Milk Fat Percentage and Microfoam

[slkinsey]

Ever since I PIDed my Silvia (including the steam temperature) I've had great steam power. But lately I've noticed that the microfoam isn't everything I'd like it to be. In particular, what I find is that the microfoam looks great until I swirl the stretched milk, at which point medium sized bubbles coalesce that are resistant to knocking out. We normally have 2% milk around the house. I've noted that this doesn't seem to be an issue when I use whole milk. Has anyone else noticed this sort of phenomenon?

[Batard]

The fattier milk bubbles in whole milk have a greater surface tension. This gives the bubbles better resistance to bursting or coalescing, the fat stabilizes the foam. I don't understand the science behind it well enough to explain it properly, but it has something to do with the Marangoni effect ...

[gregnz]

This is be the best reference I have been able to find:

http://coffeegeek.com/guides/frothingguide/milk

And the general message regarding fat content (low fat and high fat foams are stable, and there appears to be a trough with whole milk) is consistent with my experience.

Although, it strikes me as odd that they consider skim milk as an option, if we want to "create volumes of foam". This may simply be my bias, but I think the whole endevour is more about texture than "foam". Well textured milk needs no rhetoric in it's defense... it just needs to be experienced!

[barrett]

At certain times of year, as the diets of the milked change, you will need to adjust your steaming technique. I ran into this a couple of weeks ago - the 1% was steaming like styrofoam... or skim. Try less air.

[scubadoo97]

It is all in technique. For good microfoam, don't stretch to long and get a good whirlpool action going while steaming. You should be able to get very silky microfoam from 1 and 2% milk. Good enough for latte art. When the milk has a smooth sheen that reminds me of marshmallow cream I know I've done it right.