curd for 5-10 seconds. The more you work the curd, the more dense/rubbery the final product
Submerse the mozzarella in the brine to cool for 10-15 minutes. Mozzarella will last for up to a week in the fridge if stored in the brine