In a large (7- to 8-quart) heavy pot, combine the whole milk, buttermilk and lime juice. Heat the mixture over medium until a cooking thermometer reads 190 degrees. This will take about 20 minutes. The curds will begin to separate from the whey and float to the top of the pot.
With a slotted spoon or wire skimmer, gently skim the warm curds from the top of the whey and place them in a medium mesh strainer lined with cheesecloth. Let the curds drain from the whey for about a half hour, until the desired consistency is reached. Chill the ricotta until you’re ready to serve.