The Chemistry of Milk

Milk consists of fats, proteins and sugars.
Milk proteins are critical for milk foaming.
When high pressure steam and air encounter milk, the proteins form a film around the air to create bubbles.

A common question is: "Which is the best milk for steaming for cappuccinos and Lattes? " Simple: Low-fat milk like 2% is almost ideal.

It is the proteins that we are interested in, not the fat in milk. So where the ratio of fat to protein is concerned, obviously, the Low-Fat and Skim milks are of interest to us coffee aficionados.

An obvious benefit here is: Cappuccino and Latte are low in Fat! Start the milk frothing/steaming with fridge-cold milk.

Use a stainless steel carafe and a thermometer capable of accurately reading 140-160 degrees F. Taylor thermometers makes a cute "Cappuccino" thermometer calibrated especially for coffee and espresso fans! Looks good.

Frothing/Steaming milk is a process that is a tad difficult to explain in a text based medium. For that reason, I am going to make every effort to integrate some Video based technology on this page in the very near future.

Start by filling a stainless steel pitcher 1/3 full of cold milk if you are making cappuccino. The amount may be increased to 1/2 full if you are making milk for lattes. Although many people claim that skim, 1%, 2%, or homogenized (whole) milk is best, proper technique is more important.

Equally important is making sure that the milk is well chilled, that is to say, the colder the better.

Figure1: Open the steam valve for a second - pointed into the drip tray - to purge excess water from the line.
Submerge the tip of the steam wand in the milk.
Open the steam valve to release the full steaming power only when the tip of the wand is completely submerged.

Figure 2: Lower the pitcher until the tip of the wand is just below or at the surface of the milk. This is very important.
The tip of the wand should be positioned so that the force of the steam is making a 'dent' in the surface of the milk.
If the wand position is correct you will hear a smooth, but
loud sucking sound as steam/air is blown into the milk.

Figure 3: As the milk volume expands, it will be necessary to correspondingly
lower the milk pitcher, in order to maintain the
position of the wand at the surface.
This is called the stretching phase.

NOTE: This phase will be longer if the pitcher was
filled 1/3 for cappuccino - this is to make more 'foam'.
If the pitcher was filled to 1/2 for latte milk
this phase will be shorter.
After the stretching/frothing phase, which as mentioned,
will be longer for 'cappuccino milk', lower the wand
into the pitcher to finish heating the milk to the desired temperature.

Make certain that you turn the steam valve
off before you remove the wand from the milk.
If you did not stretch (aerate) the milk long enough,
you will hear a jet engine like sound while the tip is submerged.

Professional Tips
If you are using a thermometer, 150F (medium hot) to 165F(hot)
will be the desired range.
Milk starts to scald at 175F and can be seen visually,
by large bubbles forming on the surface.
Professional Barista's seldom use thermometers
but instead rely on the fact that stainless steel
transmits temperature virtually instantly.
For the majority of people, the instant the side of the pitcher
becomes too hot to touch - that is 165F.
This of course can be checked with a thermometer,
but just as easily by taste!

Remember: Always ensure the tip is submerged before
turning the steam valve on and before turning
the steam valve off.

Hot milk splattering can cause burns!

Illustrations C 1991 Nick Zurich, Espresso from Bean to Cup, Missing Link Press, Inc. Seattle, WA 98199 Copyrights © 2002
Text - Colin Newell @ Reg James - espressotec.com All rights reserved