Imperial Stout with cold stepping

[mambro]

I've been brewing all-grains for a while and I am about to try my first imperial stout.

This is what I am going to do:

batch size: 6.6 gallons (25L)
boil size: 7.6 gallons (29L)

9Kg (16.5 lbs) Extra Pale Maris Otter [70%]
0.75Kg (1.6 lbs) Roasted Barley [6%]
0.75Kg (1.6 lbs) Belgian Biscuit malt [6%]
0.75Kg (1.6 lbs) Caramunich I [6%]
0.75Kg (1 lbs) German Wheat [6%]
0.75Kg (1 lbs) Flaked Oats [6%]

60 mins: 55g (1.5oz) Magnum
30 mins: 20g (0.5oz) Topaz
0 mins: 15g (0.5oz) Topaz

Yeast: Safeale US-05

Expected Original Gravity: 1.094
Expected Final Gravity: 1.016
Expected ABV: 10.2%
Expected IBU: 71

I plan to cold step overnight the roasted barley.

Now I understand this is not a "classical" imperial stout. I wanted to get rid of black malt (too harsh) and chocolate malt (annoying vanilla flavour) to get to something more soft/smooth but still with roasted, tick and full flavour (and hopefully a brown head).

My questions are:
1) Is the amount of the special grains too much (particularly biscuit and caramunich)
2) Cold stepping: should that be done just for the roasted barley or also for the biscuit malt (and maybe carmunich)? Is it appropriate to do that on an Imperial Stout? I am afraid it would end up less full bodied.
3) Any other suggestion?

 

[mambro]

And what about some espresso in the second fermenter?

 

[JKaranka]

Looks like a lot of biscuit to me. Brown malt gives a dirty head but it might be too smooth for you (I'd prefer it to Biscuit). I'd use less crystal / Cara malts. Dial your efficiency lower than usual (if usually you get 70%, expect 60-65%.)

 

[JKaranka]

Btw, I wouldn't bother cold steeping. If you can't stand the roast stay away from the stout

 

[m1k3]

Have you tried adding the dark grains after the mash (before vorlauf)?
Suggested by Gordon Strong.

I've added the dark grains at the end of the mash on a Stout and a Baltic Porter.
That makes a less roasty beer.

Personally I like roasty and enjoy black coffee. I'll probably not use that method again.

Anyway, just an option before going to cold steep.

 

[mambro]

Thanks for the replies
Eventually I did as of the original post, the main screwup I see is the efficiency. I usually get 60%, this time I suspect it will be much lower.. The OG after sparging and before boiling was 1.040 :\ It will go up with boiling (boiled for 120 minutes in total) but never to the calculated target.

Mashing 11Kg of grains on a 30L buckets was not a good idea in terms of efficiency

On the other hand I tasted the cold steep roasted barely liquid before adding it at boil off and it still has a strong dark coffee flavour, so I hope for a "smooth" roasted flavour in the beer