Hit OG then missed OG BIAB

[bgmac]

Weird thing happened today with my BIAB batch. I have been using the same grain bill each brew session with just minor tweaks each time (trying to perfect a juicy pale ale). I usually hit a pre-boil OG of about 1.050 and a post boil OG of about 1.060. Nailed my mash temp at 152.5 - 153 for the full 60 minute mash. Pre boil OG was 1.050 as predicted. I sparge till I get to 13 gallons in the kettle and almost always see it reduce to 11 gallons from boil off at the end of a 60 minute boil (2 gallon loss). For some reason this time I ended at 1.053 and not the standard 1.060 that I consistently get with my predicted 2 gallon loss ending at 11 gallons. I know that boiling wort only losses water through evaporation and cant figure out why the post boil OG was low, kinda like the sugar went somewhere. Using an online OG FG calculator shows that I should be at 1.060 post boil OG. I trust the markings on my Kegco 20 gallon kettle as I have tested it with gallon jugs when I first got it. I use the standard glass floating hydrometer at 70F wort temp to test every time so don't think that's the issue. This is probably not a BIAB issue and maybe something else? Has anyone ever run into this and figured out the cause of this weird symptom?

 

[wilserbrewer]

Bogus volume and / or gravity readings somewhere in the process.

Numbers don’t lie...people do lol just kidding...

Sorry I’m no help...

 

[bgmac]

No worries, I'm not really an ABV snob. Just thought it was weird. Maybe my temp was off a few degrees when I checked the gravity hopefully. Thanks for reminding my about the human factor that can throw things off from time to time.

 

[NobleNewt]

I had a similar experience outlined in this thread: https://www.homebrewtalk.com/forum/threads/random-bizzare-efficiency-question.664404/

Turns out, I think I misread my refract and didn’t take any hydro readings. Just bottled it today, and it tastes delicious! I’m sure yours will too.

 

[bgmac]

You are right. Probably a minor mistake on my part. I thought I had my brewing process down to a science at this point but think my temps where slightly off when I took my OG readings.

 

[doug293cz]

When sparging you need to make sure your wort is completely mixed prior to taking a pre-boil SG. Otherwise you could pull a sample from a region of higher or lower SG than the average. This is probably the most common form of measurement error when you have the situation of:

Pre-Boil Vol * (Pre-Boil SG - 1) ≠ Post-Boil Vol * (Post-Boil SG - 1) [The odd character in the middle is a "Not Equal" sign] ​

A note on your terminology. OG (original gravity) is only used for the SG (specific gravity) going into the fermenter. In almost all cases post-boil SG is equal to the OG (you'd have to add something post-boil for this not to be the case.) There is no special term for pre-boil SG, so you just have to write it all out.

Brew on

 

[NobleNewt]

You are right. Probably a minor mistake on my part. I thought I had my brewing process down to a science at this point but think my temps where slightly off when I took my OG readings.

Yeah, if you've got everything dialed in then it was probably a measurement error. That's what happened in my case. I had everything dialed in: efficiency, volumes, boil off, etc. I just trusted my refract too much!

 

[Dory Rules]

Different lot of malt? Maybe a difference in the grains.