OG Issue - Kinda Annoying

[sjuguy]

So I took a reading with about 5 min left in the boil with my refractometer, OG was around 1045 (which was the target). Once I transferred the wort into my carboy and aerated, my OG reading was down to 1040.

I did a full boil, started with roughly 6.5 gallons and ended up with about 5.25 gallons, so I didn't add any top up water. Temp should not have made a difference as the liquid on the refractometer should adjust to room temp almost immediately.

What's going on? Perhaps the "sludge" on the bottom of the boil kettle is the cause of the variance.

Any thoughts?

 

[RLinNH]

Bad reading from the boil kettle. The wort was to hot for an accurate reading. Persoanlly, I dunk a sanitized small glass into the kettle if I want a reading during the boil. A small amount cools to about 70 degrees in a matter of minutes.

 

[Dynachrome]

You boiled off 20 percent-ish.

How many pints of water per pound did you figure?

I'm wondering if the aeration might have changed the SG.