Help with off flavors in my stout

So I brewed O Flannagain Standard and am finally able to draw my first pints of the keg. The beer is nice and rich, lots of roasty flavor, the bitterness is just right, maybe not quite as creamy as I would like. The one thing that tastes off is the presence of an almost metallic acidity. You get hit with the roasty flavor up front, but then it hits with that acidic flavor. Its not terrible, just not what I would prefer.

Heres the recipe I used.

6.00 lb Pale Malt (2 Row) US (2.0 SRM) Grain 64.86 %
1.00 lb Barley, Flaked (1.7 SRM) Grain 10.81 %
1.00 lb Cara-Pils/Dextrine (2.0 SRM) Grain 10.81 %
0.75 lb Roasted Barley (300.0 SRM) Grain 8.11 %
0.50 lb Chocolate Malt (350.0 SRM) Grain 5.41 %
1.00 oz Goldings, East Kent [5.00 %] (60 min) Hops 17.2 IBU

Mashed for 60 minutes at 160, then left in primary for 2 1/2 weeks at 66 degrees.

I would really appreciate any ideas on brewing practices or brew science that could explain this off flavor. Thanks

What's your water profile like? I notice that with my hard water, I get a slight metallic taste with roasted malts and certain dark beers. I don't know the science behind it, but someone else explained it to me in the past and it made sense. Hopefully, they'll be along to give the actual brew science as to why that happened to me.

How long have you conditioned it for before tapping the keg? It could just be really green.....

Fermented for 2 1/2 weeks, purged with co2 and conditioned in the keg at room temperature for 2 weeks, left it on co2 for 2 weeks at 9 psi to carb.

I really have no idea on my water profile, I use well water which taste really good as far as flavor goes, but I have no clue on the actual profile.

jmp138 said:

Fermented for 2 1/2 weeks, purged with co2 and conditioned in the keg at room temperature for 2 weeks, left it on co2 for 2 weeks at 9 psi to carb.

I really have no idea on my water profile, I use well water which taste really good as far as flavor goes, but I have no clue on the actual profile.

Click to expand...

My city water is very good, but very hard. My cottage has a well, and it has very high iron content. If you have dissolved minerals in your water, you may pick that up in the beer, particularly ones made with darker malt.