Author Topic: OG Question  (Read 1364 times)

Offline flbrewer

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OG Question
« on: March 08, 2015, 12:45:53 AM »
Mark down my 4th all grain batch in the record books! I can't believe how smoothly everything went today. Of course I undershot my mash temp but a kind soul was available via text for a quick response! Oh yeah, mental note for next time...when boiling 4 gallons of wort in a 10 gallon BK, remember that your immersion chiller is somewhat pointless in chilling 3 or so gallons.

So my pre-boil OG was 1.041 (1.043 estimated in BeerSmith) and the post-boil OG was 1.056. BeerSmith called for an estimated post-boil OG of 1.051 and I'm curious why the big difference? I did have a pretty low mash temp, and mashed for 75 minutes...not sure if that matters in this case.

Offline riceral

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Re: OG Question
« Reply #1 on: March 08, 2015, 01:44:57 AM »

So my pre-boil OG was 1.041 (1.043 estimated in BeerSmith) and the post-boil OG was 1.056. BeerSmith called for an estimated post-boil OG of 1.051 and I'm curious why the big difference? I did have a pretty low mash temp, and mashed for 75 minutes...not sure if that matters in this case.

Did you correct for temperature if you used a hydrometer?

Maybe boiled off more water than expected.



« Last Edit: March 08, 2015, 01:52:36 AM by riceral »
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Offline Stevie

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Re: OG Question
« Reply #2 on: March 08, 2015, 01:52:59 AM »
Could also be caused by the wort at pre-boil not being throughly mixed.

Offline Black Sands Brewery & Supply

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Re: OG Question
« Reply #3 on: March 08, 2015, 02:09:56 AM »
was it a 60 min boil? maybe turn the heat down to not boil off so hard. 75 min shouldn't matter b/c you were converted in the first 20-30 min anyway.
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Offline flbrewer

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Re: OG Question
« Reply #4 on: March 08, 2015, 02:28:41 AM »
Yes I corrected for temps, 60 min boil, and it certainly wasn't w hard boil.

Steve, can you elaborate on mixing the wort pre boil?

Offline Stevie

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Re: OG Question
« Reply #5 on: March 08, 2015, 03:09:42 AM »
The common belief is that a pre-boil gravity isn't all that reliable until the boil starts.

Offline HoosierBrew

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Re: OG Question
« Reply #6 on: March 08, 2015, 03:37:55 AM »
+1.  My preboil readings used to be all over the place - now I take a reading a couple minutes after reaching boil. Much more consistent now.
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Offline flbrewer

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Re: OG Question
« Reply #7 on: March 08, 2015, 11:46:41 AM »
I'm more concerned w the post boil figure. First because it was quite different than planned and secondly because I'd like to know the ABV. Like someone said before perhaps it doesn't really matter.

Offline pete b

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Re: OG Question
« Reply #8 on: March 08, 2015, 12:45:01 PM »
Do you know your pre boil and post boil volumes? If so you can compare that to your estimated boil off rate so you can easily tell if gravity is higher because you boiled off more than you thought you would. If you rule that out then its probably an inaccurate hydrometer reading pre boil. The good news is it may be your efficiency that's higher than you thought.
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Offline Black Sands Brewery & Supply

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Re: OG Question
« Reply #9 on: March 08, 2015, 06:56:58 PM »
we use a refractometer and monitor our run off into the kettle and also take kettle measurements up til we hit our pre-boil vol and pre-boil OG. If we have a high efficient mash and we have a ton of sugar we just top up w/ water to hit our desired pre-boil OG. on our system we usually shoot for 1 to 1.5 points below our post-boil OG.

So maybe you had a very efficient mash and you ran off too much into the kettle? since your boil wasn't all that vigorous it seems like you had too much sugar to begin w/. You might be able to reduce the base malt by 1 lb or 2...
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Offline Frankenbrew

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Re: OG Question
« Reply #10 on: March 08, 2015, 07:57:28 PM »
You can also dilute with water (some brewers use distilled for this) if your OG is slightly higher than expected. There is a dilution tool on BrewSmith as there are on the internet. I do this all the time if I'm off more than a few points.  It's the same thing as adding sugar or malt extract if you're below your target.
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Re: OG Question
« Reply #11 on: March 09, 2015, 02:38:27 AM »
when boiling 4 gallons of wort in a 10 gallon BK, remember that your immersion chiller is somewhat pointless in chilling 3 or so gallons.

That's why I use 6 and 6.75-gallon kettles for 3.5-gallon primary volume batches.  The geometry of a smaller volume kettle is just all-around better for brewing smaller batches.  The fluid column height for three gallons in a 12" diameter kettle is approximately 3 * 231 / 36 / 3.14 = 6.13" tall.  The fluid column height for three gallons in a 14" diameter kettle is approximately 3 * 231 / 49 / 3.14 = 4.5" tall.   A difference of 1.63" may not sound like much, but it translates to 1.63 / 0.375 = 4.35 additional coils being submerged in the wort when using a immersion chiller made with 3/8" diameter tubing.  With 8" diameter coils, that difference results in over 8 additional feet of working copper or stainless steel.

Offline flbrewer

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Re: OG Question
« Reply #12 on: March 17, 2015, 12:47:15 AM »
So a quick update, I believe fermentation is pretty much done (confirming in a couple of days) and I'm at 1.004! What a low FG considering I started with 1.056, which Beersmith tells me is about 76% efficiency.

It sure doesn't taste like 6.83%, so I'm thinking my FG reading was off somehow. Any thoughts?

Offline ynotbrusum

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Re: OG Question
« Reply #13 on: March 17, 2015, 11:51:59 AM »
Of course calibration is important - I have one hydrometer that reads 2 to 3 points low (the actual Gravity is 2-3 points higher than the reading).  I marked it with red marker so I know it's the "bad one".
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Offline Wort-H.O.G.

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Re: OG Question
« Reply #14 on: March 17, 2015, 03:04:26 PM »
So a quick update, I believe fermentation is pretty much done (confirming in a couple of days) and I'm at 1.004! What a low FG considering I started with 1.056, which Beersmith tells me is about 76% efficiency.

It sure doesn't taste like 6.83%, so I'm thinking my FG reading was off somehow. Any thoughts?

Justin- this was the 3 gal batch of beer you ended up mashing in around 148F?  that ADT or apparent attenuation looks to be 92%....hmmm. I would focus on getting that hydrometer dialed in so you are confidant in all your readings. might even consider picking up a refractometer.
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