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Old 08-21-2012, 07:56 PM   #1
Oct 2011
Posts: 15

So, I once again submit myself to the collective wisdom of the Beer Forum! You (the group) have been invaluable in troubleshooting a number of issues I have had around fermentation and carbonation, now I return to request your assistance in understanding why the OG on my final product differs from the OG forecasted in my recipe generator. I had one recent brew that we used a sparge calculator on, built in the grain time and strike temperatures, boiled for the prescribed time and ended up with exactly the desired 5 gal however my forecasted OG was 1.068 and it infact was 1.062!
Any ideas why this occurs? Am I burning off to many sugars in the boil? Do I need a richer grain bill? Am I completely off the mark?

Any advice is, as always, greatly appreciated!

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Old 08-21-2012, 08:24 PM   #2
Jul 2011
Glenview, IL
Posts: 6,368
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1.068 estimate OG is higher than 1.062 actual so your efficiency of mash was off a bit. Did you do a pre-boil gravity reading? Very useful tool when doing all grain so you can then see your actual mash efficiency and make adjustments in the boil time and vigor if necessary. I would also suggest you better evaluate your crush and mash method to ensure you are getting the most out of the grain. IMO if you are having the LHBS crush your grains for you it is usually found to be inadequate.
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Old 08-22-2012, 06:25 PM   #3
TopherM's Avatar
Mar 2011
St. Petersburg, FL
Posts: 3,974
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You are only off by 9%. Not a biggie. 9% won't change the final beer very much at all.

You likely just didn't get the same efficiency on your system that your recipe assumed. Next time, you could correct this by adding a bit more grain across the board, slightly finer crush, like the last poster said, or even just boil for 15-20 more minutes.

9% isn't a biggie, but you really should be shooting for the OG, NOT for the certain volume. You would have been right on your target OG for this batch if you had about 4.7-4.8 gallons as your final volume.

Oh, and sugars don't "burn off" during the boil. Only water, in the form of steam. Gravity (OG) is a measurement of liquid density, and OG goes UP the more sugars are dissolved in your water, so boiling longer reduces water volume without reducing sugar content, hence more density, hence higher gravity.
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