Tried my hand yesterday at some old school parti-gyle brewing.
Definition here: (
http://www.homebrewtalk.com/wiki/index.php/Parti-gyle)
I started with roughly 20lbs base grain, and 10lbs of specialty. This recipe was a black IPA and would be the typical grain bill for one of my 12GAL batches of IPA.
I mashed in at a water to grain ratio of 1.6:1 and let sit for 60 mins.
I then mashed out, collecting roughly 6.5-7GAL of wort, with just enough sparge water to prevent the grain bed from going dry. I kept sparge water at 158F to bring the 148 grain temp back up to 152-154.
After mashing out, I mashed back in, trying to hit a water to grain ration of 1.4:1 and let sit.
Meanwhile, I boiled the first mash out for 60 mins, adding the approriate hops etc. Chilled and transferred 23L into a primary with an SG of 1.093
Mashed out the second mash, collecting roughly 6.5-7GAL of wort. Knowing this was a lighter version, I used half the hop bill of the previous over the 60 minute boil. Chilled and transferred 23L into another primary with an SG of 1.042.
So, the big question is....what was my grain efficiency? I know there is a calculation to estimate the SG of both runnings, just not sure about how to calculate the overall efficiency.
If my rough calculations are correct, I'm going to have 6GAL strong beer @ ~9.5% and 6GAL light beer @ ~4%.
I could have removed a couple of litres of light wort and added a couple of litres of strong wort to it to bump it up to 5%, but I didn't want to mess with anything this time around.
So, looking at what I'm left with after 2 mash-ins on the same grain bill, I now see that I've been wasting a good deal of potiential beer by throwing away grain used for stronger beers, which is typically what I brew. I think from now on, I'm going to parti-gyle when I make heavier beers...this way, I will make more efficient use of my grain, and have a weaker version of the strong style of beer that I can serve to guests or drink myself when I have things to do.