Pre Boil Gravity was okay, Post boil way off

So just finished an Old Ale and something strange happened. My post boil gravity was extremely off.

Asied from a sparge malfunction (aka el stucko spargo). I collected too much wort, about a 3/4 to a gallon extra, so I decided on a 90 minute boil to bring the OG back withing my planned range. The pre-boil gravity was about 1.060. I added the extra from the second sparge after the boil had been going for about 15 minutes. Now I figured that would of knocked me down some points. The strange thing was that my post boil was only 1.073 when it should have been closer to 1.090. I did have a very rigorous boil going for the 90 minutes, more so than i usually do.

So what gives?

I'm going to double check my hydrometer. but otherwise I'm stumped.

Was the temperature different?

I factored in the temp with the hydrometer
readings. The only thing I can think of would be when I added the extra wort to the boil it was the last bit of the second sparge and that diluted the wort more than I thought it would. Still boiled everything for over an hour though.

WCrane said:

I factored in the temp with the hydrometer
readings. The only thing I can think of would be when I added the extra wort to the boil it was the last bit of the second sparge and that diluted the wort more than I thought it would. Still boiled everything for over an hour though.

Click to expand...

but even with temperature correction, a hydrometer reading with wort over 100 degrees is notoriously inaccurate. The sample must be cooled to under about 90 degrees, and then the reading can be taken and adjusted for temperature.

Obviously, one of the readings you have is wrong. Or the measurement of the amount of wort is incorrect. My experience is that the preboil reading is wrong if the wort was over 90 degrees.

I chilled all my samples (pre and post) and checked the temps, all were under 75F when I tested . I double-checked the post boil right before I pitched. It match what I took when the wort was cooling. Unless my hydrometer is broke

At least the samples tasted fine. Just a little bummed that I didn't hit my numbers...

This just means I have to brew again to redeem myself.