Losing efficiency during the boil - could use some help

[cactusgarrett]

This is my fourth batch on my new Brewzilla 65L, and I'm having problems troubleshooting an issue; thought you all could help:

The first batch was relatively lower OG (a helles) and I hit targets fine - except for too much pre-boil. After some tweaks to my spreadsheet and predictions, over the next few batches I dialed in everything to hit predicted pre and post-boil volumes, as well as pre-boil SG. However, today was the third batch in a row where the post-boil gravity is nearly 10 points low compared to the Beersmith prediction.

If I'm hitting the predicted pre-boil and post-boil volumes (by my own spreadsheet), and pre-boil gravity (by Beersmith), what are some possible avenues that I'd be losing gravity?

 

[Bassman2003]

I would guess lower boil intensity or humidity is effecting the boil off rate. If you have the gravity points pre-boil, then the only thing left to change is the amount of water that boils away. I do not understand how your post boil volume is as expected. With a pre-boil gravity reading, your post-boil gravity should be determined with a set end volume.

If you used a lot of hops for example, your post boil volume would be lower which might result in high O.G. Less gravity at the end would mean more water left through the boil.

 

[DBhomebrew]

I'd suspect measuring or math errors. When I'm done with a brew, I like to make a 'as-built' recipe file. If I can't get the software to reflect reality I know something's wrong with my math or measurements.

First off, how do you measure your volume? What's the resolution of your method? Mine is to the ~1.5oz.

Second, are you accounting for thermal expansion? When you figure your gravity points, are you adjusting to room temp for all volumes?

 

[cactusgarrett]

If you used a lot of hops for example, your post boil volume would be lower which might result in high O.G.

That's the thing - this time I used a lot of hops, but my spreadsheet modeling estimated everything just fine. I thought, at first, I wasn't mixing the pre-boil well enough and that that pre-boil gravity, despite looking on-target, was actually lower than measured and targeted. However, the past two times I've stirred the hell out of it, and sampled as the wort came to a boil. With the post-boil volume being nuts on, I'm stumped.

 

[cactusgarrett]

First off, how do you measure your volume? What's the resolution of your method?

I've got a sight glass that's measured out in 1qt increments. All measurements are done hot, except the volume into the fermenter.

Second, are you accounting for thermal expansion?

I am.

I haven't used Beersmith for 100% of the brew day because it previously didn't handle my actual volumes well. After getting this 65L Brewzilla, I've been trying to adjust Beersmith to make a reliable profile, using actuals from each brew day, but it's not going smoothly so I've kept using my spreadsheet for volumes. Only thing i can think of is that I try to force Beersmith to work (again) or do a post-mortem and see if something like Brewfather works better.

 

[DBhomebrew]

What are your measured pre/post volumes and gravities?

 

[cactusgarrett]

What are your measured pre/post volumes and gravities?

Pre: 8.35 gal, hot (target 8.45 gal), 1.046 (target 1.045)
Post: 6.75 gal, hot (target 6.75 gal), 1.054 (target 1.063)

This was a little more boil-off (1.6 gal/hr) than I've typically seen the previous few batches (1.2 gal/hr), further leaving me perplexed as to the lower-than-expected post-boil gravity.

 

[Sammy86]

Pre: 8.35 gal, hot (target 8.45 gal), 1.046 (target 1.045)
Post: 6.75 gal, hot (target 6.75 gal), 1.054 (target 1.063)

That doesn't seem right to me...something is off in BS...that is a very vigorous boil to concentrate that much sugar in a Brewzilla. I have consistently gone up 9 points after the 60 min boil on all my brews. Are you boiling more than 60?

 

[cactusgarrett]

Are you boiling more than 60?

Previous batch was a RIS with a 2 hr boil, and post-boil volume was predicted fairly well. For the first 3 batches I was seeing 1.2 gal/hr but this one I think with the weather being the coldest and me having the 1000 & 2000W elements going, I'm not surprised at the 1.6 gal/hr, for one hour, today.

 

[DBhomebrew]

Pre: 8.35 gal, hot (target 8.45 gal), 1.046 (target 1.045)
Post: 6.75 gal, hot (target 6.75 gal), 1.054 (target 1.063)

Your numbers don't work out. Preboil vol*grav should equal postboil vol*grav.

Measured
8.35*46=384
6.75*54=364

Target
8.45*45=380
6.75*63=425

The discrepancy in measured is close enough to throw it up to minor measurement errors. I'm very surprised by the software's discrepancy. That should be spot on.

Also, does your software account for thermal expansion? Mine does not, all calcs are done at room temp.

 

[doug293cz]

Describe everything you from the time you start to lift the malt pipe, until you take your pre-boil SG reading in gory detail. There are some stratification effects that can be caused by the malt pipe, and if the wort is not adequately homogenized prior to taking the SG sample, you may get an erroneous reading.

You can't lose efficiency (extract actually) during the boil unless you lose wort to a spill, boil-over, etc. If you use a lot of hops, you may need to correct the post-boil volume for the volume occupied by the hops.

Brew on

 

[cactusgarrett]

if the wort is not adequately homogenized prior to taking the SG sample, you may get an erroneous reading.

Pull the pipe, let drain and high heat. I mixed multiple times between pulling the pipe and boil initiation - over the course of 10min - and took 3 readings (about 5min apart; all consistent. I'm confident in that pre-boil gravity reading.

If you use a lot of hops, you may need to correct the post-boil volume for the volume occupied by the hops.

Between the mash hop and boil hops, I used over 8 oz of pellets. My spreadsheet accounts for both pellet and whole cone hop absorption, so I've got that covered, and am confident in that since the pre-boil volume target was hit.

 

[cactusgarrett]

One thing I had to do was force Beersmith into a higher pre-boil volume (8.5 gal) versus what it would when calculated automatically (7.85 gal), based on the the volumes I've actually seen over the past few sessions. Checking that box and accepting the 7.85 gal pre-boil increases the gravity, but still doesn't resolve the post-boil gravity discrepancy.

Getting the "Calc automatically" value to match with my empirical value still eludes me, despite tweaking a bunch of factors.

Yet, replicating the recipe in Brewfather has the pre-boil gravity at 1.053, which makes the post-boil gravity discrepancy more logical.

 

[doug293cz]

Pull the pipe, let drain and high heat. I mixed multiple times between pulling the pipe and boil initiation - over the course of 10min - and took 3 readings (about 5min apart; all consistent. I'm confident in that pre-boil gravity reading.

Between the mash hop and boil hops, I used over 8 oz of pellets. My spreadsheet accounts for both pellet and whole cone hop absorption, so I've got that covered, and am confident in that since the pre-boil volume target was hit.

Your wort homogenization pre-measurement does not appear to be an issue.

Hop absorption is different than the volume actually occupied by the hops, which will be added to the wort volume, making total volume slightly higher. Hop absorption will be higher than the volume occupied by the hops alone. I haven't done any measurements to determine what the volume/oz of hops is. However, given that hop particles have about the same density as wort, 8 oz of hops should occupy about 8 fl oz of volume.

Have you calibrated the markings on your sight glass? The best way to do this is by adding known amounts of water, 1 - 2 qts at a time. The most accurate way to measure out your calibration volumes is to weigh them on a high precision digital scale (0.01 lb resolution is adequate.) One gallon of water at 68°F (20°C) has a weight of 8.33 lb, so one quart weighs 2.08 lb.

Brew on

 

[cactusgarrett]

Have you calibrated the markings on your sight glass?

Yes, in 1 qt increments, hot.