Film on the top of coffee

[chartist10]

When we make an instant coffee and it cools, you can see a visible film forming on the top. Is this something to do with the hard water area we are in or something else.. Oh and a solution would help. Many thanks

[bookermel]

If you use hot milk it could be the skin forming on the milk (proteins I think). If not it could be from the hard water, if so then use filtered water this should help. It does with tea!!

[heathfield]

It's the whey proteins in milk, as Bookermel says. They coagulate on top of the coffee, and evaporation dries the top surface, forming the skin.
Note that It doesn't happen with coffee creamer powders, - it's the milk that's to blame.
But if you stir for long enough, you'll dissolve the skin back into the coffee.

[BBWCHATT]

Chart - are you talking about that oily sheen that is on top of the cup of black instant coffee? I have wondered about that myself - but just assumed it was the oil from the coffee bean.

[chartist10]

Hi all yup should have made it clear I was refering to black coffee and it is a slick like film that appears

[cornsilk]

We have the same problem. I think it is due to the hard water because when we lived in South Yorkshire where the water is very soft we didn't have the problem. We live in a hard water area now. It is most unappetising and I try to skim it off the top. It is just the same with cups of tea. I think the answer is to use filtered water.

[cyclone]

I get the same with tea, it sticks to the mug when you tilt it.
Wish I knew how to get rid of it, looks horrible.