Steaming milk is also an important step in overall coffee preparation and it can make or break a great coffee. The milk should have a silky velvety texture, have natural sweetness bought on by caramelisation and be the perfect temperature. There are many different techniques for processing milk so find one that works for you.
Here's mine -
There are two distinct processes involved in milk preparation - 1. Stretching the milk. 2. Heating it to the desired temperature.
1. Stretching introduces air into the milk, via the steam wand, to increase its volume. This process should start when the milk is cold and finish when the milk is about 40 c. Don't stretch the milk beyond this temperature, it will lead to large bubbles and excess foam.
2. The second phase is to heat the milk to the desired temperature, between 60 and 70 C, and to create the velvety texture.
Start with a cold jug and some cold milk, only fill the jug with the amount of milk that you need to use. Purge the steam wand to get rid of condensation. Pull out the steam wand at an angle so the wand tip points to the 9 o'clock position.
Place the steam wand into the jug resting it on the jug spout, hold the jug at an angle but make sure you can still see into it. Place the wand tip, still in the 9 o'clock position, just below the surface of the milk and about a 1cm away from the side.
With the tip about 1cm into the milk turn on your steam wand progressively, the idea is to immediately start the milk spinning inside the jug, like a whirlpool. As soon as the milk begins to spin lower the jug very slightly until you hear a minor hissing sound. The sound should be minor and should come and go, if it's loud and continuous you have lowered the jug too far and are introducing too much air into the milk.
Keep stretching the milk, about 5 seconds for Cappuccino, 4 for Latte etc. As the volume of the milk increases you may need to slightly lower the jug to continue stretching. Each machine has different steam pressures so experiment and don't forget it's also about personnel preference.
Once the stretching phase has finished raise the jug very slightly to return the steam tip into the milk. Place your hand on the side or base of the jug to feel its temperature. Keep the milk spinning - this will create the velvety texture.
If you have a temperature gauge turn the steam wand off approx 5 - 10 deg C before the desired temperature is reached as the temperature will continue to rise. If you are using your hand to judge temperature then for the average person the milk will be ready when you can no longer hold your hand against the jug. Bear in mind that heat tolerances are different for every person, so adjust accordingly, as an example you may have to remove your hand and count to three before the milk reaches temperature.
Do not heat the milk more than 70 C as it will overheat, it will lose its natural sweetness and smell eggy. The ideal milk temperature is between 60 and 70 degrees C.
Wipe the steam wand with a damp cloth and purge it. If you have any large bubbles in your milk bang the jug onto the table to remove them. Do not allow your jug to sit on the table with the milk stationary as the textured milk will separate. Keep rotating the jug in circular motions, spinning the milk, until you are ready to pour. Pour your milk as soon as you can into your prepared espresso shot. Tilt the cup and pour evenly, into the centre, until full.