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Estimated/measured pre-boil gravity different, but estimated/measured OG the sam

mightyhor

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At the weekend I did a brew based on the same BeerSmith mobile equipement profile I have been using for a long time, and which has served me well. I haven't used it in over a year, but as far as I can recall I stopped taking pre-boil gravity readings as I always hit my OG and never changed my basic technique. All readings taken at the correct temperature BTW!

As I was reminding myself of the process I did take a pre-boil reading and it was a lot lower than expected ? 1.029 not 1.039.
Changing efficiency in BeerSmith from 77% to 62% made this correct, allowing me to adjust the hop schedule/bitterness (OG now 1.046 not 1.054).

I hit the predicted OG perfectly, but the post-boil volume turned out to be 47l not 40l, and changing the batch volume in BrewSmith meant that the automatic boil volume was correctly predicted (prior to this I had been overriding it), but it also meant that the efficiency needed to be raised back to 77% to get the correct OG (1.046)!

However, this now this means that the predicted pre-boil gravity is back to being too high (1.039 rather than the measured 1.029), so I would have encounterd the same problem measuring the pre-boil gravity as before.

Therefore, efficiency of 62% gets correct pre-boil gravity but 77% gets correct post-boil gravity. Why the anomoly?

I have a 45l mash tun, which is dialled into BeerSmith, and I mash/mash out/sparge with enough water to get a pre-boil volume of 60l (so with this recipe, with 9kg of grain, I used a total of 69l or water).

Am I doing something wrong in BeerSmith such that it doesn't realise that I'm using a lot more water prior to the boil, and therefore thinks that the pre-boil gravity should be higher? I have tried increasing the mash tun volume to 69l to match the actual mash/sparge water volume used, but it makes little difference.

The pre-boil volume, boil off rate, shrinkage, trub loss etc. all seem to be correct, so I also can't understand why the predicted OG of 1.046 is achieved even when the pre-boil gravity is so far off.

Any help greatly appreciated!
 
This discrepancy between the volume and gravity measurements indicates that your equipment profile and brew house efficiency are not properly represented by the figures in the current profile. 

There are two material balances represented in the software.  The first is the volume balance which is set by the batch size and controlled using the process losses within the equipment profile and grain absorption figures.  To get this to better represent your process, it is important to take good, accurate readings of your water inputs, wort collected from the mash, post boil volume, and losses in your mash tun, pumps and lines, and trub after filling the fermenter.  There are several tutorials for this in Brad's blogs and videos on YouTube which you can search for by typing in 'BeerSmith' and 'Equipment profile' into the search bar on YouTube.

The second balance is the amount of sugars which get extracted from the grain and end up in the fermenter and is designated 'brew house efficiency (BHE)'.  This expresses the percentage of the sugar potential available from the grain bill.  BeerSmith takes this figure and applies it to the grain bill to determine how much of that sugar goes to make up your gravity reading.  It then uses the volume balance to calculate all additional losses of sugar throughout the process to arrive at the mash efficiency or how much sugar makes up the initial wort collected from the grains.

My advice is to set your efficiency back to your original value and to use your next brew (unless you have really good notes on volumes for this last brew) to calculate the process losses designated in the equipment profile.  Only then will you be able to have confidence in the calculated BHE from BeerSmith to set the value there to represent your process properly.

One thing to note:  I have found in the few kettles and fermenters that I have which are pre-marked with volume indicators that these marking can often be misleading and significantly affect your ability to get the volumes to match consistently.  I recommend making a measuring stick or remarking the vessels based upon actual measured volumes to give yourself the best accuracy in measurements.

As you go through this, if you need help or guidance on calculations, we are here to help.
 
Hi,
Thanks for your response.

The water volumes going in are very precise, and I calculate my mash/mash out/sparge volumes separately from Brewsmith. I am 100% sure that 69l were used for 9kg of grain, which give or take a small loss in the mash tun makes a 60l pre-boil volume.

Given that I ended up with 47l in the fermenters I have inputted the 13l difference using boil-off, trub loss, etc.

The problem still remains ? why is the pre-boil gravity 1.010 lower than predicted when the OG is exactly as predicted?

Surely even if there were issues with extracting sugars there would be a very predictable move from pre-boil gravity to post-boil gravity? Or is this to do with there being a massive difference between the mash efficiency and the brewhouse efficiency?

