Author Topic: Missed my estimated OG ... by 14 points!  (Read 4154 times)

Offline Mofo

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Missed my estimated OG ... by 14 points!
« on: June 02, 2015, 10:21:02 AM »
I just googled “missed my original gravity” and got 1,830,000 hits. Here’s number 1,830,001.

I recently did my tenth brew. It was my 6th all-grain brew. I’ve managed to hit or come within a point or two of estimated OG on each. But this last brew, I was not only off, I was off by 14 points!

The recipe was Henrik’s Imperial Amber, from the BS cloud. It has an estimated OG of 1.088 and is the biggest beer I’ve attempted. I rejiggered the recipe so that my brew kit would produce the same estimated OG, IBUs, EBC and ABV. This mostly meant adding a lot more base malt than the original recipe called for, to account for my efficiency. I mash with a 38 liter (10 gal) Gott-style cooler and boil in a 33 liter (9 gal) kettle.

The rejiggering was done with BS2, but I plugged all my brew day numbers into a spreadsheet I’ve been building since I started all-grain (i.e. not long ago). I attach that spreadsheet reluctantly because it feels like going out in public in my underwear.

Measuring for volume, SG and now pH has been beneficial, but I need the help of the brew gurus here to analyze data and hopefully see where things went south. I understand that it’s likely not a single thing that went wrong, but a combination of things. Analyzing numbers has taught me a few things (I think!) and left me with more than a few questions. For anyone willing to wade into my spreadsheet, my immense appreciation awaits. Warning: I’m an American metrics convert.

Spreadsheet Key:
• Basic brew info is across the top
• Right-hand side is most of the info you’d find in the BS Equipment Profile. Figures in black are averages, green and blue are for this brew.
• Color-coded sections follow the process: Water, Mash, Boil, and Ferment (Bottling and Tasting Notes to be added)
• Colored arrows “⌦” at the center of each section toggle between a chart view and the actual worksheet where I plugged in numbers.

As for what I learned and what I still don’t get…

The big discovery I made (again, I think!) is that I lost 5 points in my mash and another 9 points in the boil. Or maybe I’m conflating the data: The estimated pre-boil gravity was 1.069. Mine was 1.064. Then for the boil I was supposed to go from 69 to 88 (19 points), but instead went from 64 to 74 (10 points). A difference of 9 points. Am I misunderstanding this?

As for what went wrong in the mash, my best guess is that I didn’t use pH 5.2 stabilizer and needed to with a big beer like this. My strike water pH measured 6.6 but when I drained the tun 45 minutes later it was 5.0. (I know now that I should just “fire and forget” with pH 5.2 and/or take a pH measure sooner in the mash.) Another guess is that I didn’t uncap and stir the mash. I maintained a steady, perfect temp throughout the 45 minute rest, but maybe I had pockets I should have stirred out. I don’t think the problem was my crush, because I used the same mill I’ve used in all previous brews, when I’ve hit my numbers. Or maybe the problem is just that I can’t mash an 80+ beer in a 10-gallon Gott while my mash efficiency is 73%.

As for the boil, I’m clueless. My mid-boil SG was 1.065, only a single point higher than my pre-boil gravity! I had backed off the flame very slightly for this brew but my evaporation rate was nearly the same as it’s been in previous brews. I know now that I should have used the Boil Off tool as soon as I had my new pre-boil gravity. But I did use it at mid-boil and and decided to go 30 minutes past my original 90-minute boil. Still, it gained me only 2 points. The thing is, in order to have gone from 69 to 88 inside a 90-minute boil, my evaporation rate would have to be 16%.

[Edit: I’ve just looked back at the original Henrik’s Imperial Amber recipe and see that their boil volume is nearly 2 liters less than my 30-liter boil volume, though its post-boil volume is nearly the same at 25.15 liters. But according to the Boil Off tool, to finish the boil with 25 liters of wort that had a starting gravity of 1.069, you’d need an evaporation rate of only 5%. And that gets you a finished wort with an OG of only 1.078! So I’m even more confused. How did they ever get to 1.088!?]

Lastly, if you're tired of answering people’s “missed OG” questions, but fancy yourself a spreadsheet king, I’d really appreciate suggestions on how I could improve mine. It’s a work in progress and there’s a lot to add, including some obvious calculators, but it’s far enough along to see the general direction I’m taking it. I didn't know how to make a chart when I started it. Like brewing, there's a lot more to learn here, too. As I said, I feel like I'm only in skivvies; toss a man some trousers!

And if you don’t have input on either front, I still appreciate your having read this far. Thanks for the moral support!

And cheers!
« Last Edit: June 02, 2015, 11:09:59 AM by Mofo »
bottled: Wee Heavy, Belgian Wit
fermenting: Imperial IPA, Citra Pale Ale

Offline Oginme

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Re: Missed my estimated OG ... by 14 points!
« Reply #1 on: June 02, 2015, 11:32:45 AM »
One thing that may help with figuring things out is to do a balance using gravity points.  This is the volume times the specific gravity (generally using just the last two digits, i.e. 1.064 ==> 64).  When you are boiling, you are concentrating the sugars, but none are created or destroyed.  So your gravity points before the boil and after should be the same.

Just looking at the pre-boil vs post boil from your spreadsheet: you have a pre-boil volume of 30 liters at a measured specific gravity of 1.064.  This gives you 30 x 64 = 1920 gravity points.

Post boil you have 24.5 liters at 1.074 specific gravity: 24.5 x 74 = 1813 gravity points.

This indicates an error in either one or more of your gravity measurements or your volume measurements.
Recycle your grains, feed them to a goat!

Offline durrettd

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Re: Missed my estimated OG ... by 14 points!
« Reply #2 on: June 02, 2015, 03:11:25 PM »
Read dmtaylo2's comments in the following thread:    http://forum.northernbrewer.com/viewtopic.php?f=43&t=124471&p=1085516#p1085516

The point is that the higher the targeted OG, the lower your efficiency. That is probably ONE of the effects that led to the lower efficiency.

The bad news is that you'll need to brew some more beer so you can figure out what's going on.   :)

Offline Mofo

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Re: Missed my estimated OG ... by 14 points!
« Reply #3 on: June 03, 2015, 09:17:20 AM »
@Oginme & durrettd, hugely helpful! Many thanks. I'm still not sure what went wrong, but going forward I can use a gravity balance to know if my readings are accurate. I'll write it into my spreadsheet. Thanks!
bottled: Wee Heavy, Belgian Wit
fermenting: Imperial IPA, Citra Pale Ale

Offline Oginme

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Re: Missed my estimated OG ... by 14 points!
« Reply #4 on: June 03, 2015, 09:19:23 AM »
yes, you can and it would flag any issues that pop up.
Recycle your grains, feed them to a goat!