High gravity beers present many unique issues, but achieving the target start gravity is a big one. Thats a really high start gravity I havent gone over 1.088 for a 10% abv belgian quad.
I try to use as little mash infusion water as possible to increase the sparge water volume. other tips:
-Add 5%to 20% more grains to compensate for loss of efficiency for high gravity mashing;
-verify complete starch conversion before sparge; sometimes takes 90 minutes sacc rest to pass iodine test
-make sure to raise the mash to 168 when done to optimise extraction,
-do at least 15 minutes of vorlauf,
-let the mash drain almost to top of grain bed while lautering then restart sparge,
- keeping sparge water at 168 might involve reheating
these are just a few things I have done to try to achieve very high start gravities. You will get much closer but rarely achieve a starting gravity that high. You may need to stop runnings at a higher gravity than 1.010, say 1.030 or higher, as this will only bring your batch gravity down.Thats what increases losses with high gravity mashing.I have heard some breweries redirect the runnings back through the mash or direct the tail runnings of one batch into the start lauter of another to capture all of the sugars. Boil longer and suffer a small volume loss to increase gravity.