Brewing with Grainfather system. Gravity measured post boil at 1.068. Gravity measured post cooling and transfer to fermenter @ 1.058. How/What could cause this?

  • 4
    What temperature did you measure at? Did you leave sanitiser in the fermenter? Is there any way water could have gotten in?
    – Frazbro
    Commented Jan 19, 2020 at 22:15
  • 1
    If there was no alteration to the wort then it is not possible for this to have happened. As liquid cools it becomes more dense. Gravity readings are a measure of density. Ergo, the cooler the wort the higher the density and higher the gravity reading. Did something else happen during cooling? As Frazbro suggests, could water have gotten into the wort?
    – joe92
    Commented Jan 20, 2020 at 9:54

4 Answers 4


How did you measure the gravity? Hydrometer or refractometer?

What temperature did you measure at post-boil? What temperature did you measure at post-chill?

The change in gravity is expected. Your gravity measurements need to be calibrated for temperature. You can use https://www.brewersfriend.com/hydrometer-temp/ to do this or have a paper copy of a calibration table on hand.

Also, if you are measuring gravity post-boil with a glass hydrometer, be careful! I can shatter due to high temperatures or temperature shock!


Really the only thing that would account for a .010+ variance is that the first sample was concentrated with more sugars than the second. Temperature cannot account for such + to - swing with any gravity meter. A hydrometer would read less gravity at hotter temps since the hotter water is expanded and has more volume and less density, objects floating in them have less buoyancy causing a hydrometer to read lower than actual SG when at proper temp.

In simple terms the wort was not fully mixed during the first sample and was more evenly mixed at the second sample.


Measurement at different temperature can cause this.

Use this site to adjust the measurement depending on the temperature: https://www.brewersfriend.com/hydrometer-temp/

Sedimentation can also change the value a little, but that would take some time.


One other alternative, check your cooler for leaks!

If you've accidentally diluted the wort, it'll have a lower gravity.

  • I have had such a problem before, also runs the risk of contamination as your cooling water will usually not be steralized/sanitised..
    – Mr_road
    Commented Jan 31, 2020 at 15:31
  • Absolutely, I've had the same happen, had so much extra water I had to boil for another half hour!
    – RYFN
    Commented Feb 1, 2020 at 10:48

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