SG not as expected

[Tricky Dicky]

At the start of a boil I took a reading after the wort had cooled to 20c in the hydrometer tube and it read 1040. I then performed the boil for 60 mins, boiled off approx 4liters then cooled the wort and at 20c took another reading it read 1038, any ideas as to why that would be?

 

[Reg Holt]

At the start of a boil I took a reading after the wort had cooled to 20c in the hydrometer tube and it read 1040. I then performed the boil for 60 mins, boiled off approx 4liters then cooled the wort and at 20c took another reading it read 1038, any ideas as to why that would be?

Could it be you took your sample at the start of boil when all the sugar was at the bottom of the kettle. Its impossible for the gravity to drop after a boil.

 

[Grmblz]

^ what he said, stratification, the heavy sweet wort is sitting on the bottom with the weak runnings from the sparge sitting on top, you take a sample from the bottom 1040, then boil which mixes that heavy with the light and results in 1030 ish which after 60 mins boiling gives you 1038 approx.
Before taking any samples give everything a bloody good stir.

 

[MaggieO]

Recipe? Be easier to see where you should have been.