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Old 04-29-2013, 07:27 PM   #1
Micmacman
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Default Adjusting Pre-Boil Gravity Question

Hello guys, Been doing a porter yesterday and ended up with a little bit high Pre-Boil reading using an ATC refractometer.

The recipe called for a OG of 1.058 @ 5.25G @ 75% efficiency.
My Pre-Boil volume was 8Gallons. ( Yeah i'm loosing quite alot of wort while boiling.)
I then figured out my Pre-Boil gravity should be 1.038 (58 x 5.25/8)
I took a reading using the refractometer and found a PBG of 1.043.

A little bit high I decided to adjust it. 1.043 - 1.038 is a 5points difference.
(5 point/38 = 13.15% x 8Gallon) = Adding 1.05Gallon water.

I then added the desired water to my Pre-Boil wort ended up with 9Gallon and removed 1 Gallon so i then get 8Gallon again.

Took a second Pre-Boil Reading using the Refractometer. BAM 1.038 as expected i was really happy.

I then boiled my wort for 60min ended up with i little more wort then expected
(5.75G vs 5.25G). Took i final reading both using my refractometer and hydrometer once the wort was cooled. Ended up with an OG of 1.052 (Expected OG was 1.058)

I wondering what i did wrong. I mean i adjusted my Pre-Boil gravity. Got it right were it needed to be. But ended up with a lower OG than expected.

Should i just have boiled a little bit longer to get to 5.25 gallon and gain some more efficiency point ?

Thank you

David

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Old 04-29-2013, 08:31 PM   #2
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Provided that you could plan ahead for your hops additions, there's nothing wrong with boiling off some excess water to increase your OG, though I don't know if boiling off half a gallon would be enough to increase your OG by 0.006 or not as I'm just now learning the math. Either way, I don't think there's anything wrong with your OG not matching perfectly. Maybe just examine your process and find out how you can improve it next time.

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Old 04-29-2013, 08:36 PM   #3
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One question: ahow did you measured the final volume of your wort at the end of the boil? maybe it is just a combination of two factors:

- 5.75 G vs 5.25G you should loose something like 3 to 4 pts
- maybe you have measured 5.75 Gal, but in truth it was something like 5.8-5.9...

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Old 04-29-2013, 08:41 PM   #4
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Yeah , i figured out it was about 5.75 with the gauge on the fermenter but as you said maybe it was 5.8-5.9,

Would boiling of like 30more min would really play on my hop addition. Let says on that brew i had 2oz of Fuggle @ 60min. but i then boil for 90 min to get my gravity. Would it screw up my hop efficiency ?

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Old 04-29-2013, 08:42 PM   #5
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"Should i just have boiled a little bit longer to get to 5.25 gallon and gain some more efficiency point ? "

You aren't gaining efficiency. Efficiency is just the sugar you extracted divided by the possible sugar. Once the wort is in the pot, you can't increase your efficiency because you can't create any more sugar. (you could throw out some wort and decrease your efficiency)

By the numbers 8 gallons of 38 = 304. 5.75 gallons of 52 = 299. That is as the difference of 4 points is just measurement error (you can't really tell 5.75 from 5.80 in a bucket).

If you would have boiled down to 5.25 gallons as planned, then you would have 304 (or 299) / 5.25 = 58. You've got the exact right amount of sugar, you just didn't account for your boiloff rate properly.

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Old 04-30-2013, 03:26 AM   #6
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Quote:
Originally Posted by Micmacman View Post
Yeah , i figured out it was about 5.75 with the gauge on the fermenter but as you said maybe it was 5.8-5.9,

Would boiling of like 30more min would really play on my hop addition. Let says on that brew i had 2oz of Fuggle @ 60min. but i then boil for 90 min to get my gravity. Would it screw up my hop efficiency ?
Adding thirty minutes to your boil wouldn't make a huge difference, but it would theoretically make your beer more bitter. There are a number of sites that can help you with the exact calculations, but each of them will give you a slightly different number. Either way, the longer you boil hops, the less aroma and more bitterness you'll get. That's why you normally add bittering hops towards the beginning of the boil and aroma hops towards the end.

Here are a couple calculators you can try:
http://www.rooftopbrew.net/ibu.php
http://www.hotv.org/tools/hopbitterness.html
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Old 05-01-2013, 03:37 AM   #7
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Thank you everyone for the replies. Will taka everything into consideration next brew .

Cheer 17

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Old 05-01-2013, 04:24 AM   #8
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Sounds like you hit all your numbers. If you want to beige accurate on SG you would need to measure volume in ounces not quarts.

When you have an accurate value for brew house efficiency you will be able to hit the parboil gravity and volume numbers

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