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In the northern-Italian cuisine, ricotta is a favorite component of many Italian desserts, such as cheesecakes and cannoli.
Ricotta is an Italian dairy product made from sheep (or cow, goat, buffalo) milk whey left over from the production of cheese. Sometimes, it's made with additional acid like vinegar or lemon juice.
Although typically referred to as ricotta cheese, ricotta is not properly a cheese because it's not produced by coagulation of casein. This use for the whey has ancient origins and is referred to by Cato the Elder.
Let the whey sit for 12-24 hours at room temperature (just to reach enough acidity).At this step you can add an extra amount of lemon juice.Heat the acidified whey, constantly stirring in it and avoiding burning.
A thin foam will build up. DO NOT BOIL IT.
Remove from heat. Cover the whey and let it stand away till becomes comfortable to touch.
The curd appeared inside the whey, looks like some suspended clouds and the whey should be clear and yellowish-green.
Easily and slowly scoop out the curds.
Drain the whey through a clean wetted cloth (a doubled sheet handkerchief). You need to be patient because the draining process could takes 2-3 hours.
Pick up the corners of the handkerchief then suspend it over the drainage pot and drain the last of the whey . It could takes you several hours.
Store fresh ricotta into refrigerator and consume it in 3-4 days. You also can keep it frozen for a longer period of time.