Author Topic: Low estimated pre boil gravity  (Read 312 times)

Offline wepeeler

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Low estimated pre boil gravity
« on: July 09, 2018, 02:11:53 PM »
So I've done 4 5 gallon batches of BIAB, and I think I have it down pretty well. Getting efficiency between 72-75% on beers up to 1.065. I recently made a RIS, and my efficiency suffered, as it does with a larger grain bill and BIAB. My question with the attached recipe is why was my estimated og so low? When I look over my other recipes, it's usually no more than 10 points lower/different. It was estimated at 1.058, and I got 1.071.

Offline brewfun

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Re: Low estimated pre boil gravity
« Reply #1 on: July 10, 2018, 06:59:49 AM »
This is hard to diagnose because it seems like the session data is incomplete. You have a preboil gravity recorded as 1.071, but post mash is only 1.058? BeerSmith expects the difference to be from kettle sugars and your recipe has none. The mash efficiency is calculated from the post mash number you fill in. If that's brought up to 1.071, your mash efficiency is 71%.

The volumes you recorded don't match what your equipment profile expects. You recorded 5 gallons both pre and post boil, but your profile expects 1.5 gallons of boiloff to concentrate the wort. If you had 1.080 at 5 gallons post boil, then you should have had 6.35 gallons preboil at 1.071. Adjusting preboil volume for this gives mash efficiency at 64.7%, much better than the 58% BeerSmith estimated.

The equipment profile has no losses for trub. Although the batch size is 5 gallons, the estimated post boil volume is 5.5 gallons there. Just adding 0.5 gallons of trub loss, plus making the post mash gravity and preboil volume correct, raise the estimated brewhouse efficiency to just under 64%, much closer to what you seem to have achieved.

The bottom line is to just make sure your measurements are accurate and incorporated into the equipment profile. It can take many brew sessions to dial it all in.
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Offline Kevin58

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Re: Low estimated pre boil gravity
« Reply #2 on: July 10, 2018, 10:29:13 AM »
It sounds from the discrepancies in volume measurements that you haven't properly done your equipment profile set up. You need to make those measurements of boil off rate... grain absorption loss... trub loss etc in order for the software to work properly for you. I use a pump and plate chiller so I even went to the trouble to carefully measure how much liquid I leave behind in this equipment and even the hoses that connect them. And it wasn't insignificant either!

Watch these videos. The first one from Brulosophy. The second gets into how to measure ALL of your losses throughout the entire system. The Brulosophy channel also has mash profile setup instructions too including one for BIAB. Not a bad idea to do these as well.

https://www.youtube.com/watch?v=QmW7pwQP5mQ

https://www.youtube.com/watch?v=HwEbjOt8OR8
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Offline wepeeler

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Re: Low estimated pre boil gravity
« Reply #3 on: July 11, 2018, 04:10:39 PM »
This is hard to diagnose because it seems like the session data is incomplete. You have a preboil gravity recorded as 1.071, but post mash is only 1.058? BeerSmith expects the difference to be from kettle sugars and your recipe has none. The mash efficiency is calculated from the post mash number you fill in. If that's brought up to 1.071, your mash efficiency is 71%.

The volumes you recorded don't match what your equipment profile expects. You recorded 5 gallons both pre and post boil, but your profile expects 1.5 gallons of boiloff to concentrate the wort. If you had 1.080 at 5 gallons post boil, then you should have had 6.35 gallons preboil at 1.071. Adjusting preboil volume for this gives mash efficiency at 64.7%, much better than the 58% BeerSmith estimated.

The equipment profile has no losses for trub. Although the batch size is 5 gallons, the estimated post boil volume is 5.5 gallons there. Just adding 0.5 gallons of trub loss, plus making the post mash gravity and preboil volume correct, raise the estimated brewhouse efficiency to just under 64%, much closer to what you seem to have achieved.

The bottom line is to just make sure your measurements are accurate and incorporated into the equipment profile. It can take many brew sessions to dial it all in.

I'm not sure what you're seeing in my equipment profile, but everything seems ok on my end. I've been working on tweaking my equipment profile to make it as accurate as possible. But there has to be something I'm missing.

All the volumes that I can manually record are recorded. I cannot change post mash gravity (Beersmith won't let me, and it estimates it automatically), which should equal est pre boil gravity if no more sugar is added. I didn't add any extra, so I don't know why my est pre boil gravity was so much higher than estimated. This was my 4th BIAB, and I've hit all my number so far. I just used a much bigger grain bill this time, and I know my efficiency suffered.

I put 5 gallons into the fermentor. I had roughly another 1/4-1/2 gallon or so that I just didn't add. My preboil volume was 7 gallons and my post boil was 5.5, which is what my equipment profile says. Beersmith also does not estimate BH efficiency. I've had to manually adjust the BH efficiency to get better estimates (after the boil and reading the OG), which has worked until this beer. I know it's because of the larger grain bill, I just want to know why BS estimates my pre boil at 1.058. Seems way low. I got it up to 1.062 after adding the .5 gallon trub loss, but that's still low for an estimated OG of 1.081. I've attached recipe again, accounting for the .5 gallon trub loss.