If it's the latter, then I can't see how you would account for this, as there is only one parameter where you can enter efficiency.

 
If you calculate the volumes outside of BeerSmith, and have not 'dialed in' your equipment profile to do those calculations for you, then that is part of the issue.  If you want the program to give you good estimates of the gravity readings then that relies upon an accurate volume balance within the program.  The sugar extraction as measured by pre-boil gravity is linked to the volumes throughout the process.  This is why there is a difference between the mash efficiency and brew house efficiency.  The estimate of mash efficiency relies on the accurate calculation of process losses of sugar, which is quantified by the volume losses.

Approaching your gravity reading from a different direction, at what temperature did you take the pre-boil gravity reading?  Did you correct for thermal expansion affects on the gravity?
 
Just to clarify, as mentioned in the OP I'm using BeerSmith mobile and all gravity measures are taken at the correct temperature (20?C).

Is it possible to calculate these volmes using this software? In my mash profile the mash in and mash out volumes are correct, and I have checked drain mash tun and fill 100% ? the estimated pre-boil gravity is still the same.

Going back to my previous post though, surely the move from pre-boil gravity to post-boil gravity is very predictable? If I know the pre-boil gravity with accuracy and know the boiling losses, then the OG should follow from that, but it's much higher than BeerSmith predicts.
 
mightyhor said:
The problem still remains ? why is the pre-boil gravity 1.010 lower than predicted when the OG is exactly as predicted?

Surely even if there were issues with extracting sugars there would be a very predictable move from pre-boil gravity to post-boil gravity? Or is this to do with there being a massive difference between the mash efficiency and the brewhouse efficiency?

The issue may be in what you're considering a batch size. BeerSmith is stating the amount of sugar that gets to the fermenter. You've stated what's in the kettle post boil. The difference between the two is in your loss to trub & chiller.

In your original post, you stated 47l was your post boil volume, but the reply said that was in your fermenter. It's an important distinction because it changes your BHE.

Secondly, there is a difference between what your two gravity to volume ratios produce, when they should be identical. The  pre boil number of 1.029 in 60l produces 1740 gravity points (29 * 60 = 1740) Your post boil number is 46 * 47 = 2162. If the two were matched, you either had a pre boil gravity at 1.036 (your prediction) or a post boil gravity of 1.037 (not your measurement)

Generally, most brewers most accurately measure fermenter volume and gravity. So, let's go with your post boil numbers, shall we? That means the efficiency discrepancy is in your loss to trub & chiller. This is where sugar gets left behind, decreasing BHE. If you didn't leave any behind, then your higher BHE number is correct.
 
brewfun said:
Secondly, there is a difference between what your two gravity to volume ratios produce, when they should be identical.

Thanks for the technical way of phrasing it, this is exactly the issue ? why the discrepancy? Getting a perfectly accurate BHF wouldn't change the fact that the gravity to volume ratios should be identical.

The boil, chlller and trub losses are all dialed into BeerSmith and I am measuring the fermenter volume and gravity (which is presumably what BeerSmith estimates, as that's what you work with when fermenting, bottling etc.).
 
mightyhor said:
Thanks for the technical way of phrasing it, this is exactly the issue. why the discrepancy? Getting a perfectly accurate BHF wouldn't change the fact that the gravity to volume ratios should be identical.

The boil, chlller and trub losses are all dialed into BeerSmith and I am measuring the fermenter volume and gravity (which is presumably what BeerSmith estimates, as that's what you work with when fermenting, bottling etc.).

At this point, you should post your recipe as a .bsmx file so we can look over all of your parameters. Oginme and myself use this program regularly (me almost daily) across several sized systems and experience correct predictions.

Could any of these statements be true:

Your pre boil gravity measurement was actually warmer than you thought, causing a lower reading.

Your hydrometer is calibrated for 15C not 20C.

If you got 47l in the fermenter at exactly the predicted gravity, then you had zero trub.

If you got 47l in the fermenter, plus had trub, then the preboil volume would actually be increased to match your gravity reading.

Pre boil volume should be measured and calculated as hot (near boiling if shrinkage is set at 4%).





 
Thanks. How do I download in that format? It only seems to download in a .docx format from the website.

The answer to the first two statements is 'false'. The final three statements are a little confusing, and I'm not clear why these variables would affect the gravity to volume ratios so drastically.

