Pour the milk into a large pot and set it over medium heat. Let it warm gradually to 200°F, monitoring the temperature with an instant-read thermometer. The milk will get foamy and start to steam; remove it from the heat if it starts to boil. Don’t let it boil!
Remove the milk from heat. Pour in the acid (lemon juice or vinegar) and the salt. Stir gently to combine.
Let the pot of milk sit undisturbed for 10 minutes. The milk should have started to separate into clumps of milky white curds and thin, watery, yellow-coloured whey — use a spoon to check the mix. If you still see a lot of un-separated milk, add another tablespoon of lemon juice or vinegar and wait a few more minutes.
Set a strainer over a bowl and line the strainer with cheesecloth. Pour the liquid and curds through the strainer.
Let the ricotta drain for 10 to 60 minutes, depending on how wet or dry you prefer your ricotta.
Fresh ricotta can be used right away or refrigerated in an airtight container for up to a week.
