Gravity Reading

[SouthRidgeBC]

I was in the zone with my last brew day and took a pre boil gravity but forgot to take a post boil reading. I pitched the yeast and it's been fermenting for 2 days. Can I take a reading now and will it be relatively close to what it was before I pitched the yeast?

 

[MrHadack]

Sorry, I think you're just out of luck! Although it might be possible to get a decent estimate based on pre-boil readings if you also know the pre and post boil volumes. Do you have those?

 

[SouthRidgeBC]

Yeah I was pretty accurate. My pre boil was 1.062 with a volume of 6.75 gallons and a post boil volume of 5.25 gallons. My recipe had said that my OG should be 1.062 but that was my pre boil OG. Now I'm a little worried.

 

[billym99]

If you were 1.062 @ 6.75 gallons, after a 1.5 gallon boil off you would be around 1.079/1.080

 

[MrHadack]

I estimate your OG before fermentation to be around 1.078. It's a guess, but it is probably in the right ballpark. There is a calculator you can use HERE. In the second section of that page, you can see where it says "The target volume is known, the new gravity unknown." I just entered in the info you gave me, and got the expected new gravity (1.080).

During the boil you are concentrating the wort by removing water through evaporation, so all things being equal, that calculation of 1.080 should be in the right ballpark for the post boil volume you report. However, the reason why I hedged a bit lower with 1.078 is that I have read information that says the proteins that precipitate out during the hot break will cause a discrepancy in a direct prediction like this: in other words, material falls out of solution during the boil process, and it isn't just simple evaporation going on. I'm guessing this doesn't account for much, but it might account for a couple points.

 

[SouthRidgeBC]

This is great info thanks guys. Considering my readings and that the recipe said I should be at 1.062, should I be worried?


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[SouthRidgeBC]

It also gets me around 90% efficiency, seems high.


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[MrHadack]

Worried? Of course not! RDWHAHB. The beer will be stronger than you planned, though.

I hit 88% efficiency one time, so maybe you got lucky.

Did you temperature-correct the gravity readings?

 

[SouthRidgeBC]

The one reading I took preboil was at 70 degrees so it should be accurate.


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[MrHadack]

Well, let's say you got 90% efficiency. What efficiency were you expecting to have in order to get 1.062 as an OG? Do you use Beersmith or similar software?

 

[SouthRidgeBC]

What if I took a reading now, could I assumed the OG was a few points higher? Would it be close to the OG?


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[SouthRidgeBC]

I use ibrewmaster and it was saying 73%


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[MrHadack]

Well, I guess you just had a great mash and sparge resulting in abnormally high efficiency.

Regardless, I think you could feel confident saying the OG was around 1.078

 

[SouthRidgeBC]

Okay deal....I may take a reading tonight anyway just to see. I'm thinking it should be fairly close anyway since I am only 2 days removed from pitching. Thanks for all of your help, makes me feel much better about missing my OG reading.