What went wrong (OG came out low)

beerguy2009 said:

I just finished brewing a Brewer's Best Engilsh Pale Ale kit and the OG came out low.
Here is what I did.
The recipe has you boil 2.5 gallons of water to make the wort. I used 3 gallons instead. I steeped the grains and added the DME, hops, and LME per the schedule. I added Irish Moss the last 15 minutes of the boil.
I then cooled the wort and added enough clean water to raise the total volume to 4 gallons. The recipe said the OG should be 1.042 to 1.046 and the total volume should be 5 gallons. The OG of my batch came out at 1.042 with 4 gallons total volume. I did add more water to bring the total volume to 4.5 gallons and the OG is now 1.040 (thought I should add water to get close to the total volume).
Why is the OG coming out on the low side? Is if because I used 3 gallons instead to 2.5 for the boil? What else may cause that?

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manticle said:

First you changed the recipe so it's not surprising you would get a different gravity reading to that suggested. Presuming the grains are specialty grains and you're not doing a minimash, water tempterature should make little difference here.

You may have read wrong or your hydrometer might be out. It's also highly possible that it was just a temperature issue: what was the temperature of the wort when you measured it? Hot wort gives lower gravity readings so you may have been spot on but read it too hot. You can use hydrometer correction calculators - here's one: http://hbd.org/cgi-bin/recipator/recipator/hydrometer.html. Usually correct for 20 degrees celsius or whatever the faranheit equivalent is. Your hydrometer should read 1000 in 20 oC distilled water so calibrate it.

Being an extract brew, correcting low gravities is as easy as adding in a touch more dry or liquid malt or dex if you want to balance out the maltiness.

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beerguy2009 said:

So does having 3 gallons for the boil instead of 2.5 change the SG? I had the same problem with lower than expect SG with the last batch that I also did a 3 gal boil instead of 2.5. Also since I add dex to carb the beer I am assuming I can add dex to up the OG if nessessary without changing the beer too much? Does using Irish moss have anything to do with it?
Just trying to get a better understanding since I am still rather new to brewing.
BTW the grains were specialty grains.

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