How to Froth Milk
Frothing milk correctly is the 2nd most important thing you need to know after learning how to make the perfect espresso. When frothing (sometimes called foaming) or steaming milk for coffee, it is very important not to overheat it. As milk boils it releases sugars which totally change the flavour of the milk and ultimately the coffee you are making. Also if your coffee is too hot the first thing your customer will do is burn his/her tongue and that will stay with them for the rest of the day, not the best way to encourage repeat business!
The milk should ideally be 65 - 70°C, (above 70°C sugars start to be released), You can get thermometers to help you achieve this, some even have this temperature range marked in red. When relying on a thermometer reading remember the temperature may rise slightly after turning the steam valve off. Your hand is also a good guide, place a hand on the bottom of the jug whilst heating the milk, when it becomes too hot to hold that is the point to turn the steam arm off. Also, never try to re-froth milk without adding at least half as much again in fresh milk. Even better, try and learn how much milk you need for a particular drink so that you dont get left with much in the frothing jug between making drinks.
It is also important to note the difference between 1) frothing/foaming milk for drinks such as cappuccino where a good amount of foam is required as this forms a large part of the drink, and 2) steaming milk for drinks such as latte which requires only a small amount of foam to decorate the top of the drink.
Foaming/Frothing Milk
Keep the nozzle towards the top of the milk to start with, this gets more air into the milk to make it expand. You don’t want it blowing loads of large bubbles into the milk, you will be able to tell if its too close to the top of the milk as it will make quite a lot of noise. In this case put the nozzle slightly lower, typically it might be about 1-2cm below the surface, but this will vary depending on what type of steam arm you have, how much pressure it produces and what type of milk you are using. As the milk stretches lower the jug so that the nozzle stays 1-2cm below the surface. Once the milk has stretched to about double its original size, if the correct temperature hasn’t yet been reached move the nozzle to the bottom of the jug until the correct temperate is achieved.
Next, tap the jug on a work surface several times to break up any large bubbles, and swirl the jug in a circular motion on the counter. After a while it should appear shiny, this means its ready to pour. When foaming never fill the jug more than about a third full of cold milk as it can expand by up to 3 times.
Steaming Milk
This is not so frothy. Keep the nozzle at the top of the milk for only a short while then move it to the bottom of the milk until the 65 - 70°C temperature is reached. In reality most people have to make a mixture of cappuccinos and lattes so they tend to just make foamed milk and use a spatula/knife to hold the foam back for lattes.