Pre-boil Gravity OK but Low OG

[TheWoods]

Hi,

This is my first post but been reading this forum a lot. I want to thank everybody for helping me during my first 5 AG Batch. 3 out of 5 batch went well in gravity and volume measurement and was pretty much in the target Beersmith gave me. My last batch I made was a DIPA of 35Lfinal volume and 527g of hop. When I took my pre-boil gravity I was 2 point under the Beersmith estimate. My OG was 9 point under. The volume of wort was pretty much at the 35L mark.

I remember my first IPA batch I had an higher pre-boil than OG and I found in this forum that we should take the measurement when the boil begin to make sure it have time to stir a little.

But now I think that I didn't take my OG reading are the right time. What I do is I cool the wort with an immersion chiller, once I have the right temperature I remove the chiller and make a whirpool for 2 minutes and let it sit 10 minute. My kettle have a valve at the bottom and I put my fermentation bucket under the valve so the wort is splashing in the fermenter. this is when I take my sample for OG. Is there another way I should do?

On a second note I did my first starter for this batch and I forgot about the stir bar in my flask so I throw it in my fermenter. Should I try to remove it or let it there for the week.

Thanks in advance for your answer and if I'm not clear let my know since my first language is French I probably make some errors.

 

[Conan]

What temperature was your OG at? Most micrometers in the U.S. are calibrated for 60F (15.5C) and need a correction factor applied if the sample is warmer or cooler. I'm guessing you sampled at 80F (26.6C). Use the link here: http://hbd.org/cgi-bin/recipator/recipator/hydrometer.html to correct your OG.
The stir bar is fine to stay in the fermenter, too. Good luck! Kyle

 

[TheWoods]

I put my sample in the freezer until I get 20*C-30*C and then I use the beersmith tool for correcting the SG




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[Misplaced_Canuck]

Without knowing all the specifics, I will guess that your volumes were not calculated correctly.

e.g.:

If you have 25L at SG 1.045, the same wort, when boiled down to 20L, should have a SG of 1.056.

End of boil SG = 1 + (original volume / end volume * (1- pre-boil SG))

MC

 

[DSorenson]

it is also possible that the pre-boil sample wasn't mixed thoroughly. That's happened to me, but generally it gives me lower pre-boil numbers.

 

[TheWoods]

Beer smith calc:

Pre-boil vol. : 45L
Est. pre-Boil SG : 1.056
Est. OG : 1.073
Post-Boil Vol. : 36.4L


My Measurement:

Pre-Boil Vol. : 47.5L
Pre-Boil SG : 1.054 I did mix it well and waited 2-3 minute boil to make sure it is mixed.
My OG : 1.064
Post-Boil Vol. : 37L

2 Batch earlier I had A pre-boil SG higher than post-boil and somebody told me about the mixing thing. But now I thought I did well.

Anyway I'll try to mix it better during my sampling. Do you know the best way to take the OG? Can I take my sample during the last minute boil?

 

[Conan]

I take my OG sample from the fermenter just before pitching and closing it up. A wine thief or Turkey baster works well. Kyle

 

[jbaysurfer]

I would find your "getter magnet" and try to pull that stir bar up the fermenter wall and out of where the yeast cake will be forming. Then you can retrieve it the first time you take a fermenter sample, and avoid having to sift through a lot of yeast and trub debris later on when you're cleaning your fermenter in order to get the stir bar back. Also, it's easier to forget about your stir bar if you just leave it be until fermentation is all done.

I'll leave the other question to everyone else. My guess is that your boil off rate isn't quite dialed in..and yes I know you said the mark it right at where you were aiming, but something has to give. Sugars don't disappear while you boil.

 

[Ramarok]

Based on your posted volumes and Pre-Boil measurement, you OG should have been 1.071. My guess is that after your whirlpool and then letting it settle, some of your denser sugars sunk to the bottom of the kettle. Thereby throwing off your OG measurement.

If you are positive in the correctness of your pre-boil measurement and your volumes then that would be the only explanation.

I would take Conan's advice and take your OG measurement after transferring to the fermenter (it's mixed up again) or take a sample right at flame out of your boil before chilling/whirlpooling.

Hope this helps. Good luck and happy brewing!

 

[TheWoods]

Thank you all guys I'll try these advice

Cheers



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