What controls the heating ability of steamers? Pictured below is a standalone steamer used for foaming and heating milk for milk-based coffee drinks like cappuccinos and lattes. They can be filled with water up to the pressure relief incorporated in the handle which is about 32 US fluid oz (1L) worth.
Once the pressure relief valve starts kicking in, a cup of cold milk can be steamed to about 150°F/65°C in about 60-75 seconds. 
Assuming the steamer is already on the most power gas burner, can:
a) The 60-75 seconds it takes the milk to be steamed to 150°F/65°C be lowed?, and
b) The time it takes the whole process, including initially boiling the water, be lowered?
For example:
a) Would the water level make a difference? 
b) How about the amount of steam let through the wand (controllable by the round knob)?
c) How about the size of the hole at the end of the wand that the steam comes out of? Would more holes or different diameters make a difference?   

 A: This is basically a steam injection heater.
What you have to understand is that to each water temeprature there exists a steam pressure that ou will find (in equilibrium conditions ...) above the surface of the water, and that water will not get hotter if it can boil - if the partial pressure of water vapor is lower than the saturation steam pressure. This is counterintuitive.
There's two ways you can change the heating power, meant here to be the rate at which thermal energy gets deposited into the milk:
I'm assuming that you steam batches of milk - if you operate the steamer continuosly, you will be limitied by the power of your burner.


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*Higher pressure: Don't set the valve to higher pressure, because you will endanger yourself. But if you could do this safely, you could heat the steam to a higher pressure and temperature. This way, you would deposit a greater amount of energy with each volume element of steam.

*Smaller bubbles. This only works if the steam does not deposit all of its energy into the milk allready. But if your setup is somewhat inefficient, or your milk glass very shallow, this might help: You change the setup so that there are smaller holes, then you creqate smaller bubbles and achieve more surface area between the steam and the milk.
