Top Down for Great Milk Foaming
Making great foam for cappuccinos isn't rocket science, although you might think that when you see the varying quality dispensed at various food service outlets. A little understanding of what makes milk foam helps at this point.
Cows milk is full of fat and protein and it is this combination that allows the Barista to foam the milk. The problem is that if you don't make any attempt to foam the milk prior to simply heating it, the fats and protein will all melt away and it is impossible to foam anything.
Knowing the above now leads to an understanding as to why milk should always first be "stretched" to create foam prior to heating the milk. Then then leads me on to the top down theory. That is, when wanting to foam milk, the steam wand should be placed at the surface of the milk to ensure that steam and air are driven into the milk. Tilting the milk pitcher and angling the steam wand should ensure that you get a vortex effect in you milk.
Once you've created sufficient foam, you can if necessary heat the milk further by lowering the wand into the liquid. Take care not to overdo it. So top down it is.