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Gravity post-mash vs gravity post boil not matching

bougie1st

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Hi all

Looking for advice please.  I have a Grainfather system, using BS2 for all my calculations (not the website calculator).  Doing this, I have been able to account quite accurately my losses at each stage of the process.  However, an issue that I keep having is that, after hitting my expected gravity post-mash, I seem to be ending up with less sugar in the final wort post-boil, and I can't figure out why.

For example, I just brewed a black IPA, target 12.5L into fermenter.  Expected post-mash gravity 1.045, achieved 1.046.  Pre-boil volume (measured) was 18.36L. Post-boil volume was 14.41L, with 3.95L/hr off (21%).  This is only my second half-sized batch, but my previous boiloff with the bigger volume was ~3.2L.  I'm expecting a little higher boiloff, due to a more vigorous boil.

So, using the tool in BS2, I should have a post-boil gravity of 1.059 (this is also what I get using my own calcs, C1V1=C2V2).  In fact, when I add in shinkage in BS2, I should have 1.061.  My actual measured was 1.052!

My measuring process - post mash, get wort up to boil, having stirred, take sample, stick in freezer until 20 deg then measure with hydrometer. Volume measured at the same time (it may result in a little higher gravity and less volume due to evaporation in the time to boil, but I figure it's probably not a lot).  Post boil gravity is sampled by hydrometer as it comes out of the counter flow chiller at 20 deg.

Any ideas as to why this is happening would be greatly appreciated.  It has been happening with the larger volume boils too, so it isn't a 'half batch' issue.  I have absolutely no idea where I am going wrong
 
Greetings bougie1st - I must admit, I am not at all familiar with the grainfather system and your comments/question are rather confusing to me.  So, my suggestion is to post your reciep(s) so they can be downloaded and looked at by members in this forum.  Posting the recipe will include the mash and equipment profiles.

Also, I can tell you that many of the brewers who own the grainfather system have many questions related to efficiency and setting up BS2 to suit their brewing style.  So, my second suggestion (if you haven't already done so) is to use the search feature in this forum.  You may find your question(s) have already been answered.  If not, post your recipes and lets have a look.  ;)
 
Thanks, KellerBrauer.  Please find beerXML file attached.

This isn't really an equipment set-up question (I don't think, anyway).  I seem to have all that under control.  It's that the amount of sugar I have before the boil doesn't seem to match what I am measuring at the end.  My mash efficiency seems to be good, and the boil off rate seems to be as expected, but the post-boil wort doesn't seem to be as concentrated as I'd expect (or as BS2 expects) for the amount of water evaporated off.

I must be doing something wrong, but I don't know what.

Thanks again
 

Attachments

  • Black IPA.xml
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OK, I've looked through your recipe and have a couple of questions. [forgive me as I don't have a Grainfather so some of these questions may be due to the lack of understanding of that particular device)

What was your final volume into the fermenter?  Did you actually end up with 2.5 liters of trub and loss?  (It would help in the future if you filled out those values in the 'sessions' tab)

How are you measuring your volumes and are you sure they are correct? 

Just as a note, I always pull a sample of the wort for gravity measurement as the wort is heading to a boil.  That way if I missed my target, I can alter the boil time to compensate.

For your post boil gravity, is it possible that the sample you pulled from your chiller did not represent the bulk of the wort produced?  I don't know how well mixed the wort remains inside the grainfather once the boil has concluded.

 
Greetings bougie1st - a couple issues come to view as I look at the recipe you attached.  I'm guessing the majority of your concerns and inaccuracy stem from your measurements.  First, I don't believe its possible to achieve a Brewhouse Efficiency of 106.5% and a Mash Efficiency of 102.4%.  So I think you need to look at the method in which you are taking hydrometer readings.

