Is there some way to narrow down the Leidenfrost point for water? Cooks sometimes use the Leidenfrost effect to estimate the temperature of a frying pan by flicking a few drops of water onto the heated pan. I had no idea, before looking into this, that this could be such a rough estimate.
One site I looked at has the Leidenfrost point for water at  482°F (250ºC).
The Wikipedia article (without citation) places the temperature that this happens around 193ºC, but also notes that the estimate is quite rough,

The temperature at which the Leidenfrost effect begins to occur is not
  easy to predict. Even if the volume of the drop of liquid stays the
  same, the Leidenfrost point may be quite different, with a complicated
  dependence on the properties of the surface, as well as any impurities
  in the liquid [...] As a very rough estimate, the Leidenfrost point for
  a drop of water on a frying pan might occur at 193 °C (379 °F)

When estimates differ by more than 50ºC, that really is pretty rough (from a cooks perspective at least).
My first question is whether it is correct that the Leidenfrost point for water really is so difficult to pin down?
And secondly, is there anything cooks can reasonably do to improve this technique in terms of recipe repeatability?
 A: I'm not that much of a science guy, but I'm thinking it would be real difficult for a cook to pin that temperature down. There are just too many variables I can think of that would influence when the Leidenfrost effect would start to occur and how long the droplet will last.  


*

*Temperature of the pan.  

*Surface texture of the pan.  

*Material of the pan (thermal conductivity wise).  

*Temperature of the droplet.  

*Density of the droplet.  

*Amount of liquid in the droplet.    

*Properties of the droplet (thermal conductivity wise).  

*Atmospheric pressure.  

*Velocity at which the droplet is thrown in.  

*Angle at which the droplet is thrown in.


And these are just the ones I'm thinking of, not to mention if I actually was a science guy.
If I could try to give your questions an answer, I would have to say that the temperature of the heated pan at which the Leidenfrost effect would begin to occur could be pinned down exactly if every other variable was fixed. For cooks this would be rather difficult.  
But to narrow the range down a bit for home cooking use, you could get a pipette which produces an consistent droplet, and drop it at a set height from the pan. And, of course, keep using the same frying pan (also keeping its surface undamaged). As a consistent droplet source you could use bottled water. This will not tell you the temperature of your frying pan but can be used as an indicator when the temperature reaches a certain point.
A: As a 12 year chef, yes we do--if you put your hamburger in a cold pan and raise the temp you are not browning your meat, you are graying it. The pan has to hit a temp that it will immediately vaporize any water on the outside of the meat so the meat itself can make contact with the pan and sear, thus browning. To find out whether or not the pan is hot enough to instantly vaporize the water on the meat, get our fingers wet and sling the water droplets off of our fingers. If the leidenfrost effect triggers it is hot enough to brown meat, if it does not it is not and you are graying your meat. If you do not sear the outside of the meat, then the meat will continually loose moisture to the pan that the pan cannot heat up high enough to get rid of, as the temperature of the pan cannot go above 212 while there is water in the pan--all extra energy goes into breaking the hydrogen oxygen bonds, and the suboptimal heat keeps causing your meat to leak--if there is no excess water in the pan the meat sears at around 400-500 the entire time and the meat's chill will help modulate the pan temp so as to not be too high. It puts out a bit more smoke but results in a significantly juicier, more flavorful product in whatever you're making, to brown the hamburger and not gray it (you, reader, probably do not have the pan a high enough temp when you start, and you, reader, probably are graying your meat.) Increase the temp of your pan before you add your taco meat, and all you will drain will be fat, not 3/4 water, and it will taste miles better. You're welcome, trigger leidenfrost before you add your meat, always, unless you're specifically making a Blanco (white) Stew, in which case you want gray meat to not see it.
Source--culinary arts degree and 12 years in the field, answering a specific question of the poster with real world experience his question asks for.
