Pre & Post Boil Gravity

Several weeks ago I was brewing with someone and we used my refractometer to check the pre & post boil gravity. Both were 15.5.

We thought this a bit odd but chalked it up to "maybe we didn't mix the wort enough" or "maybe we just mis-read the thing."

Today, I brewed again, my pre-boil gravity (temp about 150F) was 11.4 (target was 15.3) and my post-boil was 11.4 (chilled wort) as well. I stirred the pot and checked the pot-boil several times with identical results.

The refract is an auto-temp adjust and I calibrated it today before I used it.

I never saw this kind of thing with the hydrometer. (Next time I will use the hydrometer AND the refract ... )

Does anyone have any ideas on what might be causing this?

 

You could use extract and make a sample with a known gravity, run it through the refractometer and your hydrometer. If you get the same weird result I'd say it is time for a new piece of equipment.

 

Being half drunk at the time I thought it was me reading it wrong.
What did you brew?

 

Even with an auto temp adjust feature you still need to cool the wort to get an accurate reading. A refractometer is only accurate in a specific temperature range, the ATC feature takes an initial reading and calculates an adjustment to compensate for the temp difference. It doesn't do anything to correct an inaccurate initial reading taken outside of the temp range. Try cooling the sample to ~ room temp before taking the reading next time and see what happens. The nice thing about refractometers is that the sample needed is so small that it's quick and easy to cool it.