The measurements were taken from the fermenter at 20?C, and there was trub in the kettle that was accounted for in BeerSmith.
 
Going back to the sugar point balance that Brewfun pointed out:

"Secondly, there is a difference between what your two gravity to volume ratios produce, when they should be identical. The  pre boil number of 1.029 in 60l produces 1740 gravity points (29 * 60 = 1740) Your post boil number is 46 * 47 = 2162. If the two were matched, you either had a pre boil gravity at 1.036 (your prediction) or a post boil gravity of 1.037 (not your measurement)"

This is apparent in your session data that you provided.  This means that either one or more of your volume or gravity readings is not correct.  Your 1 liter loss for trub actually exacerbates the gravity point difference between pre-boil and post-boil values:  46 * 48 = 2208 gravity points.


 
Thanks for taking a look. I must confess, I'm a bit lost now.

Could you answer one question for me please?

Given that the gravity measurements are the two things that are definitely accurate (I have a very good 1.000 to 1.060 hydrometer), what would explain 1.029 boiling down to 1.046 over a one-hour boil?

I also know with precision the water input volume (69l), the grain weight (9kg), and the volume in the fermenters (47l), and as far as I can see I have accounted for all the other parameters with a reasonable degree of accuracy. I would understand why the estimated pre-boil gravity was be so much higher than the measured pre-boil gravity because that could have been down to a much lower efficiency, the crucial thing is why that lower (say 62% efficiency) pre-boil gravity then turns into the originally predicted (say 77% efficiency) final gravity in the fermenter. Is even possible that a terrible mash efficiency could be transformed by the boil?
 
mightyhor said:
Thanks. How do I download in that format? It only seems to download in a .docx format from the website.

The answer to the first two statements is 'false'. The final three statements are a little confusing, and I'm not clear why these variables would affect the gravity to volume ratios so drastically.

The measurements were taken from the fermenter at 20?C, and there was trub in the kettle that was accounted for in BeerSmith.

Thanks for the file. I think Oginme and I are zeroing in on the same points to consider.

The first thing I notice is that your measured fermenter volume is 7l less than your target. Where did that volume go?

The next thing I notice is that your pre boil volume matches your target. The pre boil gravity field is white, so that means you made an input. The Measured OG field is still yellow, indicating you didn't update it. This makes the Measured OG a probable variable. 

So, it seems you had low extraction from the mash. Even correcting for temperature, or a calibration issue, you top out at 1.032 for pre boil assuming volumes are correct AND you actually had 1.046 for a measured OG.

Here's what I did:
1) I changed the batch volume to 40l.
This had the result of changing the pre boil volume to about 53l

2) I increased your trub loss to 3l, which better models the amount of wort retained by your hops and malt protein, plus a liter of unrecoverable wort.

3) I increased the boil time to 90 minutes, to account for some of the missing volume.
Of course, you could have had more boil off in 60 minutes, but I stayed with your equipment number in this case. However, it's important to note that cooler winter/spring days can increase boiloff over summer days. There's simply more evaporation potential.

4) I changed the BHE to 65%, which is what BeerSmith is calculating.
This had the effect of bringing your mash efficiency down to about 70%, which is close to what you expected in your original post. Again, this points to an extraction issue in the mash. That could be pH, milling, sparge method or just plain luck of the draw. You didn't record the pH or the final runnings, so no way to be more sure.

Attached are my revisions.
 

Attachments

  • Pale-Ale-8-revised.bsmx
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mightyhor said:
Given that the gravity measurements are the two things that are definitely accurate (I have a very good 1.000 to 1.060 hydrometer), what would explain 1.029 boiling down to 1.046 over a one-hour boil?

I also know with precision the water input volume (69l), the grain weight (9kg), and the volume in the fermenters (47l)...

These all cannot be true to get the outcome you reported. For instance, the fermenter volume is NOT 47l, you recorded 40l.  It's also a but unusual for any single batch to completely fall into whole unit increments.

You don't have any reason to be defensive, though. You did make a respectable beer, after all. And we're operating under the premise that you're seeking information, not validation. So, forgive me if I want to question other numbers, but you *might* have to accept that you just fucked up a little. It's ok, we all do. None of us are able to be all that perfectly accurate.

and as far as I can see I have accounted for all the other parameters with a reasonable degree of accuracy.

Yes, we respect that and started with that premise. Again, don't dig your heels in if we're finding variables for you.

I would understand why the estimated pre-boil gravity was be so much higher than the measured pre-boil gravity because that could have been down to a much lower efficiency, the crucial thing is why that lower (say 62% efficiency) pre-boil gravity then turns into the originally predicted (say 77% efficiency) final gravity in the fermenter. Is even possible that a terrible mash efficiency could be transformed by the boil?

I believe you've underestimated your trub loss and boiloff. You overstated your yield, which is going to artificially increase your efficiency because you're stating a larger percentage of sugar made it into the fermenter.
 
brewfun said:
but you *might* have to accept that you just f**ked up a little. It's ok, we all do. None of us are able to be all that perfectly accurate.

First, THIS... I've been brewing for a long time and have moderate experience in BS (only been using for about the last year, maybe 20 batches) and still make mistakes...

second, to hopefully add some here, is the recipe and session data you recorded accurate? how long did you boil? how much do you ACTUALLY lose to trub? I've missed my pre-boil several times. this can be attributed to a number of things, usually for me its hurrying my sparge.

What i see on your recipe is you got bad efficiency in the mash, this sucks, but sometimes happens. the real questionable deviations here become the difference in pre-boil and "batch" numbers.  the amount you would've had to boil off to get from 60L of 1.029 to 1.046 would be like 25L and your volume into the fermenter doesn't reflect that much loss. So this is literally impossible.

This would correspond with brewfun questioning the accuracy of the numbers you have.

to put it quite simply, somewhere you got an inaccurate reading. why or where? i can't say as i wasn't there. hydrometers lose accuracy, temperatures may not be perfect, there's all sorts of potential discrepancies in the process! Heck, one of my recent batches i lautered about 15 minutes longer than usual and got 5pts higher than i usually do. hitting 91% mash efficiency really messed with me! one recent brew i only had 65% efficiency! knowing your setup and brewing consistently makes it all go a lot smoother.
 
brewfun said:

Thanks both for taking the time to look at this, and apologies if I came across as defensive ? in my head this is a very simple problem that must have a simple solution, i.e. I just cannot reconcile 1.029 boiling down to 1.046, or figure out whether that's actually possible.

I have no doubt that I've messed up somewhere ? principally in how I use BeerSmith. Normally I brew based on long experience of things just working, basically just using BeerSmtih to generate IBU and OG estimates, and checking that I've hit the latter.

What I'm thinking now is that my IBUs have probably been off in the past because of these other variables.

Re. the fermenter volume, that was just a clerical error ? it is 47l.
 
dtapke said:
So this is literally impossible.

Thank you! This is what I thought, and why it's so frustrating!

I've just thought of a possible explanation ? I wonder whether the pre-boil reading I took wasn't from wort that was mixed together properly, but had a higher percentage of sparge water.  I did scoop it off the top of the kettle.

*hand slaps face*
 
You asked for help and right now you have two of the best minds on this forum, and me, trying to help.  As dtapke stated, we all screw up every once in a while.  The fact that you, and the rest of us, cannot rationalize the gravity change is a pretty good indicator that something is off with the readings and now the mission is to figures out where the most likely source of the error is so that you are not constantly fighting the software or your expectations.

In terms of your IBU being off, that is another topic entirely which has been discussed on other threads if you search the forum.
 
Your help is much appreciated, and I think that it must be the pre-boil gravity reading that was off (or more specifically the way I took the sample was flawed). The issue is so stark it has to be something like that I think, and not the software/small innaccuracies in variables.

I will definitely be going over my equipment profiles based on your advice though.

I must also stop using en-dashes as they appear as question marks.
 
If i only kept a log of every mistake i've made.... That's a scary concept!

If i were to guess, you probably hit your pre-boil gravity just fine, and got the expected mash efficiency. One of the biggest things i've learned in 15ish years of brewing, IT WILL BE BEER! More than likely it'll even be pretty good beer assuming nothing goes horribly wrong during fermentation!

Make another batch with the same ingredients and see how it goes. If i'm to correctly assume your malt costs are drastically incorrect, you've only got about $30 in ingredients there. (unless you're really paying $24 usd/lb for caramalt... if so, find somewhere else to buy it!)

a good slow sparge will produce a delineation between the cooler dense wort you first collected, and the hot less dense sparge water. If you scooped water off the top before it boiled, or didn't thoroughly stir the wort pre-boil, your reading is gonna be off.
 
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