90 minute IPA pre-boil volume?

Greetings, I'm brewing the Lil Sumpin IPA recipe from the October BYO issue today and it calls for a 90 minute boil and final volume of 5 gallons. I use a keggle for my boil kettle and have a banjo burner. I assume my evaporation rate is similar to others with the same system. My question is, how much should I increase my pre-boil volume for the extra half hour? Will it matter much? I was thinking about starting with 7 gallons, which usually yields 5.5 gallons. However, as I type this, I'm wondering if I should go to 6.5 gallons pre-boil and not worry about the extra half hour. I'm also adding a 2 liter starter, which will obviously add 2 more liters to my final volume. Any thoughts.

PS. It's about 40-45 degrees outside.

When doing 90 minutes boils I like to start with 8.5 gallons. I lose about 1.25 gallons an hour, so this leaves me right around 6 gallons at the end. I know thats more than you are looking for, but I typically leave half a gallon in the kettle with all the "material".

I've read that the isomerization of the hop oils for bittering takes about an hour. How much do you gain by boiling for 90 minutes or do you just get more darkening due to the Maillard reaction?

RM-MN said:

I've read that the isomerization of the hop oils for bittering takes about an hour. How much do you gain by boiling for 90 minutes or do you just get more darkening due to the Maillard reaction?

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Not real sure. The BYO Recipe just said to do so. Anyway, I decided to stick with 7 gallons to end up with 5 gallons of final product. It may have even been more than I needed, as I ended up with about 5.5 gallons. The odd thing is that I ended up about 10 points below the gravity I was shooting for. So, I improvised and added about a pound and a half of light DME toward the end of the boil. The only thing I can think of was that the recipe called for 4 lbs of Wheat Malt, I used white wheat malt, not really knowing the difference. Oh well, RDWHAHB.

I have red wheat malt. The difference it the color it lends to the beer with the red being slightly darker.