Original Gravity question

So i just did a IIPA had about 17 lbs of grain mashed at 150. According to promash with my system i needed to collect 9.5 gallons after the runnoff and have an OG of 1.046 to hit 7.5 gallons after a 90 min boil and have a OG of 1.093. Anyways, After runoff i had a little over 9.5 gallons and an OG of 1.055. 85% mash eficiency. So figure this out for me. After the boil i had exactly 7.5 gallons but the og was 1.075. Thats a difference of .018. I even took a small sample for a refract from the fermenter before i capped it and it confirmed 1.075. I cant figure this out. I mean after the runoff if you have the correct preboil gravity and the gallon amount and then loose the correct amount of volume after the boil why would i be off? Anyone?

the only thing i can come up with is that your preboil gravity reading wasnt correct.

skiingthedeep said:

According to promash with my system i needed to collect 9.5 gallons after the runnoff and have an OG of 1.046 to hit 7.5 gallons after a 90 min boil and have a OG of 1.093.

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I don't have any kind of software in front of me, but this seems like a big gravity jump for a relatively small amount of boil off. I can't see you doubling your gravity by boiling off 20% of your water. Am I just way off here?

Was there supposed to be a sugar addition to your IIPA recipe? Late boil addition or something?

+1, promash def lied to you. 9.5gal of 1.046 is only 7.5gal of 1.058. based on your pre-boil #s, you hit what you were supposed to