60 vs 75 vs 90 min boil time?

I was wondering what the effect of the longer vs shorter boil is? I'm trying to build an IPA right now from several different recipes and they have 3 different boil times. :fro:

Two things come to mind:
1 - Boil off rate. Longer you boil, higher the SG
2 - Bitterness. Longer you boil the hops the more bitterness the beer will pick up.

It depends on the ingredients, for me. If I use pilsner malt, I do a 90 minute boil to help make sure that any precursers for DMS are boiled off.

I almost always do a 60 minute boil, though. I would guess that I've done a 90 minute boil maybe 20 times, and usually because I missed my boil volume by a lot, and needed to reduce the volume before adding my hops.

You'd have to look at the recipe to see why the recipe creator recommends a certain boil length. If there isn't any specific reason, just that they always do a 75 minute boil, I'd do a 60 minute boil.

Thanks guys, that seems to make sense, I was looking and Pliney the elder, stone IPA, Green flash, and the itmes were 90, 75, and 60 depending on how accurate the clones are.

I did a 75 for my last one and the bitterness was more than i expected to get so that was good.

My pliny clone is a 90 minute boil for big time hop bitterness extraction

Here's the recipe I'm doing with a 75 min boil:

EXTRACT
Light/Pale malt extract 6 lbs

GRAIN
American Pale 2 row 2 lbs
Crystal 10L 8 oz.’s
American Crystal 120L 4 oz.’s
Cara-pils 3oz.’s
Pale Chocolate Malt 2 oz’s

HOPS
75 min 1oz Chinook
60 min 1oz Simcoe
45 min 1oz Cascade
30 min 1oz Centennial
15 min 1oz Cascade
0 min 1oz Centennial
1oz each of Simcoe, Centennial, Cascade (2 weeks Dryhop)

Yeast
White Labs California Ale Yeast 01

Any thoughts would be welcome.

I might reduce some of the hops, I wasn't sure if a partial would give enough grain back bone to handle the hops