Correct PB gravity but low OG

[ALExanderH]

Using Beersmith - I collected the correct pre boil volume and gravity in my two recent batches and end with the correct post boil volume into fermenter but the batch I brewed last was 7 gravity points low of the estimated 1.097 OG and the one before that estimated at 1.062 but was 5 points lower.

My measuring equipment is definitely not at fault, measure correct with water and I hit my pre boil but not original gravity. I've used both hydrometer and refractometer in both batches.

Since I hit the estimated volume into fermenter and pre boil volume my boil off can't be at fault?

 

[beskone]

Either your PBG was off, or you post boil volume was off. You can't nail PBG and expected boil off and not nail OG.

Just like you can't nail OG & Post boil volume and have your PBG or volume be off.

Perhaps your measurements are off, have you checked your hydrometer calibration, did you measure post and pre boil gravities at the same temperature?

 

[ALExanderH]

As stated in OP both hydro and refracto measure 1.000 with water and they measure the same PBG and OG and always at 20°c. Fermenter volume is obvious in plastic bucket fermenters with 1 liter increment markings. My kettle has 2 gallon increment markings and how many liters per centimeter in the kettle is and measure it with measuring tape.