From an instant coffee website:

Rocket Fuel Strong Instant Coffee with Added Guarana 100 g (Pack of 6)

1.0 out of 5 stars Filth, dirt and rankness in droves. Avoid!, 21 Sep 2012
By Mr. Tkm Cooper (REAL NAME)   
I can't even begin to describe how utterly disgusting this product is. I like my coffee, I prefer filter coffee but I like a good cup of instant now and then (I'm not a coffee snob), so when a work colleague brought this so called 'rocket-fuel' in, I thought I'd give it a go.

I made it conservatively (one teaspoon and quite a bit of milk). It looked rank. Thick and black, it looked like it was festering. Against my better judgment I took a sip. I nearly threw up. It tasted like liquid dirt and tarmac with a whole pot of marmite and bovril thrown in for good measure. I could feel my teeth dissolving and my guts churning with every gulp.

I'm sitting here with half the cup to go and I don't think I can finish it. I'm going to taste this utter sh**e for days and no amount of teeth cleaning will rid me of the taste or stench of this putrid bile.

In short. Avoid at all costs!!