Brewing an American IPA today, 17 pounds of grain 5 gallon batch. I think that this may be a good opportunity to make a second brew (parti-gyle). How would be the best way to determine the amount of hops to add for the second? This was totally unplanned, I believe I will have sufficient pre boil gravity on the second runnings as I do not require a large amount of sparge water on the first batch.
“Often the second wort was even boiled with the hops from the first batch.”
https://www.morebeer.com/brewingtechniques/library/backissues/issue2.2/mosher.html
I read through that, it does not mention how to calculate for hops. Just gravity of the different runnings
You may have to operate on the fly a bit for this to work. Once you have collected your second runnings into the kettle and got your boil going for a couple minutes to eliminate any stratification of your wort, you will have to take a gravity reading (either with a hydrometer or refractometer) to get a rough estimate as to a pre-boil gravity. Then plug that into some brewing software and add your hops alpha acids to calculate a potential bitterness value.