Author Topic: using gravity to keep track of boil off  (Read 1150 times)

Offline BrewQwest

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using gravity to keep track of boil off
« on: March 03, 2010, 10:16:16 AM »
Is it possible to keep track of your boil off (or the amount remaining in your kettle) taking various samples during the boil? Either by cooling the wort and using a hydrometer or by using a ATC refractometer? Won't the readings linearly increase as the boil off occurs so that you could compute your volume remaining?  This would hopefully prevent my erroneous readings using a stick skewed by bubbles from the boililng wort...
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Offline bluesman

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Re: using gravity to keep track of boil off
« Reply #1 on: March 03, 2010, 10:54:58 AM »
I like to sample the wort near the end of the boil to target the final gravity. I use a refractometer. I pull a sample into a dropper and usually take a couple of readings to see how repeatable they are due to evaporation. The sample should be applied to the prism and the cover plate should be closed quickly.
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Offline denny

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Re: using gravity to keep track of boil off
« Reply #2 on: March 03, 2010, 11:38:18 AM »
I like to sample the wort near the end of the boil to target the final gravity. I use a refractometer. I pull a sample into a dropper and usually take a couple of readings to see how repeatable they are due to evaporation. The sample should be applied to the prism and the cover plate should be closed quickly.

I do the same thing.  I aim for target gravity, not target volume....although ideally I hit both!  But it depends on what the OP wants to accomplish.  If he just wants to know when to quit boiling, then I'd say gravity is more important than volume.  But if he wants to track boiloff to figure his kettle volumes, then this method wouldn't work.
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Offline bluesman

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Re: using gravity to keep track of boil off
« Reply #3 on: March 03, 2010, 11:58:20 AM »
I like to sample the wort near the end of the boil to target the final gravity. I use a refractometer. I pull a sample into a dropper and usually take a couple of readings to see how repeatable they are due to evaporation. The sample should be applied to the prism and the cover plate should be closed quickly.

I do the same thing.  I aim for target gravity, not target volume....although ideally I hit both!  But it depends on what the OP wants to accomplish.  If he just wants to know when to quit boiling, then I'd say gravity is more important than volume.  But if he wants to track boiloff to figure his kettle volumes, then this method wouldn't work.

True...as far as gravity/volume ratio. He may want to make a water addition or boil longer depending on his target gravity if he's planning to target a gravity per volume ratio. I hope this helps.
Ron Price

Offline hokerer

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Re: using gravity to keep track of boil off
« Reply #4 on: March 03, 2010, 12:32:40 PM »
If he just wants to know when to quit boiling, then I'd say gravity is more important than volume.

Wouldn't that drive your hop schedule crazy, though?  If he gets to what he thought should be the end of his boil, checks gravity and realizes he needs to boil another, say, ten minutes, his 60-minute addition becomes a 70-minute addition.
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Offline bluesman

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Re: using gravity to keep track of boil off
« Reply #5 on: March 03, 2010, 12:34:28 PM »
If he just wants to know when to quit boiling, then I'd say gravity is more important than volume.

Wouldn't that drive your hop schedule crazy, though?  If he gets to what he thought should be the end of his boil, checks gravity and realizes he needs to boil another, say, ten minutes, his 60-minute addition becomes a 70-minute addition.

Good point. It's a dynamic situation.
Ron Price

Offline denny

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Re: using gravity to keep track of boil off
« Reply #6 on: March 03, 2010, 12:42:17 PM »
If he just wants to know when to quit boiling, then I'd say gravity is more important than volume.

Wouldn't that drive your hop schedule crazy, though?  If he gets to what he thought should be the end of his boil, checks gravity and realizes he needs to boil another, say, ten minutes, his 60-minute addition becomes a 70-minute addition.

There is so little change in hop utilization past 60 min. that you can kinda just forget about it.  I take a gravity reading about 20 min. from what I estimate to be the end of the boil and time my finishing hops accordingly.
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Offline babalu87

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Re: using gravity to keep track of boil off
« Reply #7 on: March 03, 2010, 01:01:00 PM »
If he just wants to know when to quit boiling, then I'd say gravity is more important than volume.

Wouldn't that drive your hop schedule crazy, though?  If he gets to what he thought should be the end of his boil, checks gravity and realizes he needs to boil another, say, ten minutes, his 60-minute addition becomes a 70-minute addition.

There is so little change in hop utilization past 60 min. that you can kinda just forget about it.  I take a gravity reading about 20 min. from what I estimate to be the end of the boil and time my finishing hops accordingly.

On a similar note do you think FWH can be boiled too long............. as in a 2 hour boil?
Jeff

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Offline denny

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Re: using gravity to keep track of boil off
« Reply #8 on: March 03, 2010, 01:02:50 PM »
On a similar note do you think FWH can be boiled too long............. as in a 2 hour boil?

