Pre boil vs post boil

[CemeteryCellarsBC]

Second AG and my pre boil gravity was spot on (1.041). My post boil was 1.075. Does that make sense? If so, what is my OG when calculating ABV and how does it affect my FG which is supposed to hit 1.013.

 

[d2xx]

your post boil # is your O.G. and is going to be higher than your pre boil because your boiling off water which is going to raise the gravity your basically condensing your wort. Your F.G will depend on a lot of things, type of yeast and type of beer being made. i.e. fermentable sugars.

 

[curtw]

Wow. With a pre-boil gravity of 1.041 and a post-boil gravity of 1.075, you boiled off a lot of water! brewersfriend gives these gravities for pre- and post-boil volumes of 10.0 and 5.5 gallons! (Or 6.4 and 3.5 gallons, for example.)

What was your volume into the fermentor?

 

[aeviaanah]

Second AG and my pre boil gravity was spot on (1.041). My post boil was 1.075. Does that make sense? If so, what is my OG when calculating ABV and how does it affect my FG which is supposed to hit 1.013.

did you convert gravity for temperature of wort?

 

[IL1kebeer]

Are your measuring instruments calibrated? Refractometer or hydrometer? Did you correct your gravity measurements for temperature. There was user error somewhere along the line unless you boiled for like 3 hours.

 

[Cyclman]

Sugars in wort don't change in boiloff. So to go from 1041 to 1075 would mean boiling off almost half your water. My guess is that the wort wasn't thoroughly mixed when you measured, liquids stratify quickly and if you're taking a measurement off one layer, it doesn't represent the overall composition of the liquid.

Stir gently but thoroughly when you're going to take a measurement, you'll get more accurate numbers.

I also recommend a refractometer if you don't have one, so all your measurements waste very little beer!

 

[CemeteryCellarsBC]

I should've noted that I brew small batches. This was a volume of 2.75 gallons pre boil and about 1.8 gallons post boil. My readings are all done with a refractometer and it was calibrated before brewing. The temp with the post boil reading was about 78 degrees. It's been in the fermenter for about 19 hours and is vigorous. Should I take another reading now?

 

[CemeteryCellarsBC]

Are your measuring instruments calibrated? Refractometer or hydrometer? Did you correct your gravity measurements for temperature. There was user error somewhere along the line unless you boiled for like 3 hours.

60 min boil

 

[IL1kebeer]

My guess is that the wort wasn't thoroughly mixed when you measured, liquids stratify quickly and if you're taking a measurement off one layer, it doesn't represent the overall composition of the liquid. Stir gently but thoroughly when you're going to take a measurement, you'll get more accurate numbers.

+1

OP: This is probably your problem then. If I get an off reading it's usually because the wort settled while it was chilling. I'll stir it up with the immersion chiller and the reading will be spot on.

 

[CemeteryCellarsBC]

UPDATE

24 hours in and I took a new reading: 1.051 with Hydrometer and 1.060 with refractometer. Which do I read? Is this my OG or just coming down to my FG?

 

[IL1kebeer]

UPDATE 24 hours in and I took a new reading: 1.051 with Hydrometer and 1.060 with refractometer. Which do I read? Is this my OG or just coming down to my FG?

Use the hydrometer reading. Refractometers get thrown off when there's alcohol in solution. There are charts for conversion online though.

I'd imagine your OG was a bit higher if fermentation was 24 hours in. There's no way to really tell by how much though.

 

[CemeteryCellarsBC]

So do you think the 1.072 reading post boil was a fluke?

 

[IL1kebeer]

So do you think the 1.072 reading post boil was a fluke?

Can't say for sure but I wouldn't be surprised.

 

[emprbasist]

I'm guessing your pre boil reading was off. If you started at 1.041 at 2.75 gallons and boiled off to 1.8, you should be at 1.063 post boil. I'm guessing like someone else mentioned, your wort wasn't well mixed for your pre boil sample.

 

[CemeteryCellarsBC]

Good stuff. Thanks guys. I'll go with the 1.063 and make sure to mix a bit before reading after cooling.