What is the Smoke Point of Butter?
There is not an easy answer to this one. Typical smoke points are provided in the table below. The smoke point is a straightforward measurement determined by heating the oil until visible smoke appears coming off the surface. It should be emphasized that these values are not absolute but approximations that vary depending on various aspects of the oil and its history. The smokepoint of oil depends to a very large extent on its purity and age at the time of measurement. The smokepoint endpoint varies with aging of the oil, the same oil will deteriorate with time and thus, one cannot be sure of the smokepoint staying the same for the same oil. Clarified butter, is significantly more stable and has a higher smoke point than butter in which there remains 20% milk, but even in clarified butter the smoke point is not constant. The smoke point is variable depending on how it was clarified, how long it has been stored, etc. Clarified butters are typically produced in 'cottage' environments, and the amount of impurities varies a great deal. This means that the quality of preparation has more to do with the temperature at which butter begins to smoke than anything else.
It is recommended to test the clarified butter for its smokepoint and if the method of preparation of the clarified butter is satisfactory for that application, fine; otherwise attempt to purify the butter oil more carefully. Ironically, rendered animal fats especially tallow, traditionally makes the best edible oil on a performance basis, but with the public perception that these fats are inordinately harmful to health, it is difficult to obtain them anymore.
From The New Professional Chef, 6th edition * 1996, by The Culinary Institute of America, published by John Wiley & Sons