So i have been brewing extracts for awhile now and i always have a problem of my brew original gravity being lower then what the recipe is listed as. I am topping off with water, but i am mixing with a drill to aerate before i take a sample. I also am making sure i am not filling up past 5 gallons. I am also taking temperature in consideration. I have read a lot of different articles and make sure i have been doing the right things. No matter what it always seems too be really low compared to what northern brewer has the OG listed as. What am i missing here?
Is your fermentor a bucket or carboy? Some buckets have gallon markers, but they are often incorrect. Have you filled your fermentor, whether a bucket or carboy, with a measured five gallons?
Is your hydrometer calibrated? In distilled water a hydrometer should read 1.000, at the calibration temperature, of either 60°F or 68°F. The calibration temperature is printed on the card inside the hydrometer. The SG sample needs to be at the calibration temperature for accuracy. There are correction tables for when the SG sample is either cooler or warmer than the hydrometers calibration temperature. A refractometer also needs to be calibrated.
Flars is right, if you are measuring either your volume or gravity wrong because the instrument isn’t calibrated, that is going to throw off your results. And it will do so consistently as you are experiencing.
The other possible cause could be that you are not putting all the sugar into your fermentor. How much trub are you throwing away from the kettle? I’m not sure how NB did it, but many extract recipes were designed with the assumption that everything would be dumped from the kettle to the fermentor. When you leave the trub behind, you also leave some of the sugar behind with it. That could make a small difference.
In addition to flars and rebuilt’s ideas; are you getting ALL the extract out of the bottles? After dumping I would put an inch or two of hot tap water in the bottle and shake it up, then dump it in the pot. Repeat 2-3x until the bottle is squeaky clean.