First, dilute the citric acid in 1/4 cup cool water. Put milk in a large stainless steel or enamel pot. Do not heat yet. Add the diluted citric acid to the pot and stir to combine. Dilute rennet with 1/8 cup water. Set aside. Over medium heat, bring the milk to 88 degrees F, then turn off heat. Add the rennet solution to pot, folding it in an “up and down motion” for 15 seconds. Then reverse the motion to stop the movement of the liquid. Let milk sit for 5-10 minutes until it’s the texture of silken tofu or a set custard. Cut the curd into large 1 1/2 inch cubes vertically then let curds sit (“heal”) for 2-3 minutes until the whey starts to rise to the surface. Next, very gently cut the curds horizontally by scooping curds one inch down at a time. Work your way through one quarter or half of the pot at a time, shifting the curds from the side of the pot to another until you’ve cut all the curd.
Over the course of 5 -7 minutes, raise the heat to 94 degrees and gently stir the curds. Cut huge curds smaller as you stir. Drain the curds by scooping the curds from the pot with a slotted spoon, into a colander lined with muslin cloth and drain for 20 minutes. Flip halfway through draining.
STRETCHING TECHNIQUE Heat water in a pot to 175-195 degrees. Add salt to taste - it should be very salty - like the sea! Ladle out the hot salted water into a bowl to use for stretching. The water temperature in the bowl should drop to about 165 -185. Manage the temperature by adding more hot water as needed from your pot. Take a small chunk of curd and using a spoon, add it to the bowl with 165-185 degree water. Wait 1 minute and feel the curd and see if it feels softer and more rubbery than before. Try to stretch it gently. If the water is too cold, the cheese will not stretch. If it's too hot it will fall apart. If it stretches, remove from water and tuck and stretch the curd under itself five or six times. Try not to overwork the cheese. Then form a smooth ball by pressing the cheese tightly through your thumb and forefinger (like you're making an "okay" sign), and pinch off the excess curd. Once the mozzarella ball is formed, drop immediately in cold water. Repeat until complete! Enjoy mozzarella within 5 days.