Original gravity way off what was stated.

[Hop fiend]

Hi there, I recently brewed a big IPA and used 4.37kg of dme and 237g of crystal malt (60), which should have given a s.g of 1.091 in 17 litres.
There was probably 19 litres in the kettle but the hops absorbed 2 litres or so. Even so it says on the recipe builder that I should have hit 1.082 if there was 19 litres. I took a gravity reading at 20 degrees C (which my hydrometer is calibrated at) and got 1.073. Did the hops absorb some of the sugar? If so why isn't this accounted for in the recipe builder? The final gravity was correct at 1.025, (which I know is too sweet for a big IPA but lesson learned, less dme, more dextrose and a more attenuative yeast.) I do a 19 litre boil with 2kg of dme then add the rest to 4 litres which get added at flame out and brings the volume back up to 19.
I brewed another IPA that day and that gave an o.g of 1.071 with only 3.5kg dme and 500g crystal malt (60) in 18.5 litres. I diluted it to 20 litres and that gave a reading of 1.055. It says it should have been 1.070. Also, it says with the yeast I used (white labs 051 with a 1 litre starter) it should have finished at 1.019 but it finished at 1.013. ???
Weird, I hope some one can help as I've read so many great things about the recipe builder but I can't rely on it at the moment. Cheers all, Ollie.

 

[Ozarks Mountain Brewery]

the later question about the final gravity is all about yeast attenuation, there is a lot that comes into play for yeast performance and there is not a set rule that we know of that tells us how well that yeast will perform, in this site the attenuation is set rather low and it effects the site gravity readings when you change it. If you have brewed a beer over and over again with a certain yeast using the same procedures then you can change the attenuation on your recipe to give the correct readings.

As far as the starting gravity again there is a lot that comes into play. and partial boils are even trickier, the amount of "water" , "boil off rate" which coincides with the diameter of your pot and how aggressive your heat source is, what elevation your at in the world, how thoroughly mixed up the dme is with the water. this makes a huge difference, the sugar can drop to the bottom while cooling and your reading can be off, Im betting thats the issue

 

[Hop fiend]

Cheers Ozarks for the response! I think you're right, I reckon the wort wasn't stirred sufficiently as the original gravities were too similar considering the difference in amounts of DME between the two brews.