Milk + banana - why did it almost look like whipped cream?
today, I tried to make a simple banana ice cream, by simply smashing a bunch of frozen banana slices in my food processor. It didn't work very well (maybe the banana pieces were to cold, so the knives were unable to cut properly through them), so I figured I'd make it easier for the food processor if I added some milk. Don't know if the reasoning was correct, but anyway, I poured in some milk (0,7% fat), let the food processor work some more, and, to my amazement, the milk started to behave almost like whipped cream. Not quite as stiff, and also not as stable, but still very cream-like.
Afterwards, just to check, I ran the food processor with just some milk, and as expected, nothing special happened.
So, some stuff in the banana must have given the milk a much better ability to maintain a foam. Does anyone have any idea what was at work here? Was it the banana sugar? Or does the banana have some lecithin or lecithin-like foam-stabilizing proteins? And to other fruits/other common ingredients also have this ability to make milk foam?
Maybe the fat in the banana did something? Also, pureed banana is so creamy anyway, maybe the milk just thinned it out some and it ended up looking like whipped cream? (You could try repeating the experiment but with water/juice/soy milk instead to see if it gives you a similar result.)
My guess is that since the banana was frozen, its coldness is what made the milk foam by solidifying the little amount of fat in the milk.
I often make faux ice cream using frozen bananas. Defrost them, then while still cold puree them along with other fruits, cooled melted chocolate, other flavorings, and sometimes a little dairy. Then refreeze right away. The less fatty it is, the harder it will freeze, unless you use guar gum. But even without, it will not be rock-hard, and remains scoopable if you use a heated scoop, or nuke the container for 10 seconds. Thawed bananas are pulpy and release a lot of liquid. I am not sure if the "ice cream" consistency would be the same if you started with pureed fresh bananas.