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Gravity readings

davidrgreen

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Just wondering at what different stages do you all measure your gravity?

I have been measuring preboil, post boil and then after fermentation...  which do you think are the most important, post boil and after fermentation?
I presume preboil is purely for efficiency, post boil and after fermentation is for alcohol percentage, is this correct?
 
Correct - ish.  After fermentation, I look at it after primary to see that the yeast is mostly done, then into a secondary to finish off.  Then I measure the final at kegging / bottling time to get the actual %.
 
Pre-boil to post-boil is all about efficiency, but you can (and should) use it as a diagnostic tool to figure out where problems exist in your setup or how to maximize that efficiency. For example, if your pre-boil gravities are low, you might be able to ascertain that you're sparging too much, or that your mash temperatures might be off and you're not getting good or complete conversion. If your post-boil gravities are low, but pre-boil was right on, you might not have boiled off enough, or if post-boil is high, you might have boiled off too much.

I know of a couple brewers who don't bother with gravity readings anywhere during the process; they are content that they make beer :) Bottom line is that you can brew without taking a reading, by taking lots of readings, or somewhere in between. It's all about how much data you want out of your brewing process, and whether you want to do anything with it.
 
I measure pre-boil, post boil (when I put it into the fermenting tank), after primary, and after secondary.
 
Much of when you measure depends upon how you brew.  I do BIAB with a batch sparge, so I measure volume and gravity from the mash and the sparge.  Then I measure the volume and gravity of the combined wort pre- and post boil.  Lastly, a measurement into the fermentor and post fermentation.

The main reason I do the mash and sparge separately is a check on the efficiency of each and, when combined, they should add up to be equivalent to by pre-boil numbers.  It gives me a check on the process before I spend time scratching my head (or other parts) wondering what might have gone wrong.
 
Oginme said:
The main reason I do the mash and sparge separately is a check on the efficiency of each and, when combined, they should add up to be equivalent to by pre-boil numbers.  It gives me a check on the process before I spend time scratching my head (or other parts) wondering what might have gone wrong.

This isn't a bad idea.  I may have to try this next time.
 
A pre-boil measurement can certainly help diagnose process problems, but more immediately, it tells you if you need to boil longer or dilute to hit your target OG.

I think there's a federal regulation that mandates checking gravity every couple of days starting about a week into fermentation.
 
Obviously the temperature will be totally different to what the hydrometer is calibrated to... do you check it while its hot and do the thermal adjustments or do you wait until its cool?
Just wondering if the hydrometer will be ok with the hot liquid?
I usually try to cool first but have wondered about using it in the hot wort...
 
I do the checks on the mash and sparge with a refractometer.  The pre-boil I use both the refractometer and a hydrometer sample which has been cooled in the fridge (usually works out that I get the reading about 20 minutes after the boil has started).  Post boil is checked with the refractometer and the cooled wort into the fermentor is checked with both refractometer and hydrometer.  Taking the dual measurements with the refractometer and hydrometer also helps to ward off any problems with calibration.

Can you tell I spent too many years as a process control engineer?  I like to collect the readings but don't trust any one source...
 
I check it before I pitch the yeast to learn what kind of efficiency I got off the grain, and again before it goes into the keg to learn how potent it is.
 
Refractometer, all during sparge and boil, as everyone else said, and I do "auto-correct" if I'm off for some reason.  I try to get the beer within two SG points of the target. 

I also test the final runnings to see how low they are, b/c I collect the first couple quarts for canning for yeast starters.  (I either add DME to get to 1.030 or add leftover boiled wort later.) 

For those with refractometers, Walmart sells these s/s condiment cups at 4/$1, and if you put some drops of wort in them, and the cup in a bowl with some ice water in it, the sample is ready to test within seconds on the refractometer.  I just dip the long s/s spoon in  there twice and drip it into the cup.  Ice it and test it. 

http://www.walmart.com/ip/Mainstays-Condiment-Cups/14964954
 
davidrgreen said:
Obviously the temperature will be totally different to what the hydrometer is calibrated to... do you check it while its hot and do the thermal adjustments or do you wait until its cool?
Just wondering if the hydrometer will be ok with the hot liquid?
I usually try to cool first but have wondered about using it in the hot wort...

There is a tool for this!  :)  I use the tool in beersmith to adjust for the temp, since all I have is a hydrometer.  Would like to have a refractometer, but there are other things I want first, like a grain mill...
 
