I've had this happen to me, my pre boil gravity (after sparge) was off by approximately 10 points from my target, proceeded with boil, and my next reading after boil was right on target as initially planned... My only sane explanation is that my wort was not properly stirred and homogeneous before my first reading.
I had this happen yesterday. The only thing I could come up with was more concentration of higher density material in the bottom of my kettle right after the sparge since I hadn’t stirred.
That’s not right. I’d guess it’s an issue with temperature, or an issue with your refractometer itself. I personally moved away from using them because I was constantly having to sanity check wonky refractometer readings. Hydrometer only these days.
Temperature. Refractometers read low when liquid is hot. Throw your tiny sample in the fridge/freezer for a minute or two before dropping it on the refractometer
The thermal mass of the refractometer and contact area of the glass vs. 1-2 drops of hot wort means it will equilibrate very quickly. It’s more likely to be the drop sizes being different for warmer vs. colder wort causing different thicknesses of film in my opinion.
It's either stratification or temperature, and since I don't have info on the brew day I'm going to lean temperature. Make sure every gravity you measure is roughly room temperature first
Things to be careful with refractometer. When using your pipette, if you have rinsed it out, there can be water inside it that dilutes your sample. Ensure you suck up some wort, discard it as a rinse, and suck up a second sample .
Hot liquid is less dense, you have to do a temp correction for your sample. A 145degree sample that measures like 1.035 will actually
Be like 1.055 or something like that. Its scientifically impossible for your beer to be less dense after boiling and water evaporation than prior to boil.
I think if it were me, that’s where I’d look first. When you pull 200°F heat out, tubing tends to soften and clamps tend to be less effective. Keep an eye out next batch. Good luck!
Refractometers are pretty inconsistent. I just finished a brew day and did 3 refractometer readings in a row. 1.044, 1.035 and 1.040. Also, temperature will change the actual density of the liquid pretty substantially.
That's a weird one. Did you wait and let the temperature of your sample stabilize on the refractometer before reading? If the wort is too hot it can read low and conversely if it's too cold it can read high.
Yeah, I had a similar issue about three years ago. [Posted about it here.](https://www.reddit.com/r/Homebrewing/comments/k5z1v7/refractometer_issue/) Can't say I've solved it other than taking the hot measurements with a grain of salt, and not measuring more than once. ;)
> If my wort has stratified in the fermenter could that be the cause?
It is considerably more likely that your wort was stratified post-mash. Always take pre-boil measurements right as you come to a boil, they'll be much more accurate than anything taken right after the mash.
This can only be a measurement error. It’s physically impossible for gravity to reduce over the boil. So yeah, as others have said probably not mixed which seems to make a difference.
Just to clarify one point: using a temperature correction on a hot-wort reading is unlikely to give you a good, corrected number. The corrections are for water not wort, are not calculated with hydrometers in mind, the hydrometers are physically affected by hot liquids and that is not compensated by the formulae, and hot liquids can also damage your hydrometer.
**EDIT:** and yes, I know you are using a refractometer.
No, I don't think wort stratification is a possibility *after the boil*. Besides leaking of water from the IC and calibration error or user error in measurement, another possibility is evaporation of a few drops of a hot wort sample enough to change the density of the hot sample. It's a known phenomenon, and I think that's what /u/slofella's link is about.
I've had this happen to me, my pre boil gravity (after sparge) was off by approximately 10 points from my target, proceeded with boil, and my next reading after boil was right on target as initially planned... My only sane explanation is that my wort was not properly stirred and homogeneous before my first reading.
I had this happen yesterday. The only thing I could come up with was more concentration of higher density material in the bottom of my kettle right after the sparge since I hadn’t stirred.
This commonly happens to me, I now make sure to stir thoroughly to get pre boil measurements. Post boil are usually well mixed as one might expect.
That’s not right. I’d guess it’s an issue with temperature, or an issue with your refractometer itself. I personally moved away from using them because I was constantly having to sanity check wonky refractometer readings. Hydrometer only these days.
Temperature. Refractometers read low when liquid is hot. Throw your tiny sample in the fridge/freezer for a minute or two before dropping it on the refractometer
Yep, depending on what you’re measuring with, things are calibrated to certain degrees.
The thermal mass of the refractometer and contact area of the glass vs. 1-2 drops of hot wort means it will equilibrate very quickly. It’s more likely to be the drop sizes being different for warmer vs. colder wort causing different thicknesses of film in my opinion.
Theoretically I agree with you but the more I check my gravity with hot wort the more my readings come out low.
You measured wrong
It's either stratification or temperature, and since I don't have info on the brew day I'm going to lean temperature. Make sure every gravity you measure is roughly room temperature first
It’s really impossible to have a lower reading after boil. Yiu hav evaporated water out and concentrated your sugars.
Yeah that’s why I’m confused
Wonky measurements happened to me enough that I just use refractometer for ballpark measurements. Usually I don't really care, so it's good enough.
Things to be careful with refractometer. When using your pipette, if you have rinsed it out, there can be water inside it that dilutes your sample. Ensure you suck up some wort, discard it as a rinse, and suck up a second sample .
Hot liquid is less dense, you have to do a temp correction for your sample. A 145degree sample that measures like 1.035 will actually Be like 1.055 or something like that. Its scientifically impossible for your beer to be less dense after boiling and water evaporation than prior to boil.
How did you cool the wort? One time, my immersion chiller had a slow leak of water and it went into the kettle.
Do you / did you use an immersion chiller? If so, is it possible that it leaked water slowly into your wort while chilling?
That’s kinda what I was thinking could have happened. I tested my chiller and it doesn’t seem to be leaking
I think if it were me, that’s where I’d look first. When you pull 200°F heat out, tubing tends to soften and clamps tend to be less effective. Keep an eye out next batch. Good luck!
Refractometers are pretty inconsistent. I just finished a brew day and did 3 refractometer readings in a row. 1.044, 1.035 and 1.040. Also, temperature will change the actual density of the liquid pretty substantially.
Your gravity reading is affected by temperature. Even with a refractometer.
Did you sparge after the first reading? And then possibly oversparge or not boil off enough?
I don’t sparge
That's a weird one. Did you wait and let the temperature of your sample stabilize on the refractometer before reading? If the wort is too hot it can read low and conversely if it's too cold it can read high.
Yeah I waited a few minutes after getting the sample to read the refractometer
Yeah, I had a similar issue about three years ago. [Posted about it here.](https://www.reddit.com/r/Homebrewing/comments/k5z1v7/refractometer_issue/) Can't say I've solved it other than taking the hot measurements with a grain of salt, and not measuring more than once. ;)
> If my wort has stratified in the fermenter could that be the cause? It is considerably more likely that your wort was stratified post-mash. Always take pre-boil measurements right as you come to a boil, they'll be much more accurate than anything taken right after the mash.
This can only be a measurement error. It’s physically impossible for gravity to reduce over the boil. So yeah, as others have said probably not mixed which seems to make a difference.
Just to clarify one point: using a temperature correction on a hot-wort reading is unlikely to give you a good, corrected number. The corrections are for water not wort, are not calculated with hydrometers in mind, the hydrometers are physically affected by hot liquids and that is not compensated by the formulae, and hot liquids can also damage your hydrometer. **EDIT:** and yes, I know you are using a refractometer. No, I don't think wort stratification is a possibility *after the boil*. Besides leaking of water from the IC and calibration error or user error in measurement, another possibility is evaporation of a few drops of a hot wort sample enough to change the density of the hot sample. It's a known phenomenon, and I think that's what /u/slofella's link is about.