Traditional ricotta cheese is made using whey left over from cheesemaking or drained from yogurt or milk kefir. While not as sweet or creamy as ricotta made using whole milk, traditional ricotta is a wonderful way to utilize whey that might normally be discarded.
2 gallons fresh whey (use within a few hours of straining)
If using both whey and milk, combine the two. Using milk isn't necessary but does substantially increase yield.
Gently heat whey/milk to 195°F. Consider using a double boiler to prevent scorching. Stir constantly and watch the temperature carefully. While it isn't necessary to be exact, be careful not to let the whey boil, as it boils over easily and is very messy.
Remove whey from heat and stir in vinegar. The whey will begin to curdle and some of the curd will rise to the top.
Place a colander in the sink and place a coffee filter or butter muslin in the colander. Gently pour or spoon the mixture into the coffee filter and allow the whey to drain away. Pour carefully, as much of the curd will likely settle on the bottom of the pot.
Once the pot is empty, continue to drain ricotta. One hour is generally sufficient for a soft ricotta. Six or more hours may be needed for a firmer ricotta.