In a bowl, mix the citric acid and water and stir until dissolved.
Meanwhile, in aseparate bowl, mix the rennet and water and stir well until dissolved.
Pour the milk into a large pot and add the citric acid mix. Warm the mixture over medium heat and stir slowly but constantly until the milk reaches 32ºC/90ºF. Remove from the heat as soon as you reach the required temperature.
Add the rennet mixture to the warm milk and stir a few times slowly to mix well. Then cover the pot and set aside for 5 minutes.*
After about 5 minutes, the milk should have 'set' and be a consistency similar to a thick yogurt or pudding that you can slice through. If you can cut through it nicely in a straight line, you can move to the next step. If not, set aside for another 5 minutes and try again.
Stage 2 - Prepare the curds
To cut the curds, It's best to create a grid pattern through the curds, first slicing one way, then the other. Make sure to cut deep into the cuts, by touching the bottom of the pot.
Then, heat the curds over medium heat and stir very slowly but constantly. Try not to break the curds too much. They only need to reach 41ºC/106ºF so they will warm up quite quickly (this heating will help the curds to toughen slightly).Remove the pot from the heat as soon as the required temperature is reached. Continue to stir, slowly, for another 5 minutes. During this time, the curds will begin to separate from the whey.
Scoop the cheese curds from the pot with a slotted spoon, into a large colander lined with cheesecloth/muslin or a nut milk bag and allow the curds to drain into a bowl (as this whey can be used) for around 5 minutes.
You can either set the whey aside now or use around half of it for the next step.
Stage 3 - Shaping the mozzarella
Fill up a large bowl with hot water or heat up the whey liquid** (until about 76ºC/170ºF) and place the curds inside. It may be easier to divide the curds in half and do this in two go's.Keep the curds in the hot liquid for a few minutes. This is when the mozzarella is taking shape - the curds should become stretchy, a bit smooshy, and look a little like melted cheese***.
Finally, remove from the hot whey/ water, add some salt and then stretch and fold the curds onto themselves (using gloves), like how you would with taffy. Repeat until they become shiny and firm (usually just a few folds will do like between 3-7- don't overwork it). Then roll into balls and quickly cool them. (See in the video).If it's hard to shape into a ball or comes apart while stretching, place back in the hot liquid and allow to heat up a little more to shape into the final, smooth ball. You can also make small mozzarella balls (Bocconcini).
How To Store
Serve the fresh mozzarella immediately or store in the fridge in the whey or a slated brine for up to a week.You can also freeze the mozzarella for up to six months.
* Tip: If you can, stir in an up and down motion rather than swirling. The quicker the milk becomes motionless after the rennet is added and mixed in, the better as otherwise, it may not set correctly if it's still whirling away. I aim for 15 seconds maximum of mixing.** Using whey instead of water and add a little extra flavor to the cheese.*** You can also use a thermometer to check when the curds are ready to stretch. You're looking for an internal temperature of 135F in the cheese.
If you use goats milk instead of cows then be even slower and gentler when stirring the milk, so as not to disturb the curds too much.
If your cheese is tough or crumbly then this is likely down to using too much acidity or heating it incorrectly. However, it can also happen if the curds are broken up too much by rough mixing. Try to reduce the amount of citric acid in the next batch.
If the cheese is rubbery then it's likely that you overworked it during the stretching phase.
For a softer mozzarella, stop the curds from becoming as firm and work the cheese even less when stretching (literally just a couple of stretches).
You could add some dried herbs to the cheese, if wanted, during the final shaping stage.
TOP TIP: A 'failed' batch definitely doesn't necessarily mean waste. Even if the cheese is crumbly and won't stretch, this can be used within pasta dishes, into cooked dishes, etc.