Hydrometers are calibrated @ 60 degrees F. Use 60 degree distilled water to check. This will be your accurate reading temp. Just cool your testing cylinder in cold ice water. As far as refractometers, make sure you have a temperature compensating model. Just a dip in with your metal stirring spoon,  a little blowing action is sufficient to cool your wort , and drip some on your refractometer.
 
OK, here goes:

1.  Mash - I start measuring at the 45 minute mark to check for progress.  As conversion progresses the gravity of the mash increases.  This reading gives me an early indication as to whether I'm going to be high or low.  I know the expected ratio of gravity between first and second runnings.  So, I can immediately tell when conversion has reached the desired point. 

2.  First runnings - I batch sparge in two batches of equal size (generally 4.04 gallons each).  I take temp, gravity, and volume measurements of each set of runnings. 

3.  Second runnings - as I said above, I know what this should be based on expected preboil Gravity. 

4.  Pre-boil - so I can make any adjustments for gravity, boil-off, or hops.

5.  I take 4-6 readings during the boil.  This allows me to monitor boil-off and accurately predict the total boil-time.  This allows me to ensure that my hop additions enter the wort with the correct remaining time.  This way I end up with the final wort gravity expected, and the hops have been in exactly the right duration. 

6.  Post-boil before I start the chiller.

7.  Post-chill before transferring to fermenter.

8.  After pitching yeast starter.  The starter will dillute the gravity a tad.

9.  Every day during the ferment.

10.  After transfer to the keg.

NOTE: I take volume, temperature, and gravity measurements at every point I can.  I calculate total points at every step on the hot side.  I write down the raw measurements and THEN I correct for any temperature curve (volume, hydrometer).  That way, if I screw up the math, I have the original data to rework from.  I cross-check all measurements against previous measurements and re-do if something doesn't make sense. 
 
All that effort payin' off?


I measure pre/post boil only. Losing interest in that because it's becoming more predictable and I don't make adjustments anyways.
 
grathan said:
All that effort payin' off?
I measure pre/post boil only. Losing interest in that because it's becoming more predictable and I don't make adjustments anyways.

Tom doesn't need me to speak for him, but what he's outlined is a series of control points that ensure true predictability in the balance of the finished beer. That's a very professional methodology.

My reading schedule is irrelevant for this thread, but we measure during recirculation looking for a peak starting gravity (22 to 26 Plato, usually). Then at several points during the sparge, especially once we're under 5 Plato (about 1.020) because it drops one degree for each barrel.

Yet, we've been caught by surprise and gotten all of our sugar out long before sparge is finished. Without similar control points like Tom outlined, we'd have oversparged and come in way under gravity. That's especially problematic because a normal sparge gives us 92 to 95% mash efficiency.

 
brewfun said:
we'd have oversparged and come in way under gravity. That's especially problematic because a normal sparge gives us 92 to 95% mash efficiency.

That's a whole new topic that might benefit new brewers.  OVER-sparging that reduces the gravity.  Many don't understand the dilution that occurs toward the end of sparging. 
 
grathan said:
All that effort payin' off?


I measure pre/post boil only. Losing interest in that because it's becoming more predictable and I don't make adjustments anyways.

In short, yes.  Its a bit of a long explanation as to HOW...but, if people are interested I can compose a series of replies explaining how I use the readings to CONTROL my processes.  I don't just take the readings for fun.  I DO actually manipulate the process throughout the brewday (and fermentation) to ensure that I end up with the beer I expected to make. 

I manage the mash, the sparge, the boil, and the ferment via these readings.  I have procedures for tweaking each of these steps based on the readings that I take.  I'm happy to elaborate, if people are so inclined.
 
I have to say welcome back Tom to.

I would definitely like  you to elaborate on the subject. Always more to learn about brewing.
 
tom_hampton said:
In short, yes.  Its a bit of a long explanation as to HOW...but, if people are interested I can compose a series of replies explaining how I use the readings to CONTROL my processes.

Hi Tom, nice to see you active again on the BS-forum!
I would like to improve my process control/reproducibility and I am interested to learn how you use your readings to control your processes. I am also interested in when and especially how you take your readings. I've seen some examples on the BS-forum where colleague members think they take the same readings or measurements, but they experience different results because they did it in a different way. Related to this perhaps some practical tips "what to avoid".
I am sure other members are interested as well.
Regards,
Slurk
 
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