Sweet potato turned black

[Minions]

Hi,

I've just started weaning and steamed some sweet potato to mash. Some of it turned grey/black when cooking. I'm going to try again (I'll eat the grey batch myself) but does anyone know how to avoid it or if it is actually ok for baby? I'm guessing microwaving it like I would normally do for myself is the answer...

Thanks!

possibly as it wasn't fully immersed in water so they were exposed to the air and turned black .

its fine.

Thanks both. Feel like bit if a numpty...didn't think about it being exposed to air when steaming it.