Oil before hops

Question

So I recently got a propane burner to brew outside (it's way too hot to be brewing inside), and I noticed something weird. As the wort came to a boil, it seemed like there was some oil floating on top. Before, on the stove top, I had never seen this. Note, this was before any addition of hops, this was pure grain wort. Any idea what this was?

Perhaps when boiling on the stove top, the boil took so long that these oils were emulsified before the boil (longer at high temps), as opposed to a quicker boil that didn't emulsify the oils before the rolling boil took hold?

Pic to come shortly, apparently the mobile app can't do it. And apparently the website won't let me add a pic, see meta question. Not sure if this link to the pic will work, but I'll try

Answer 1

Hulled barley is about 2% fat by weight. That's almost certainly why we see a slight oil-slick on the wort before it boils.

I'm not sure why you don't see it when you're boiling inside. It could be like you say,that the rapid speed of the outdoor boil has something to do with it. Or it could be that the light is brighter outside, showing the oil more clearly.