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I am an extract brewer and every brew I have done the OG was lower than the intended OG, (my OG is always lower than the recipe's OG). For example I brewed the stout recipe below from beertools.com and my OG was only 1.070 not 1.078. Assuming my hydrometer is accurate and my readings are correct. Could this be caused by not boiling malt extract long enough or steeping the grains for too long/too high temp? What causes OG to be lower than it should be?

Category Stout Subcategory Foreign Extra Stout Recipe Type Extract Batch Size 5 gal. Volume Boiled 3 gal. Mash Efficiency 72 % Total Grain/Extract 11.65 lbs. Total Hops 2.0 oz. 1.00 lbs. Maris Otter Pale info .90 lbs. Roasted Barley info .85 lbs. Belgian Aromatic info 0.60 lbs. Belgian Special B info 0.30 lbs. American Black Patent info 5 lbs. Liquid Amber Extract info 2 lbs. Dry Light Extract info .5 lbs. Candi Sugar Amber info .5 lbs. Dark Brown Sugar info 1 oz. Magnum (Pellets, 14.50 %AA) boiled 60 min. info 0.50 oz. Styrian Goldings (Pellets, 6.00 %AA) boiled 15 min. info 0.50 oz. Styrian Goldings (Pellets, 6.00 %AA) boiled 1 min. info Yeast : White Labs WLP500 Trappist Ale info

Original Gravity Predicted 1.078 Terminal Gravity Predicted 1.016 Color Predicted 32.14 SRM Bitterness Predicted 56.4 IBU Alcohol Predicted (%volume) 8.2 % 96 % overall compliance

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  • Thanks for the suggestions! I brewed a belgian ipa three weeks ago and my OG was dead on at 1.071. I rinsed the grains with water @ 170º and for the first time I did not use any tap water only bottled spring water.
    – Trav
    Jan 28, 2010 at 17:33

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Assuming you are using the hydrometer right:

It could be your efficiency in the steep. If that is the case you are working at 64% efficiency instead of 72% like the recipe says. ( 70 GU * 0.72 efficiency / 78 GU = 64.6% ) Rinse the grain bag with hot water around 170º. That will get more sugar out of the grain.

How much wort did you get? If you ended up with 5.5 gallons instead of 5 then it would be 1.070. ( 78 GU * 5 gal / 70 GU )

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it could be inefficient mashing in your minimash. Do you sparge it at all? ie when you're removing the grain bag pour a little water through the grain to try to get the remaining sugar out.

It could also be you're measuring your gravity at the incorrect temperature that your hydrometer is calibrated to. Some hydrometers are calibrated to measure accurately at 60F some at 68F and if your wort is at a different temp you will have a slightly inaccurate reading.

KOTMF has got a gravity/temperature adjustment tool on their site that I use: http://kotmf.com/tools/hydrom.php

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