Excellent ricotta cheese can be made on short notice using a sauce pan, colander, supermarket milk, and some fine muslin. Genuine ricotta cheese is a by-product of the production of Parmesan and Romano cheese. It is made from the whey, a cloudy, watery substance that weeps out as the curd is cut and allowed to sit. When making cheese at home it is usual to save the whey for making ricotta. Alas, the yield is usually scant, less than a cup of cheese from the whey left after making a cheese from 2 gallons of milk.
Most books suggest adding additional milk to increase the yield, which works well.
However, it is just as easy to make ricotta from all milk and no whey. This way, you can make it whenever you want and not have to spend a day making other cheese. If the milk is really at 200 degrees, it will instantly curdle, the milk protein and fat separating from the water in smallish white blobs and foam. If this does not happen, keep heating. Use a thermometer, dairy or candy works fine, but some of them are not quite accurate.