Hydrometer issues

We always seem to have strange issues with our hydrometer measurements whenever we brew. I checked it out the other day and found out that the issue comes about from making hydrometer measurements at room temperature and at mash or boil temperatures.

I know we should be making the temperature conversions from wort temperatures to room temperature and we have. But our plastic hydrometer seems to always give the similar  reading (within 0.015), no matter what the temperature the gravity is measured at. That’s really frustrating, don’t you think?


For example, we measured the gravity of the wort at the end of the boil to make sure we had boiled off enough water. Doing this at 80ºC gave us a gravity reading of 1.055 – which after converting for temperature, translates to a gravity of 1.084. After cooling the beer down to 19ºC, I measured the gravity again and found it to be at 1.061, which was much lower than our expected 1.084. I didn’t really know what was going on so I decided to further experiment with my hydrometer.


I placed some tap water into the hydrometer to ensure that the calibration was still correct. It gave me a reading of 1.000. To check the effect of temperature, I placed boiling water with the hydrometer, which gave a reading of 0.0996 – very close to 1. Therefore, I assumed that with this hydrometer, temperature calibration is pretty pointless, but still, I wanted to know why this is the case.

Leave your suggestions in the comments.

Hydrometer issues aside, this also suggests that I’m getting really sucky efficiency from my mash. I’ve never had great efficiency, but I’ve always put it down to my mash tun having 9 litres of dead space, so my mash is highly diluted. But I know lots of people that run the same system and don’t have the same issues.

Maybe my automated temperature controller has a temperature offset, but measured against a separate device, the two numbers agree to within 1ºC, so it’s not really a big difference. I would really like to solve my efficiency issues, but it just means I’ll have to buy more grains to compensate for this problem.

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  1. Not sure the reliability of the people who made the calculators. Maybe it’s only accurate within +/- 10c from the calibrated 15 or 20c. I’m sure it’s not a straight line curve over gravity and temperature.

    I’m not bothered if my beer finished at 1012 instead of 1010, but more bothered when the FG is outside the range, ie below 1020 if it is a RIS or above 1010 for a Saison.. I don’t think anyone can taste 1008 from 1012.

    Of late, I also found problems with my hydrometer (Coopers plastic ones). I had it measure 1.000 with tap water before, then another time I have it measure 3-5 points lower, then after it measured correct again. Recently, it measure 0.997 and I just threw it away. I think the glass ones are more reliable but it breaks all the time!

    I find my refractometer more reliable, and pretty close to a working hydrometer (what is 1-2 points off?) even with the influence of alcohol, and saves me alot of wort :P

    1. Its not really the FG thats the problem. That I can measure fine its the OG pre-boil and post boil that is where the issue is. I may look to see if there are other temperature calibrations that can be used to see if that helps. I find that refractometers become unreliable when reading gravities under 1.020. Therefore I prefer to stick to hydrometers.

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