Damn good question.  No direct experience, but I'd guess that the scenario you describe would be too long to retain the desired effects.
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Offline babalu87

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Re: using gravity to keep track of boil off
« Reply #9 on: March 03, 2010, 01:24:15 PM »
On a similar note do you think FWH can be boiled too long............. as in a 2 hour boil?

Damn good question.  No direct experience, but I'd guess that the scenario you describe would be too long to retain the desired effects.

In a few months I'll find out

I boil Baltic Porter for 2 hours and rather than do a 15 or 20 minute addition this year I went with FWH

I'm pretty sure at 90 minutes it doesnt make a lick of difference though. I have a Pils that was FWH with a late hop addition and to me its perfect, I need to send one to Kai to be sure  ;)
Jeff

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Offline denny

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Re: using gravity to keep track of boil off
« Reply #10 on: March 03, 2010, 01:46:37 PM »
Good point...I've done pils and other beers FWH with a 90 min. boil and it didn't seem to change the character of the FWH.
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Offline bluesman

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Re: using gravity to keep track of boil off
« Reply #11 on: March 03, 2010, 02:24:59 PM »
If he just wants to know when to quit boiling, then I'd say gravity is more important than volume.

Wouldn't that drive your hop schedule crazy, though?  If he gets to what he thought should be the end of his boil, checks gravity and realizes he needs to boil another, say, ten minutes, his 60-minute addition becomes a 70-minute addition.

There is so little change in hop utilization past 60 min. that you can kinda just forget about it.  I take a gravity reading about 20 min. from what I estimate to be the end of the boil and time my finishing hops accordingly.

But if he has flavor additions in at 20 and 30 min it will increase the total IBU'S somewhat. I guess we need specifics in order to nail down an exacting response.
Ron Price

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Re: using gravity to keep track of boil off
« Reply #12 on: March 03, 2010, 04:34:27 PM »
You can absolutely determine your volume based on gravity as long as you establish a base line ( volume and gravity)  before you start boiling.

Offline tubercle

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Re: using gravity to keep track of boil off
« Reply #13 on: March 03, 2010, 04:59:50 PM »
Is it possible to keep track of your boil off (or the amount remaining in your kettle) taking various samples during the boil? Either by cooling the wort and using a hydrometer or by using a ATC refractometer? Won't the readings linearly increase as the boil off occurs so that you could compute your volume remaining?  This would hopefully prevent my erroneous readings using a stick skewed by bubbles from the boililng wort...


  Dude,

  If your stick measurement is accurate but skewed by "bubbles for the boiling wort", cut down the fire and let the bubbles settle for a few and take your reading. Then, fire it back up if necessary. Your beer will be NO different if you want 5.25 gallons and you get 5.20 or 5.28 gallons.

  You are trying to take something very simple and trying to add infinite variables to it. Enjoy brewing. You should be lying awake at night thinking of your next recipe, not your next disaster.

  Not trying to be hard....just want you to enjoy life in general and brewing specifically, as I do. ;D
Sweet Caroline where the Sun rises over the deep blue sea and sets somewhere beyond Tennessee

Offline BrewQwest

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Re: using gravity to keep track of boil off
« Reply #14 on: March 04, 2010, 02:07:43 PM »
wow, thanks for all the responses everyone.  The Jan and Feb cold dry MN winter months really did a number on my boil offs (this is my first winter season as an outdoor all-grain brewer).. Normally I try to start with 7 to 7.5 gallons so as to end with about 5.5 to 6 in the kettle. Lately I have been coming up really short, so two batches ago I boiled 8 and ended with 4.25 and last batch I started with 9 and ended with 4.75... Being the newb that I am, I was hoping for a way to associate my intended OG with volume remaining in the kettle so that I could end the boil when the proper gravity/volume was reached... I hadn't thought of possibly upsetting the IBU profile if I quit boiling before the 55-60 minutes mark, so thank you for stating that....Also hadn't thought of just turning off the heat to take a reading and then turning it back on again....  :-[  ...  Guess I just go with 9.5 preboil next time in order to hopefully hit my 5.5 to 6 remaining.  Shouldn't I be able to track the boil off by computing
preboil BRIX multiplied by preboil Volume which will give me preboil gravity units.  15 minutes into the boil I should be able to take another BRIX reading and divide those preboil gravity units by my new BRIX reading to give me the new remaining Volume... But as someone earlier said, it is impossible to cut short the boil if you have late hop additions going in..... So even after I know the exact point when my volume and gravity had been reached, there would be nothing to do about it until after the boil had run its time limit anyway...Hhhmmmmm....
On a never-ending journey for the perfect pint of beer...