Grainy stale tea-like finish in brew.

[McAle]

I brewed an Espresso Stout using one can of Cooper's Original Stout, 3.0 Lb of Munton's dark DME, 1.0 lb of flaked barley (hoping to thicken the head) and 5 oz of espresso coffee. I steep the barley at 1.5 gal 155 for 30 minutes, and then rinsed with 32 oz of boiling water. Brought it to a boil and then removed from heat and added the DME. Once it was well mixed I poured to into the fermenter and added the Cooper's pre hopped extract and filled the bucket to 5.0 gal. and mixed everything together. I added the coffee to the bottling bucket with the priming sugar right before bottling on 1/23/13. This past weekend I tried a bottle. It doesn't taste bad at all but has somewhat of a stale grainy finish. I'm wondering if I used too much barley or maybe steep it too long. Any suggestions?

 

[McAle]

Oops, sorry for the double post. Didn't think the first one went through.
Once correction. I use 5 CUPS of espresso, not 5 oz.
Does anyone know what might cause the stale after-taste?

 

[unionrdr]

Not sure,but the flaked barley might need to be mashed. & 5 cups of esspreso seems like quite a bit.