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Old 07-09-2012, 08:28 PM   #1
TinHat
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Default Odd OG readings

I have just bottled 3 batches of a pale ale recipe that I have brewed several times with excellent results.

All 3 batches were made of a 13 lb grain bill, and each wash mashed for 75 minutes @ +/- 156 degrees with an initial temperature of 160 degrees. By design, the initial mash temperature was hotter than I had previously used, though the number fell to the target temp within 10 minutes of mashing in on each occasion.

All 3 were 6 gallon batches that were topped up to the lip of my 30l kettle with sparge water prior to boiling. Each was boiled for 90 minutes and cooled rapidly with a wort chiller.

Up until this point on all 3 batches, everything was exactly as expected, however, the original specific gravity reading for all three batches were odd; I received readings of 1.036, 1.038 & 1.036 where I was expecting a reading between 1.050 & 1.055.

In all three cases, the target final gravity was right on.

Are there any reasonable explanations for this anomaly? Could it have been an inaccurate OG reading?

Thank your for your thoughts.

a


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Old 07-09-2012, 08:47 PM   #2
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I'm assuming that the OG readings were after cooling and in the fermenter? How were your volumes, did you come out to 6 gal like you planned? Since you're not topping up, and assuming that this was after cooling and everything should be mixed up, unless your hydrometer/refractometer is broken I'm not sure how the OGs could be off. Now if these were taken with hot samples, or before boiling, etc. I could see it, but it sounds like you're doing everything correctly.

So if its not the gravity reading that's wrong, it sounds like your efficiency is quite a bit lower than expected. Have you calibrated your thermometer? If its reading either higher than actual (too cold to mash) or lower than actual (inactivating enzymes), I could see both really affecting efficiency. How was your crush? Everything broken up well? Is it just this recipe that is off, or have you had other batches lately come out real low?


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Old 07-09-2012, 08:48 PM   #3
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What was your temp when you took the OG readings? Also, could have had a bad crush on your grain... You said you've brewed this before reaching gravity 20 points higher, right? Any other switchup in equipment?
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Old 07-09-2012, 08:58 PM   #4
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In each case, the batch yield was pretty much bang-on at 6 gallons.

For each, OG readings were taken at approximately 90 degrees f, once the wort had been cooled, aerated, & transferred to primary.

The equipment used was identical to all previous brewings.

I assume the grain crush was executed properly, as it was done by the same machine in the same shop for all of my previous brewings.

The same thermometers have given quality readings in the past.
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Old 07-09-2012, 09:02 PM   #5
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90 is pretty high...are you pitching your yeast at that temp?
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Old 07-09-2012, 09:12 PM   #6
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I will chill to 90 degrees & then aerate the wort and transfer it to primary and then pitch yeast.

Fermentation for all 3 batches was extremely viable.
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Old 07-09-2012, 09:19 PM   #7
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Okay, so a bit off your initial topic, but might want to chill that wort quite a bit more...like to 68-70.
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Old 07-09-2012, 09:24 PM   #8
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Thank you. I will try cooling to a lower temp for future brewings.

Any thoughts on how my final product may be effected... outside of the lower ABV, that is?

a
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Old 07-09-2012, 09:31 PM   #9
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A couple of thoughts on why the low OG- the first is topping up with water. Water has an OG of 1.000, so adding it to your wort would definitely decrease the OG. The second is that if you sparge more (or start sparging now if you're not sparging) you'll increase your efficiency and then no longer need to top up with water.
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Old 07-09-2012, 09:35 PM   #10
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Thanks Yooper.

All of the water that ended up in all 3 batches was run through a grain bed during sparge.

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