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the science of steaming milk
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z0mbie
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Posted Sat Oct 12, 2013, 9:03pm
Subject: the science of steaming milk
 

I understand to properly froth milk, you need to first stretch at the surface where air is "sucked" into the milk.  Then you submerge the wand to stop stretching and start heating and texturing, where the existing bubbles get further broken up forming micro foam all the while forming a vortex to distribute the microfoam consistently through the milk (texturing).

But here's what I don't get.  The wand is blowing air the entire time.  It seems counter intuitive that the air being blown into the milk during texturing and heating doesn't just produce more bubbles.  I practice with cold water (with a drop of dish soap) and I can see what's going on under the surface.   Absolutely no air rises to the surface. The water just spins in a whirlpool and slowly heats up with no additional stretching.    Where does all that steam it go?!  By simple logic, one would assume any air blown into the milk under the surface needs to go somewhere. Why doesn't it come to the surface as more foam (given it would be encapsulated in milk or soapy water) in the same fashion of blowing air into a submerged straw. Isn't the same thing happening,  just faster with smaller bubbles?


I tested this again with plain water and still no bubbles come to the surface when heating the water.

Anyone have a scientific explanation for this?
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NobbyR
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Posted Sun Oct 13, 2013, 2:01am
Subject: Re: the science of steaming milk
 

The steam wand doesn't blow air but steam, i.e. water vapor, which condenses when it mixes with the colder liquid. But that's just my two cents worth.

 
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z0mbie
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Posted Sun Oct 13, 2013, 1:11pm
Subject: Re: the science of steaming milk
 

NobbyR Said:

The steam wand doesn't blow air but steam, i.e. water vapor, which condenses when it mixes with the colder liquid. But that's just my two cents worth.

Posted October 13, 2013 link

ah, that makes sense.  When I was heating plain water, I saw no air coming to the surface at all.  In fact I saw no air coming out of the steam wand! The force that was pushing the water was almost invisible.  But still...say I were to blow steam into an empty balloon, it would turn into 100% once cooled?  Wouldn't there be at least some air in the balloon?
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selzoc
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Posted Tue Oct 15, 2013, 8:22am
Subject: Re: the science of steaming milk
 

The air that is sucked into the milk during the stretching phase comes from above the surface of the milk in the pitcher.  You are placing a steam tip opening at the border of the milk and air, and the turbulence created there drives some of the air into the milk.  The air does NOT come from the steam wand in significant quantity to stretch the milk.

When texturing, there's not a significant amount of air entering the milk.
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z0mbie
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Posted Tue Oct 15, 2013, 6:09pm
Subject: Re: the science of steaming milk
 

selzoc Said:

The air that is sucked into the milk during the stretching phase comes from above the surface of the milk in the pitcher.  You are placing a steam tip opening at the border of the milk and air, and the turbulence created there drives some of the air into the milk.  The air does NOT come from the steam wand in significant quantity to stretch the milk.

When texturing, there's not a significant amount of air entering the milk.

Posted October 15, 2013 link

Agreed, but you I think you're answering a different question than what I asked.

I was not wondering where air comes from which froths the milk. Of course it comes from surface. That's what warrants the technique required, which I had described in the very first sentence of this thread..

What I was wondering about is where the air from the steam tip goes.  It does not add any air to the water, nor does it come to the surface. (please review my earlier post).   NobbyR's answer makes the most sense.  But it's fascinating that none of it comes to the surface..
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selzoc
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Posted Wed Oct 16, 2013, 10:20am
Subject: Re: the science of steaming milk
 

Who says that air comes out of the steam tip? :)  It's steam!
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