And thanks Kevin, I've seen those vids on Brulosophy. I used them to help set up my BIAB profile. That's why I'm so stumped.
« Last Edit: July 11, 2018, 04:27:10 PM by wepeeler »

Offline Oginme

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Re: Low estimated pre boil gravity
« Reply #4 on: July 11, 2018, 05:06:43 PM »
OK, let me tell you what I see here in your recipe.

1.  You did not fill in the measured post mash gravity nor the measured pre-boil volume.  The boxes are still yellow, which means that no user measured value was entered.

2.  Your pre-boil gravity was 1.071 as you entered it.  Without a volume figure to match up with this value, there is no way to determine exactly what your mash/lauter efficiency was.  You may have had phenomenal efficiency or you may have added and recovered less wort than the program called for.  Both would have resulted in the higher than predicted pre-boil gravity reading, but there is no way to telling which was the driver.

3.  Your measured OG was 1.080.  If you started with a pre-boil gravity of 1.071 and put exactly 5 gal of wort into the fermenter with a half of a gallon of loss to trub, Then your pre-boil volume should have been 6.2 gallons of wort collected.  Your boil off would have been 6.2-5.5 = 0.7 gallons of water.  Your boil off is set for more than twice that at 1.5 gal/hr. 

4.  Basically, if you look at what Brewfun and Kevin58 have previously stated, this gives the impression that your equipment profile does not reflect your process.

5. In short, GIGO. 
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Offline wepeeler

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Re: Low estimated pre boil gravity
« Reply #5 on: July 11, 2018, 05:41:07 PM »
OK, let me tell you what I see here in your recipe.

1.  You did not fill in the measured post mash gravity nor the measured pre-boil volume.  The boxes are still yellow, which means that no user measured value was entered.

2.  Your pre-boil gravity was 1.071 as you entered it.  Without a volume figure to match up with this value, there is no way to determine exactly what your mash/lauter efficiency was.  You may have had phenomenal efficiency or you may have added and recovered less wort than the program called for.  Both would have resulted in the higher than predicted pre-boil gravity reading, but there is no way to telling which was the driver.

3.  Your measured OG was 1.080.  If you started with a pre-boil gravity of 1.071 and put exactly 5 gal of wort into the fermenter with a half of a gallon of loss to trub, Then your pre-boil volume should have been 6.2 gallons of wort collected.  Your boil off would have been 6.2-5.5 = 0.7 gallons of water.  Your boil off is set for more than twice that at 1.5 gal/hr. 

4.  Basically, if you look at what Brewfun and Kevin58 have previously stated, this gives the impression that your equipment profile does not reflect your process.

5. In short, GIGO.

1) I cannot change the post mash gravity. It's been grayed out in BS. It's been set at 1.062. Pre boil volume was 7 gallons, which I have entered in. I'm guessing my exported file doesn't match, for some reason.

2) 7 gallons is the pre boil volume.

3) 7 gallons of pre boil. 1.5 boil off rate. 5.5 gallons post boil. .5 trub. 5 gallons into fermenter

4) My only guess is the exported file doesn't match up. Everything on my end matches what I have stated.

5) I agree

6) Thanks a lot to everyone trying to help. I had some issues with equipment profile with extract, which of course I sorted just in time to switch to all grain. This is why it's frustrating, because I had finally nailed it for extract.

Offline wepeeler

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Re: Low estimated pre boil gravity
« Reply #6 on: July 11, 2018, 05:46:00 PM »
Also, am I right in thinking that if you get fairly close to est pre boil gravity, you simply change the BH efficiency setting to match your post boil gravity? That gives overall efficiency? Used for dialing in different types of beer ie lower gravity ipas vs imperial stouts, where efficiency is going to be different.

Offline Oginme

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Re: Low estimated pre boil gravity
« Reply #7 on: July 11, 2018, 06:23:44 PM »
OK, your overall or brew house efficiency is the amount of sugar from the mash and sugar additions which make it into the fermenter.  In BeerSmith, this number controls the mash efficiency calculations and OG calculation.  From this and the process losses, the program calculates the pre-boil gravity and volumes pre-boil and from the mash.  Further the mash losses and grain absorption values helps to calculate the initial water volumes.

You can update the brew house efficiency in your equipment profile to obtain your actual OG reading.  BeerSmith will calculate the value for you when you fill in all the measured values and that actual brew house efficiency can be found on the 'sessions' tab in the middle row of data right next to the fermented volumes and gravity.  Once you get this number in place, your pre-boil gravity will give you an indicator of how far off your volume balance is.

I find that in my system (also BIAB), that the mash efficiency is pretty flat from pre boil gravities of 1.036 to 1.068 and then starts to decrease for gravities above above 1.069. 
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Offline wepeeler

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Re: Low estimated pre boil gravity
« Reply #8 on: July 12, 2018, 09:23:56 AM »
I'm brewing again tonight. I'll check again to see if all my volumes match. I'll record everything and see where I'm at at the end.

Thanks again.

Offline wepeeler

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Re: Low estimated pre boil gravity
« Reply #9 on: July 12, 2018, 10:57:59 PM »
Just brewed tonight, re-adjusted my equipment profile, and all is well in the world. Nailed all my numbers for my Oktoberfest and went back and re-adjusted for my stout. Thanks everyone for your help.