Gravity readings

[gpalkar]

Correct me if I'm wrong.

After collecting wort in a vessel, I take the pre-boil gravity using a refractometer. Won't the readings be different at different levels in the vessel? At the top, the gravity will be low while at the bottom, it will be high. What's the correct way of taking the reading?

 

[doug293cz]

Correct me if I'm wrong.

After collecting wort in a vessel, I take the pre-boil gravity using a refractometer. Won't the readings be different at different levels in the vessel? At the top, the gravity will be low while at the bottom, it will be high. What's the correct way of taking the reading?

Wort stratification is definitely an issue affecting SG readings when any kind of sparge is done. If batch sparging, you can measure the first runnings and spage SG's (in MLT before run off), and then do a run off volume weighted averaging to get your pre-boil gravity.

If fly sparging, to get an accurate reading, the wort needs to be homogenized by very aggressive mixing. One strategy is to boil thru the hot break to allow mixing, and then taking the "pre"-boil SG reading. You may or may not want to apply a "fudge factor" to the reading based on the percent of total boil time before taking the reading.

Brew on

 

[CGVT]

Uh...mix it up before taking a reading?

 

[Revvy]

Uh...mix it up before taking a reading?

That's what I do if I'm taking a reading- give it a bit of a stir.

 

[hottpeper13]

At 10 min into the boil I take out ~1L and chill it for a vitality starter. I use a small amount for a hydrometer sample,and put the sample back in the boil when done.

 

[SlitheryDee]

I aerate the wort by agitating the fermenter for a few minutes, which also mixes it pretty well, so I take my gravity measurement after doing that. If you do that you have to sanitize whatever you're collecting the wort with, and you probably don't want to return the sample to the fermenter, but it has the added benefit of being close enough to your hydrometer's calibration temperature to be accurate.

 

[kh54s10]

I aerate the wort by agitating the fermenter for a few minutes, which also mixes it pretty well, so I take my gravity measurement after doing that. If you do that you have to sanitize whatever you're collecting the wort with, and you probably don't want to return the sample to the fermenter, but it has the added benefit of being close enough to your hydrometer's calibration temperature to be accurate.

But the question was about a pre-boil measurement.


Stir it well then take the measurement.

 

[SlitheryDee]

But the question was about a pre-boil measurement.


Stir it well then take the measurement.

Oops. Missed that somehow. :smack:

Yeah I don't see any reason not to just give it a good stir before taking a sample.

 

[doug293cz]

That's what I do if I'm taking a reading- give it a bit of a stir.

I have found thru experience that it takes quite a lot more than "a bit of a stir." I recommend getting the wort into a good strong whirlpool with your mash paddle, and then reversing the direction to another good strong whirlpool. Although if you're doing LoDO, then you're not going to want to stir. In the LoDO case, sample early in the boil, and correct for estimated volume loss at that point.

Brew on

 

[kh54s10]

I have found thru experience that it takes quite a lot more than "a bit of a stir." I recommend getting the wort into a good strong whirlpool with your mash paddle, and then reversing the direction to another good strong whirlpool. Although if you're doing LoDO, then you're not going to want to stir. In the LoDO case, sample early in the boil, and correct for estimated volume loss at that point.

Brew on

I think you are taking it too literally. Give it a bit of a stir. Enough to mix any stratification...... It is not difficult. Sometimes it is gentle other times it takes more. I take several readings to be sure.

 

[doug293cz]

I think you are taking it too literally. Give it a bit of a stir. Enough to mix any stratification...... It is not difficult. Sometimes it is gentle other times it takes more. I take several readings to be sure.

I'll stick with having to stir like a madman to homogenize a large volume of stratified wort. I usually do 5.5 gal BIAB (no sparge) batches in a 15 gal kettle. I did an 11 gal batch in Dec that required a sparge. I did a gentle stir, and got a pre-boil gravity of 1.0396 on 12.8 (temp adjusted) gal. I got a post-boil gravity of 1.058 on 11.1 gal (cooled.) This works back to a pre-boil SG of 1.0503. So, about 10 - 11 points low from the gentle, and inadequate, stir.

Brew on

 

[CGVT]

I have found thru experience that it takes quite a lot more than "a bit of a stir." I recommend getting the wort into a good strong whirlpool with your mash paddle, and then reversing the direction to another good strong whirlpool. Although if you're doing LoDO, then you're not going to want to stir. In the LoDO case, sample early in the boil, and correct for estimated volume loss at that point.

Brew on

Seems like overkill to me, but whatever works and a person is comfortable with is the right way to do it.

 

[kh54s10]

I'll stick with having to stir like a madman to homogenize a large volume of stratified wort. I usually do 5.5 gal BIAB (no sparge) batches in a 15 gal kettle. I did an 11 gal batch in Dec that required a sparge. I did a gentle stir, and got a pre-boil gravity of 1.0396 on 12.8 (temp adjusted) gal. I got a post-boil gravity of 1.058 on 11.1 gal (cooled.) This works back to a pre-boil SG of 1.0503. So, about 10 - 11 points low from the gentle, and inadequate, stir.

Brew on

This has not been my experience. I have rarely had to stir very hard to get an accurate reading. Sometimes more sometimes less......

 

[Special Hops]

stir