Author Topic: Overall efficiency good but high after mash  (Read 1552 times)

Offline brian_muz

  • BeerSmith Brewer
  • ***
  • Posts: 25
  • Let beer be beer and milkshakes be milkshakes...
Overall efficiency good but high after mash
« on: October 02, 2020, 12:34:44 AM »
Hi all,

I'm sure this is something obvious but I can't get my brain around it at the moment. The last few brews I've done I've ended up spot on or very close to the forecast OG in BeerSmith. However, my actual gravity post mash/start of boil has been about 0.008-0.010 points higher than what BS forecast. I've been watching my volumes and they seem to line up. Can't work out why this would be out. Any ideas?

Offline GigaFemto

  • BeerSmith Grandmaster Brewer
  • *****
  • Posts: 356
  • Muonic Matter Rocks!
Re: Overall efficiency good but high after mash
« Reply #1 on: October 02, 2020, 11:30:31 AM »
When BeerSmith gives a pre-boil gravity it means the gravity at boiling temperature. We don't measure that. We cool the sample down and measure it at room temperature, which gives a higher value because of the thermal expansion of the boiling water. Your equipment profile has a "cooling shrinkage" number that is usually 4%, the shrinkage of water from boiling to room temperature. That accounts for part of your issue, but that wouldn't usually give 8-10 gravity points. I often have trouble getting a good  pre-boil measurement, and I think it is because of stratification. You have to make sure that your wort is mixed up very well before taking your sample.

--GF

Offline Oginme

  • BeerSmith Grandmaster Brewer
  • *****
  • Posts: 3150
  • Goats, guitars, and a home brew; Life is good!
    • Longvu LaManchas
Re: Overall efficiency good but high after mash
« Reply #2 on: October 02, 2020, 12:58:20 PM »
To understand where your issue may be coming from, we will need a bit more information.  I would suggest for the best advice that you export the recipe in question as a .bsmx file and post it here so we can see your process, volumes, and gravity readings as compared to the calculated targets.

With respect to GF, one of the issues with BeerSmith is not that it gives a gravity at boiling temperatures, but that it calculates the gravity based upon the boiling volume and uses the cold gravity and volumes for the amount of sugars.  It never normalizes the hot volume to room temperature before applying the gravity point calculation for the post-mash/pre-boil gravity. 
Recycle your grains, feed them to a goat!

Offline brian_muz

  • BeerSmith Brewer
  • ***
  • Posts: 25
  • Let beer be beer and milkshakes be milkshakes...
Re: Overall efficiency good but high after mash
« Reply #3 on: October 02, 2020, 03:41:04 PM »
Thanks for your replies. I've attached my records from the brew. The "Expected" column is the forecast values from BeerSmith. I'll export the recipe and post it here too.

Offline brian_muz

  • BeerSmith Brewer
  • ***
  • Posts: 25
  • Let beer be beer and milkshakes be milkshakes...
Re: Overall efficiency good but high after mash
« Reply #4 on: October 02, 2020, 03:44:51 PM »
...and here is the .bsmx file from the brew. I've updated it with my actual numbers.

Offline Oginme

  • BeerSmith Grandmaster Brewer
  • *****
  • Posts: 3150
  • Goats, guitars, and a home brew; Life is good!
    • Longvu LaManchas
Re: Overall efficiency good but high after mash
« Reply #5 on: October 04, 2020, 09:18:34 AM »
I've had a chance to go through your numbers.  Here is what I take from the values you measured versus the target.

The first thing I did was to line up all your volumes and then make a correction for the thermal expansion.  IT is assumed that the volume reading at start of the boil is taken at the fully thermal expansion of 4%.  I applied the same to the volume from the mash, though if you were at 60C, your thermal expansion coefficient is around 2.2%. 

I looked at the gravity point balance through the system.  Ideally, since there are no losses or additions of sugar from the start of the volume to the end of the volume and your profile does not show any addition of water after or before the boil, the gravity points at the beginning of the boil and the gravity points at the end of the boil should be the same or within measurement error.

In your figures, you ended the boil with 1508 gravity points when you measured the cool volume, but had 1604 gravity points (volume adjusted for temperature) at the end of the boil.  This accounts for a significant loss of sugars without any change in volume, so it suggests that your measurement might be off.  This would also explain the difference before and after the boil, where you started (adjusted volume figures) the boil with 1754 gravity points but ended up with 1604 gravity points. 

Two things to consider: 

1) gravity measurements should be made on chilled wort to be the most accurate.  When the wort temperature is much higher than ambient, the wort is continually losing heat and so you are trying to take a measurement on a moving target.  You don't say your measurement process, but I bring this up as it is a common issue.

2) If you are taking your volume measurements based upon a pre-etched kettle, I would recommend checking them using a calibrated measuring cup, or better yet with a scale and making a measuring stick as you carefully measure out consistent room temperature water into the kettle.  I have a post in the equipment section on setting up my Anvil Foundry which illustrates my process for making a calibrated measuring stick.  The important aspect of creating a measuring stick with temperature is making sure your water temperature is at or close to 20C.  I used a Gott cooler to hold the water needed and keep that temperature constant through the measurement process.  At this temperature, the weight of 1 liter of water is 998.2 grams.

Since you ended up pretty close to your target gravity in the end with a very low error, this would suggest that your ending measurements match your profile fairly close.  I would recommend getting a handle on your hot side measurements and seeing how that plays out for you.

I know there are no specific answers here, but hope it helps in troubleshooting.  I have attached the spreadsheet where I stepped through the calculations so you can follow.
Recycle your grains, feed them to a goat!