First, a hydrometer is typically calibrated at 60 degrees F.  You can check the calibration by dropping it into 60 degree distilled water - the reading should be zero.  If its not, discard your hydrometer and get another one.  So, now to check the wort, I drop my hydrometer into my testing tube filled 3/4 with wort and take a reading.  Then I immediately drop in a thermometer to take a temperature reading.  I then enter the two readings into the Hydrometer Adjust Tool in BS2 and record the actual reading.  I think, perhaps, some accuracy is getting lost in your measurement process.

Also, according to the information entered in the Session Tab, the Estimated OG is 1.053 and the Measured is 1.052.  Now I'm confused.  Your original post indicated your OG was off by 11 points.

bougie1st said:
So, using the tool in BS2, I should have a post-boil gravity of 1.059 (this is also what I get using my own calcs, C1V1=C2V2).  In fact, when I add in shinkage in BS2, I should have 1.061.  My actual measured was 1.052!

To have the OG differ from the estimated by .001 is not out of the ordinary.  Lets face it, it is "Estimated" after all.

I hope this information helps.

Good Luck!!
 

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    Edited.jpg
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Hmmm. Not sure what happened with that file - that is not my actual details in BS2.  My BH Eff is set at 76% and measured was 70.3%.  I will try this file thing again, but as a BS2 file instead.  It doesn't seem to have accurately included my data in that file.

KellerBrauer said:
Greetings bougie1st - a couple issues come to view as I look at the recipe you attached.  I'm guessing the majority of your concerns and inaccuracy stem from your measurements.  First, I don't believe its possible to achieve a Brewhouse Efficiency of 106.5% and a Mash Efficiency of 102.4%. 

I agree with you - that is impossible.  I'm sorry that that file didn't have the correct info in it.  I'm not sure why it exported like that.  It seems to have the accurate data in the BS2 file now.

KellerBrauer said:
You can check the calibration by dropping it into 60 degree distilled water - the reading should be zero.  If its not, discard your hydrometer and get another one. 

Mine is calibrated at 20 deg C.  I have checked this before and all was ok.  Have just done so again now, and it measures 1.000.  Also, I triple checked the temp, using my standard thermometer, and comparing it to the GF controller thermometers (the new controller and my older, original, one).  All say 20 deg.


KellerBrauer said:
So, now to check the wort, I drop my hydrometer into my testing tube filled 3/4 with wort and take a reading.  Then I immediately drop in a thermometer to take a temperature reading.  I then enter the two readings into the Hydrometer Adjust Tool in BS2 and record the actual reading.  I think, perhaps, some accuracy is getting lost in your measurement process.

For pre-boil, I take the wort as it gets to the boil, meaning that I have stirred it a lot (for hot break), and the agitation of the boiling should mix it.  I then cool that to 20 deg and then measure it at that point, so there is no conversion for temperature differences, trying to increase my accuracy.

Oginme said:
OK, I've looked through your recipe and have a couple of questions. [forgive me as I don't have a Grainfather so some of these questions may be due to the lack of understanding of that particular device)

What was your final volume into the fermenter?  Did you actually end up with 2.5 liters of trub and loss?  (It would help in the future if you filled out those values in the 'sessions' tab)

I had 1.33L trub loss.  Again, sorry that the file was incorrect.  I don't know why it didn't carry over the accurate details

Oginme said:
How are you measuring your volumes and are you sure they are correct? 

I measure the height of the wort, frequently from the top down, and convert that to the volume using a spreadsheet.  I have attached the sheet for the related brew.  You'll see at the top that I measure it going in, and then I measure from the top before starting to make sure that it is accurate either way.  I have done quite a few brews with this now, and it seems accurate enough.  The data in column L across is to allow me to compare my values to BS2 so that I can identify where I my assumptions need more dialling in.  As this brew is still fermenting, I haven't finished all the data in this spreadsheet. I also have a page that I enter things like grain absorption, boil-off etc, to calculate the average and then enter it into BS2.  Please note, I am not following the GF calculations, but rather am treating my equipment like any other and adjusting the calculations in BS2 based on my experience.

