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Old 12-26-2012, 11:51 PM   #1
Scottyh
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Default Gravity Readings with my Brewing Process

Hi, I just did my third all-grain yesterday and was hoping to get some input on my process and specifically with the gravity readings I took yesterday since I am totally confused. I am using the BIAB method. I had developed my recipe using Beersmith and used about a gallon less water for the mash than what the original recipe called for (my RO tank at home was empty and did not want to wait for another hour for it to fill up again). So I did my mash and think I hit my temperatures pretty well. After the mash I added about a gallon of water to get to my pre-boil water volume. After mixing the new water in I then took a gravity reading which was 1.034. Beersmith estimated the pre-boil gravity would be 1.050 so I thought I was in alot of trouble. I went ahead anyways and did the boil, cooled the wort and put it into the fermenter. I then added the yeast and then took the OG measure which was 1.055. Beersmith had the estimated OG at 1.056 so I guess I am OK? I could not find any previous threads on this so I if anyone has some input as to why the pre-boil gravity was so off but the measured OG looks OK? Thanks in advance!

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Old 12-27-2012, 12:21 AM   #2
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There's a couple of things that could attribute to this that I can think of...
1) the water temp. You said you took a reading pre-boil and I'm assuming post mash then the temp would definitely be a factor. Hydrometers are calibrated to be used at 68 degrees (I could be a couple of degrees off, but its close to there)
2) the boil off. If you boiled off enough water and it became concentrated enough its possible to change the gravity. Although I don't actually know how much water it would mean that you had to boil off.

*insert someones math work here*

Actually, there could be another issue. The crush of the grain, if the crush was to coarse its possible to affect your gravity significantly

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Old 12-27-2012, 12:40 AM   #3
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ok thanks for the reply. Should I be waiting for post mash to cool before taking the gravity reading?

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Old 12-27-2012, 02:49 PM   #4
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That's what I would recommend, taking the gravity is one of the last things I do before actually transferring to a fermentor.

Upon doing a little research, hydrometers are either calibrated for 68 or 60 degrees (F).

http://www.brewersfriend.com/hydrometer-temp/

It seems like yours is calibrated for 60 degrees. By using the numbers you mentioned and if it was post mash pre boil I imagine the temperature then would have been between 150-160 degrees. So if you type that in for the temp, along with your actually gravity (1.034) you'll notice that in reality your gravity was exactly around what it should have been (1.050-1.055). : )

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Old 12-27-2012, 02:55 PM   #5
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Quote:
Originally Posted by Scottyh View Post
Hi, I just did my third all-grain yesterday and was hoping to get some input on my process and specifically with the gravity readings I took yesterday since I am totally confused. I am using the BIAB method. I had developed my recipe using Beersmith and used about a gallon less water for the mash than what the original recipe called for (my RO tank at home was empty and did not want to wait for another hour for it to fill up again). So I did my mash and think I hit my temperatures pretty well. After the mash I added about a gallon of water to get to my pre-boil water volume. After mixing the new water in I then took a gravity reading which was 1.034. Beersmith estimated the pre-boil gravity would be 1.050 so I thought I was in alot of trouble. I went ahead anyways and did the boil, cooled the wort and put it into the fermenter. I then added the yeast and then took the OG measure which was 1.055. Beersmith had the estimated OG at 1.056 so I guess I am OK? I could not find any previous threads on this so I if anyone has some input as to why the pre-boil gravity was so off but the measured OG looks OK? Thanks in advance!
Right there is the problem. Wort is much denser than water and it is quite difficult to get them to mix properly. You just measured more water than wort. It could have gone the other way too and had you measuring more wort than water and gotten a much higher OG than planned.
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Old 12-27-2012, 06:56 PM   #6
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Originally Posted by RM-MN View Post
Right there is the problem. Wort is much denser than water and it is quite difficult to get them to mix properly. You just measured more water than wort. It could have gone the other way too and had you measuring more wort than water and gotten a much higher OG than planned.
Stratification can cause some measurement error, but I'm not sure about it causing a 16 point difference in a 1.054 wort. Mr. Wizard from BYO talks about almost this exact topic it in this article:
http://byo.com/stories/wizard/articl...ling-mr-wizard
(scroll down to the second question)

And he's talking about mixing LME with top off water. (LME has a specific gravity of about 1.300)

to quote the wizard:
Quote:
The variation is typically between 0.1–0.2° Plato or about 0.0004–0.0008 specific gravity units.
Temperature is fairly likely. at 160 degrees the reading will be about 15 points which is what the OP was seeing.
http://www.ebrew.com/primarynews/ct_...correction.htm
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Old 12-28-2012, 04:07 AM   #7
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Also, make sure your equipment profile in BeerSmith is as accurate as you can get it. All of the volumes use your equipment profile so it needs to be accurate.

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