Offline brian_muz

  • BeerSmith Brewer
  • ***
  • Posts: 25
  • Let beer be beer and milkshakes be milkshakes...
Re: Overall efficiency good but high after mash
« Reply #6 on: October 11, 2020, 05:14:22 PM »
First of all, sorry for my delayed reply. I wrote out a full reply several days ago but my PC restarted before I posted it.

Second, thankyou so much for you thoughts and detailed reply. It blows my mind that people on forums are willing to go into my data and help me understand what's going on. I really appreciate it.

In terms of how I take my measurements I ensure I always chill my wort to ~20C before taking a gravity reading. So I'm confident I can rule that out.

My volume measures I'm reasonably confident in but I could get better. I've checked my HLT, mash tun and boil kettle to make sure the volume markings were accurate. I didn't do this by weight but I used a 5L measuring jug that is my source of truth for volumes. I'd say all three vessels were accurate within about 100-200ml. One thing though that does make it difficult is that my mash tun and boil kettle only have makings at 5 litre intervals (why manufacturers don't go do to 1 Litre increments at a minimum is beyond me. It's such an easy way to improve the product). This makes volume recording a bit more of an approximation than it should be. I'll take your advice and make a measuring stick for each one so I can really dial this in.

On discussion with my homebrew club a number of people said they had gone away from taking gravity readings with a refractometer and have moved back to a hydrometer instead. Members didn't seem certain if their strange refractometer readings were a result of inaccuracy in the refractometer itself or if it had more to do with taking small samples from the top of the kettle (if there were some stratification in the sugar levels in the wort). However, many said they had sometime found results they didn't trust using a refractometer. I found this really interesting as I assumed everyone used refractometers and that it was accepted that they were highly accurate. I also assumed that the sugars in wort would be pretty evenly distributed throughout the volume. I'll try using only my hydrometer next brew day. It's just another possible error point that I can easily test.

I also really liked your focus on gravity points. I haven't looked that this before but it makes complete sense. I can easily build this into my brew day records so I can see if there is any variance from the start to the end of the boil.

Thanks again for all your help. Hopefully with these few tweaks I can increase the accuracy of my records and dial in my profile a little more.

Offline Oginme

  • BeerSmith Grandmaster Brewer
  • *****
  • Posts: 3150
  • Goats, guitars, and a home brew; Life is good!
    • Longvu LaManchas
Re: Overall efficiency good but high after mash
« Reply #7 on: October 11, 2020, 06:21:45 PM »
I find that most of the time people do not clean or check their refractometer with distilled/DO water to make sure it is in calibration.  Once it is calibrated, the refractometer will not tend drift but it will collect a film of dried wort, sugars, and other material which will throw off the readings.  I have gone to taking my brew day readings with a refractometer and about every four or five brews I will double check it against a hydrometer reading.  It saves time and energy for me.  Then again, I also have almost 40 years of practice with refractometers and am well versed in the care and cleaning.

Recycle your grains, feed them to a goat!

Offline GigaFemto

  • BeerSmith Grandmaster Brewer
  • *****
  • Posts: 356
  • Muonic Matter Rocks!
Re: Overall efficiency good but high after mash
« Reply #8 on: October 11, 2020, 10:09:23 PM »
I store my refractometer in the garage and I brew in the kitchen. During the winter the garage gets much colder than the kitchen. As the refractometer warms throughout the brew day the zero drifts significantly. I check the zero with distilled water before every measurement.

--GF

Offline Oginme

  • BeerSmith Grandmaster Brewer
  • *****
  • Posts: 3150
  • Goats, guitars, and a home brew; Life is good!
    • Longvu LaManchas
Re: Overall efficiency good but high after mash
« Reply #9 on: October 12, 2020, 03:33:35 AM »
GF brings up a good point.  My refractometer is kept in the kitchen at a constant temperature.  Thermal shrinkage and expansion of the prism and body of the refractometer can cause a significant change in reading.
Recycle your grains, feed them to a goat!

Offline brian_muz

  • BeerSmith Brewer
  • ***
  • Posts: 25
  • Let beer be beer and milkshakes be milkshakes...
Re: Overall efficiency good but high after mash
« Reply #10 on: November 02, 2020, 02:46:19 AM »
Thought I would circle back on this one. Today I did the first beer after the one that started this thread and I made two changes:
1) I used a 1m metal ruler as a dip-stick. To calibrate it for my HLT, mash tun, boil kettle and fermenter I used a 5L jug which I calibrated by weighing out 20 degree water. It took several hours to do them all but I now have a measure which goes down to the mm which I can really trust.
2) I abandoned the refractometer for this brew and only used my hydrometer.
The results were really interesting. When if came to the etched markings in my boil kettle and fermenter they were significantly out. As in >1 litre out when brewing a 19L batch!
I've attached the .bsmx in case anyone is interested but it looks like my efficiency might be ~10% better than what I was working with.
I'll need to do a few brews with the new calibrated measures to confirm these settings but it looks like I'm getting much "closer to the hole" (golf reference, not a euphemism).
For anyone who finds this thread down the track (I'm always reading old threads when researching so I like to close out my own) my learnings are:
-Don't trust the measurements on even pricey, brand name vesels. Pretty much all four of mine were out. Some high, some low, and some more significant that others.
-Do a brew now and then without a refrac. Another options, which I plan to do with my next brew, is to take all readings with both to understand how close they are.
...so pretty much what everyone said. Thanks for the replies!

 

modification