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Home Brew Forums > Home Brewing Beer > All Grain & Partial Mash Brewing > how do you take pre-boil gravity readings?
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Old 02-16-2010, 06:26 AM   #1
lpdb185
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Default how do you take pre-boil gravity readings?

i'm trying to think of everything i can for my first AG attempt. as i understand it, i need to get gravity readings from each of the 3 runnings from my mash tun (i plan on using Bobby_M's double batch sparge method) and one overall pre-boil sample. what are some of your methods of doing this? do you pull a sample and immediately take a reading with hydrometer (assuming it will not shatter)? or do you draw a sample, let it cool, then take a reading? i'm sure it doesn't matter for the sake of calculation, but i'm really wondering how you fine folks do this in order to be most efficient with your brewing time.

i've heard of people using temperature corrections for gravity readings, so i'm assuming i am supposed to take the gravity reading while the wort is still at mash temp. if that's correct, where can i find a temp correction guide/tutorial/spreadsheet? or, is this something that Beersmith will do for me?


thanks for your help

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Old 02-16-2010, 06:43 AM   #2
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I will pull a sample after I vorlauf each time, & then stick it in the freezer to cool it quickly. I won't take a gravity reading until it's below 100, then I will use temp corrections. There is a table in How to Brew that gives you corrections, page 264 & 265 of the hardcopy. I don't use brewing software, so I'm not sure about beersmith.

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Old 02-16-2010, 06:53 AM   #3
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You will have to get all of your runnings into the kettle and mix WELL before you attempt a preboil reading. I draw some off into my measurement cylinder and put it in the freezer to cool it down to at least 80 F then take a reading and correct for temp.

Of course if you had a refractometer you wouldn't have to worry about the cooling.

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Old 02-16-2010, 12:46 PM   #4
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Default cooling wort sample

float a small mixing bowl in a pot or bowl filled with ice water. I used a pie plate in a big mixing bowl filled with ice. I filled my (plastic) hydrometer flask to the desired level, dumped it into the dry(!) pie tin, swirled it with a spoon for 15-20 seconds: 63F.

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Old 02-16-2010, 12:56 PM   #5
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I use this: http://hbd.org/cgi-bin/recipator/rec...ydrometer.html

Basically I use my measuring jug to pull about 100 mL, let it cool a bit then pour it into my hydrometer vessel with a glass stick thermometer. Get temp reading, drop in hydrometer and make calculations. Because it's pre boil, the sample can go back into the kettle.

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Old 02-16-2010, 02:22 PM   #6
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Refractometer. You can get one on Ebay pretty cheap.

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Old 02-16-2010, 02:46 PM   #7
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Quote:
Originally Posted by lpdb185 View Post
i'm trying to think of everything i can for my first AG attempt. as i understand it, i need to get gravity readings from each of the 3 runnings from my mash tun (i plan on using Bobby_M's double batch sparge method) and one overall pre-boil sample. what are some of your methods of doing this? do you pull a sample and immediately take a reading with hydrometer (assuming it will not shatter)? or do you draw a sample, let it cool, then take a reading? i'm sure it doesn't matter for the sake of calculation, but i'm really wondering how you fine folks do this in order to be most efficient with your brewing time.

i've heard of people using temperature corrections for gravity readings, so i'm assuming i am supposed to take the gravity reading while the wort is still at mash temp. if that's correct, where can i find a temp correction guide/tutorial/spreadsheet? or, is this something that Beersmith will do for me?


thanks for your help
I batch sparge and used to take a sample from the 1st, 2nd, and 3rd runnings (I boil 13.5 gal for a 11 gal post boil batch) but I never used the data collected for any purpose. Now I just take a sample pre and post boil. Pre boil sample comes out of the kettle at sparge temperature and I just let it cool to room temperature. Post boil is taken after cooling and whirlpool before draining to fermenter. The actual hydrometer measure takes place last thing when all clean up is done which is usually 4 -5 hours after pre boil sample is taken. All I calculate is brew house efficiency and a baseline to measure attenuation after fermenation is done.

I don't bother pulling samples to determine when the beer is done if my blowoff tube displays "normal" rate of CO2 discharge during active phase. I let it stay in fermenter for 2 weeks, pull a sample to measure attenuation and keg it up.
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Old 02-16-2010, 05:59 PM   #8
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Yes, beersmith does have a hydrometer correction tool that lets you put in your temp and measured gravity and it converts it.

I usually draw off the wort, stick my thermometer in to get a temp, take the gravity reading, then take the temp again. I average out the temps to use as the temp the gravity was read at and then plug that into beersmith.

I haven't had a problem with cracking the hydrometer. As long as you don't move it from really warm wort (150 degrees) and then rinse it off with 40 degree tap water you should be fine. I usually rinse it off with hot water from my tap and its never an issue.

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Old 02-16-2010, 07:17 PM   #9
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I would just take one reading after sparge is finished. Cool it to 60 and that will be the pre-boil. You can get your efficiency from this if you have carefully measured your volumes.

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Old 02-16-2010, 08:30 PM   #10
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wow, thanks for all the input. i thought i had read that you needed samples from each of the runnings, but never heard exactly why they needed to be split up like that. perhaps i'll just get the overall preboil gravity, like some of you say, and keep it simple. thanks for the link manticle.

if i decide to get a hydrometer, do i need to look for anything particular? are they all pretty much equal, or do i need to look for something specific? i ask because i breifly looked on the web and they are anywhere from $30 to $80.

thanks -

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