I was wondering how you'd break down Mitch Steele's hopping schedule for his recipes in his IPA book. For example, for one beer he writes "Total boil time is 90 minutes. Using only pellets, add 62.5% Columbus at the start of the boil, then add 37.5% Centennial during the whirlpool." How do you determine how much at what IBU? Thanks to anyone who can help. This is for a 105 IBU beer.
I don't have the book, but when I see recipes stated for percentages of IBUs, I use the AA% of the hops on hand to determine the IBUs at the time. 62.5% of the 105 IBUs is coming from the bittering hop addition. So in BS, put the AA% of the hops you have as a 90 minute addition and adjust the weight until you get the 62.5% of the 105 IBU that you need, which is 65.625 IBU. Use the amount of hops in your volume to get that IBU for bittering addition. You'd leave 39.375 IBU in the whirlpool to make your complete 105 IBU for the beer.
I recall in a recent (2012) show where Tasty and Doc were discussing a mini topic about extracting bitterness from the whirlpool and how to calculate it. IIRC, Tasty said to enter it as a 20 minute hop addition to factor the IBUs, but put them it at the whirlpool instead of 20 mins. You're just using the 20 min set point for IBU calculation.