Oginme said:
Just as a note, I always pull a sample of the wort for gravity measurement as the wort is heading to a boil.  That way if I missed my target, I can alter the boil time to compensate.

Me too - as noted above

Oginme said:
For your post boil gravity, is it possible that the sample you pulled from your chiller did not represent the bulk of the wort produced?  I don't know how well mixed the wort remains inside the grainfather once the boil has concluded.

This should be ok.  I do a proper whirlpool for 5 minutes to get a good trub cone and help with pumping the wort out.  It should therefore be well mixed.  I catch a sample from the cooled wort out of the chiller as it is going into the fermenter, usually at a random point, but not until I know the temp is a stable 20 deg C on my thrumometer.

I'm sure this will be something simple that I am missing, but am still scratching my head here.  I thought it might be some water left in the tube for testing (after cleaning from previous samples) causing some dilution, but I now thoroughly dry it before taking another sample.

Sorry for the inaccurate file.  This seems to be right now as a BS2 file

Thanks again
 

Attachments

  • BYO Black IPA.bsmx
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  • BYO Black IPA Calculator.xlsx
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Greetings bougie1st - I have reviewed both of the documents you've posted with a focus on the BS2 file and frankly, I don't see anything of any startling concern.  The measured Post Mash and Pre-Boil are 1.002 away from Estimated and the measured OG is 1.004 away from Estimated.  You collected 0.2 gallons more extract than estimated, so a slightly longer boil time might be in order and that's why the  Measured OG is slightly lower than the estimated.  Again, I don't see any issues with the numbers in BS2.

However, I did not pay a lot of attention to the spreadsheet.  My only comment in that regard is it seem you might be trying to reconcile the numbers between the two calculating tools and that aspect in itself is prone to error.  My suggestion is to utilize and trust one calculation tool and one only.

Perhaps Oginme can see something I missed, but I'm at a loss.

Good luck and I hope the end result is a fine beer!!  ;)
 
Something I would recommend doing for your volume measurements is to make a dip stick by filling your kettle with measured amounts of water and marking a dip stick at each interval.  I fought my measurements of volume for a couple of brews when I purchased a new boil kettle a few years ago.  One of the constant errors which I encountered was the measurement of the first liter into the pot was not proportional to the diameter/height of the pot due the internal radius of the pot where the bottom transitions to the side wall.  Depending upon that radius, the volumetric reading can differ from that of a straight cylinder by a significant margin.  For me it threw my volumes off by 0.22 liters (very gentle transition), a ~2% error for a 10 liter batch with 1 liter of trub.  While this may not seem like a lot, it meant that my volumes of wort were always a bit short versus what I had predicted and measured.

I don't know how much this is on a grainfather nor if any other intrusions for valves or ports inside the vessel may impact the volume to depth ratio versus that of a cylinder, but it may be worth checking out.
 
Thanks again for your advice.  I'm glad to see that I'm not too far off.

Maybe it is just a cumulation of a few errors.  While the gravity is out only a little from the predicted, it is still out when looking at the actual numbers.  I overshot the mash gravity, so with the boil-off, I should still be greater than predicted, which the BS2 boil-off tool indicates.  It could be that I there was a measurement error in the mash gravity (too high) then an error with the volume (too low), making it look like there is more extract originally, then the volume error compounds that, so when the number comes in low at the end, it seems worse than it is.

I'm taking your advice, Oginme, and marking a dipstick right now.

Thanks again for your time.  That spreadsheet is complicated, and I'd love to give it away, but BS2 doesn't allow you to enter your exact measurements at each step, nor does it generate a report to show you where you are off.  As it stands, the dialling in part is a little bit of guess work - ie I think the grain absorption is x. If the information could be entered at each stage, and a report generated showing the differences and average values of your brews with a piece of equipment, then the spreadsheet would be unnecessary.  I'll pop this into suggestions and see what Brad thinks of it.
 
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