Gravity question

[Abrayton]

So after brewing my first all-grain batch I do have one question. My post mash gravity was estimated at 1.045 and I only hit 1.036, however I ended up only missing my estimated OG of 1.062 by 2 points, hitting 1.060. I'm very happy about that, but confused as to how I made up the difference considering the low post mash gravity?

 

[PhillyBrewDoug]

What were your estimated and actual pre-boil volumes? You might have over-sparged and lowered your post mash gravity then your boil-off might have been enough to compensate.

Also could have been your hydrometer. Did you cool your pre-boil wort to 68* before taking the reading?

 

[Abrayton]

Pre boil volume was almost spot on. Post boil was actually a bit higher at 1.064. I boiled off about 1.5 gallons more than expected so I added 1.5 gallons back in to get to the estimated pre boil volume, took another reading after the top off and that was 1.060. I didn't cool to 68 before reading but did adjust for temperature

 

[Lefou]

So your boiled off water, ended up a bit high, diluted, and ended up very close.
As long as you adjusted for temperature on the hydrometer readings and hit your gravity range for the style, it works.

I can't boast a 100% consistency in method or being "dead on" within one gravity point.
So many variables and problems, but there are so many good creative solutions. That's why brewing is part science and part experimental art.

You know, a LOT of brewing basic science I've learned on my own puts some of the college classes I've had to utter shame.

 

[Abrayton]

Still puzzled why my post mash gravity was almost 10 points low?

 

[jbunton]

Pre boil or post mash as you call it will be low as when you boil you will be concentrating your wort by boiling it to a lesser volume making it more concentrated. My setup personally adds .08-.10 depending on how hard I boil it. My friends grainfather only concentrates by .07. Every variable will have an effect.

 

[Abrayton]

I do understand that the boil concentrates the wort but I guess I'm not clear as to why my post mash gravity was 10 points under Beersmith's estimate. In the end I hit my numbers so maybe it's not a big deal, but if it's something I need to correct I'm looking to learn how.

 

[jbunton]

Did u measure it warm and if so did you do a temp correction? I'll bet that's why. Hydrometers are calibrated to a certain temp! Mines calibrated for 68 so I have to do a temp correction when I take my preboil. Brewers friend has a handy one online

 

[chickypad]

It's difficult to say without seeing your exact volumes and numbers but I think you're saying the pre and post boil measurements don't mathematically make sense, which must point to a measurement error. Either not corrected for temp as above, or your volumes weren't what you though they were, or maybe your preboil wasn't mixed well. If you sparged you would have a mix of first and second (third) runnings with different gravities, so if it wasn't super well mixed it could lead to error. I've found that to be fairly common actually so I tend to measure first and second runnings separately and calculate from there.

 

[Abrayton]

It's difficult to say without seeing your exact volumes and numbers but I think you're saying the pre and post boil measurements don't mathematically make sense, which must point to a measurement error. Either not corrected for temp as above, or your volumes weren't what you though they were, or maybe your preboil wasn't mixed well. If you sparged you would have a mix of first and second (third) runnings with different gravities, so if it wasn't super well mixed it could lead to error. I've found that to be fairly common actually so I tend to measure first and second runnings separately and calculate from there.

That makes sense. I did not mix first and second runnings before measuring. I will make a note of that for next brew day. Thanks!