Confused by screwy hydrometer readings.

Ok, I've had a situation today I can't explain, please help.

I took a preboil sample for testing measured the temp with my calibrated probe and read 1040 over three tests (once the sample had reached 20°c). This was slightly higher than expected but my efficiency estimate was based on a conservative guess when I started brewing so my recipes are always over the beer smith prediction (really must update that with current figures).

Boiled for 90 minutes with a reduction in volume of 14 litres to finish with 23 litres to fermentor.

Post boil sample monitored until 20.4°c then measured at 1040. Hydrometer checked in 20° water and confirmed reading of 1.0.

Took 5 more readings -all 1040.

How is this even possible? My head is telling me it isn't and yet I can't argue with my measurements.

I've brewed many, many times without issue, know how to take readings and am bordering on obsessive compulsive with my data acquisition and interpretation so what is going on?

Confused.

It's not possible, so you're not crazy!

First, test the hydrometer in plain water. Make sure it reads 1.000. Then see what we can do.

Any chance your hydrometer was bottoming out in the test cylinder when taking the pre-boil measurements?

Brew on

thanks for the replies- Yooper I had checked against water at 20 degrees c (just edited the post to clarify that it read 1.000 as the first edit was missing the decimal point).

Doug- everything's possible but I'd doubt this was happening as I measure by pushing down the tip of the hydrometer whilst giving a gentle spin then watching as it bobs up and down before settling out- then I read from the bottom of the meniscus in the trial jar.

Right now all I've got is my initial pre-boil reading was misread and the two subsequent checks levelled out at the same marking so confirmation bias or lack of attention caused me to believe that they're all the same in my mind if reading one was 1040 they're all 1040 rather than actually paying full attention to the numbers on the subsequent dips.

:smack::smack: