Author Topic: Trouble dialing in my equipment profile  (Read 276 times)

Offline brian_muz

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Trouble dialing in my equipment profile
« on: April 27, 2019, 04:19:23 AM »
I've been trying to dial in my equipment profile over my last couple of brews and I'm scratching my head to work out where I'm out.

My setup

I have an electric digiboil which I use as a HLT
I have a plastic Gatorade cooler which I use with a BIAB bag for mashing - There is zero dead space as a result
I batch sparge and then squeeze the grain bag
I have a standard stainless steel boil kettle which I heat over gas - I lose 2 litres when I train this

On my last brew my numbers were:

Post mash gravity - 1.047 predicted - 1.051 actual (so I was a little ahead at this stage)
Pre boil volume - 28.17 predicted - 29.5 actual (I'm guessing I got a little more water through bag squeezing?)
Batch size is set at 19 but I ended up with 20.5 (So I think my evaporation rate is right but I still had ~1.5 litres additional water from the start
OG - 1.068 predicted - 1.063 actual.

Looking at this now two things don't make a lot of sense to me:

1) Given I have no dead space in my mash tun where did the additional 1.5 litres come from? Is this just bag squeezing?
2) My gravity was a little above prediction pre boil and my evaporation rate seems to have been dead on. Why then have I gone from 4 points up pre boil to 5 points down post?

My recipe did call from 0.45kg of honey with 15 mins to go in the boil but I'd assume the calculations for this in terms of impact on gravity would be pretty accurate.

Any other thoughts?


Offline Oginme

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Re: Trouble dialing in my equipment profile
« Reply #1 on: April 27, 2019, 05:38:11 AM »
You gave a pretty good description of your process which will help.

The easiest thing to tackle is your squeezing of the bag.  This changes the grain absorption figures for the standard brewing and you will need to calculate this out.  Take your initial water charge into your cooler mash tun minus the volume of wort you collected and divide this by the weight of your grain bill.  This will give you the volume of water retained in the grains.  Convert this to fluid ounces of water per ounce of grain because that is the units BeerSmith uses.  You will need to update this in the global options by clicking on 'options' > 'advanced' and entering your calculated number into the 'grain absorption' box. 

Next, you are using a cooler mash tun.  I am assuming that you are upending the cooler to get the last of the wort into the boil kettle otherwise there still may be some wort left in the bottom of the cooler after draining it.  If you are not pouring this volume into the kettle, then you do have some mash tun dead space and will need to measure that volume.

Your boil off is pretty straight forward.  You started with 29.5 l and ended with 20.5 l.  I would guess that the ending volume is after chilling.  At what temperature was your pre-boil volume measured?  Boiling or at mash temperatures?  This makes a difference in the amount of thermal shrinkage between the hot volume and room temperature volumes.  You will need to correct the volumes to the same temperature, so if your pre-boil volume was at or near boiling when you recorded it, it contained around 4% thermal expansion from room temperature.  Take your room temperature volume of 20.5 l and multiply it by 1.04 to get a near boiling volume (20.5 * 1.04 = 21.3 l).  Your boil off was then 29.5 - 21.3 = 8.2 litres.

Now, based upon your volume at the end of the boil, 0.45 kg of commercial honey would give you approximately 7 points of gravity.  Without those 7 points, your actual gravity would have been 1.056 [1.063 - .007].

Using this figure and your volumes, you can check the accuracy of your readings.  If you follow the sugar points for just the wort alone (not including the honey) the figures should be equal (or pretty close) pre-boil to post-boil.  For sugar point, take the gravity points for the reading [ (gravity reading - 1) * 1000] and multiply it by the volume measured at that stage.  So your pre-boil sugar point number becomes 51 * 29.5 = 1504.  The post boil sugar point number is your gravity reading at the hot volume or 56 * 21.3 = 1193.  These numbers are not even close.

If we use the actual reading of 1.063, the number is 63 * 21.3 = 1278, indicating that just leaving out the honey was not the issue.  It does suggest that one or more of your readings was not reliable.

How do you measure your volumes?  If you are relying on preprinted or etched numbers on your kettle, then I would highly recommend that you create a measuring stick by using a tape measure and measuring the depth of liquid with known volumes of water in your kettle.

The other and more probably the issue would be with one of your gravity measurements.  Make sure your wort is well mixed and chill your samples down to temperatures close to the calibration temperature of your hydrometer.  This temperature is usually around 60 F/15.6 C and should be marked on the paper scale inside your hydrometer.

If you are using a refractometer for your readings, I recommend using the Brix scale for your measurements and converting the number to specific gravity.  Refractometers are calibrated for Sucrose and although the refractive index between Sucrose and Maltose is close, there is a difference which creates and error that will increase in size as the gravity increases.  Also make sure your refractometer surfaces are clean and check your zero point with distilled water.  Dried sugars on the prism accounts for a lot of error in readings.  Often overlooked as a source of measurement error when using a refractometer is the possibility of dried sugars on your spoon or dropper you use to take the sample. 

Hope this helps start you on the right direction.  Keep good measurements and recheck your values for a few brews and you will bring your equipment profile into alignment with how your process actually performs.


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Offline brian_muz

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Re: Trouble dialing in my equipment profile
« Reply #2 on: April 27, 2019, 06:35:59 AM »
Thanks Oginme for your detailed response!

1) I'll definitely take you advice to account for bag squeezing. Thanks!

2) I don't upend the mash tun as such but the drain point is sunk from the base of the tun and by tipping it slightly I get 100% of the liquid out. I've also rigged up a grate which I slip in post mash (I lift the bag up and place it under before lowering the bag) which helps the bag drain. I found the bag blocked the drain point without it.

3) 20.5 is what I ended up with in the fermenter. I did lose 2 litres to dead space in the boil kettle. On an unrelated note I've always wondered if I should tip the kettle to get all this too. It contains all the cloudy proteins so I've always left this out but a post on the Brulosophy site has me wondering if I should just transfer it all. It would be different if I had hop trub in there but I use a hop screen so this isn't an issue. Anyway, looking at my notes I had 23.8L at flame out (so 100 degrees C). I didn't measure the volume once chilled but I'll start doing this. I always find it hard as I need to lift out the immersion chiller which disrupts the proteins that have dropped out and is also difficult with my low range hood. I'll pay more attention next time. Calculating backwards though It would have been approx. 22.5 when cooled.

4) I'm pretty confident in my volumes. I actually etched the kettle myself after marking off the volumes using a scale to track the weight. I've also "calibrated" my measuring jugs the same way and then made sure they all lined up. It was amazing how far off some jugs were though. I've chucked some out they were so misleading.

I've got a couple of things to dial in here and a couple more to keep an eye on over the next couple of brews. Your sugar point formula is really useful and I'll definitely keep an eye on this to make sure it's balancing out. Might try an calibrate my refractometer too. Or just use my hydrometer as well for a couple of brews.

Thanks again for you help. I really appreciate it!


Offline Oginme

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Re: Trouble dialing in my equipment profile
« Reply #3 on: April 27, 2019, 07:04:23 AM »
Thanks Oginme for your detailed response!

1) I'll definitely take you advice to account for bag squeezing. Thanks!

2) I don't upend the mash tun as such but the drain point is sunk from the base of the tun and by tipping it slightly I get 100% of the liquid out. I've also rigged up a grate which I slip in post mash (I lift the bag up and place it under before lowering the bag) which helps the bag drain. I found the bag blocked the drain point without it.

3) 20.5 is what I ended up with in the fermenter. I did lose 2 litres to dead space in the boil kettle. On an unrelated note I've always wondered if I should tip the kettle to get all this too. It contains all the cloudy proteins so I've always left this out but a post on the Brulosophy site has me wondering if I should just transfer it all. It would be different if I had hop trub in there but I use a hop screen so this isn't an issue. Anyway, looking at my notes I had 23.8L at flame out (so 100 degrees C). I didn't measure the volume once chilled but I'll start doing this. I always find it hard as I need to lift out the immersion chiller which disrupts the proteins that have dropped out and is also difficult with my low range hood. I'll pay more attention next time. Calculating backwards though It would have been approx. 22.5 when cooled.

So your 23.8 l at end of boil would have calculated out to 23.8 * 56 = 1333 sugar points total.  Much closer to the 1504 preboil value, but still some loss there which needs to be accounted for.

I don't transfer all the trub from my boil kettle, but I do tip and transfer as much as I can.  The lighter proteins help provide some nutrition for the yeast, but I don't want to lose fermenter volume to the mass of all the trub and hop debris from the boil kettle.  Anecdotally, I have found my beer clears better and the fermentation is stronger when I do this versus previously excluding much of this material. 

4) I'm pretty confident in my volumes. I actually etched the kettle myself after marking off the volumes using a scale to track the weight. I've also "calibrated" my measuring jugs the same way and then made sure they all lined up. It was amazing how far off some jugs were though. I've chucked some out they were so misleading.

Great!  Too many people rely on pre-printed volumes and end up with irreconcilable numbers.

I've got a couple of things to dial in here and a couple more to keep an eye on over the next couple of brews. Your sugar point formula is really useful and I'll definitely keep an eye on this to make sure it's balancing out. Might try an calibrate my refractometer too. Or just use my hydrometer as well for a couple of brews.

I use both a refractometer and hydrometer for larger brews and use the hydrometer readings to calibrate my refractometer.  It is set up to be able to do this in BeerSmith under the 'refractometer' tool.
 This way if I do small matches (3 l) for experiments or if I just get too pressed for time (or too lazy), I know I can rely on my refractometer readings.


Thanks again for you help. I really appreciate it!
Recycle your grains, feed them to a goat!

Offline dtapke

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Re: Trouble dialing in my equipment profile
« Reply #4 on: April 29, 2019, 07:30:46 AM »
for your gravity readings, did you only take one reading and then move on?

I always take 2-3 sample readings at every process. this is super easy with a refractometer, as it doesn't really take any time or liquid to do. I also make sure to rinse the lens off with ro/di water and dry it with a clean microfiber towel. When drawing my sample i use Borosilicate Glass pipettes and generally squeeze liquid in and out of them 5-10 times to "rinse" them out at every sampling as well. when done sampling they get rinsed with ro/di water so that no sugary liquid sticks to them.

I've had several instances of off readings that I've been able to attribute to a failure of one of those steps. Also, I just had a refractometer break on me. The plastic portion of the body had cracked and i didn't notice it. I did notice that several readings did not line up with where they "should" be, and upon close inspection found the cracked body. i could wiggle the refractometer and get different readings.
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