I just wanted to follow up on this thread with the results of my brew session in case anyone was curious, or if it is helpful for future brewers.
My digital thermometer has been very temperamental lately so I used a new standard thermometer that I received for xmas, although without verifying its accuracy. When measuring the strike water, they were 10-12 degrees apart and I chalked it up to my digital's continued issues. In retrospect, that may have been accurate and the new one was the one that was off - during the boil, the new thermometer was reading only 200.
For the first batch, I had 18.5 lbs grain to make a 5-gallon AG batch of
BrewPastor's Russian Unorthodox Imperial Stout.
I mashed with 5.75 gallons water at 170 degrees which resulted in a 153-degree mash. After an hour, I drained and sparged with 3 gallons of 170-degree water for 15 minutes, drained that, and sparged with 2 more gallons of 170-degree water for another 15 minutes.
I could not fit it all in my 8-gallon brew kettle so I put in as much as I could and returned the excess to the mash tun for the partigyle stout. It was within a half inch of the brim of my kettle so I decided to opt for caution and removed about 2 quarts, adding one to the mash tun and returning the other to the kettle after it boiled down a bit. This batch took 2.5 hours to boil down to 5 gallons and ended up with an OG of 1.082, far from the 1.111 of the recipe.
In talking to another brewer on here who had attempted a 5-gallon batch of the same recipe, he actually drew 14 gallons of wort and boiled it down to 5.5 over 5 hours. I didn't realize it would take anything that extreme to get the high starting gravity, but it makes sense now.
To make sure the second batch had enough color and flavor, I steeped 4.5 lbs new grains (4 lbs pale 2-row, .25 lbs chocolate malt, .25 lbs black patent) in 2 gallons of 153-degree water for an hour. I added the entire pot to the previous 18.5 lbs of grain in the mash tun, along with another gallon of water at 185 degrees to raise the temperature, which settled right around 153.
After about 20 minutes I drew off the wort (~3.25 gallons) and added another 3 gallons at 185 degrees, which resulted in a stable temperature of 163 degrees. After about 25 minutes I drained everything I could get from the mash tun and brought the wort to a boil. This batch resulted in 4.8 gallons post-boil, with a gravity of 1.046. I also added 4 oz Ghiradelli chocolate and will add some coffee/espresso when I keg it.
It was a marathon brew day but very interesting and creative. It's fun to think a little outside the box. I think both beers will turn out well, even if the first is on the lower end of the Imperial Stout spectrum. If you are feeling adventurous and have about 8 hours on your hands, or two large brewpots and 5-6 hours, I would definitely recommend it!
