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Pre-boil gravity calculations

 
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fseider




Joined: 10 May 2013
Posts: 156
Location: Two Naked Frogs Brewery; Reading, PA (USA); Interests: Beer, Frogs, Steampunk, Being Naked


PostLink    Posted: Wed Feb 15, 2017 5:55 pm    Post subject: Reply with quote


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I have a question around Gravity that I'm struggling with. This applies to all recipes really.

Can I presume the "Original Gravity: 1.058 (1.050 - 1.070)" is POST boil (vs pre-boil) ?

If so, the pre-boil volume in the Boil Kettle is set to be at 14.9. This will undoubtedly give me a different gravity reading than post-boil. But knowing what I should anticipate at pre-boil allows me to do any adjustments, such as add some LME or DME to get my numbers back up.

If the above presumption is correct, I have to believe that there are formulas on how to calculate my pre-boil gravity. Any help on this will be appreciated.

(I really have not dug deep enough into BeerSmith yet, so my apologies if it's there in front of my face.)

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Two Naked Frogs Brewery, Winery, & Meadery
Reading, PA
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kal
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Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Wed Feb 15, 2017 6:02 pm    Post subject: Reply with quote

fseider wrote:
I have a question around Gravity that I'm struggling with. This applies to all recipes really.

Can I presume the "Original Gravity: 1.058 (1.050 - 1.070)" is POST boil (vs pre-boil) ?

Correct. Whenever someone talks about original gravity (OG), they always mean immediately before fermentation. Final gravity (FG) is always after fermentation.

Quote:
If so, the pre-boil volume in the Boil Kettle is set to be at 14.9. This will undoubtedly give me a different gravity reading than post-boil. But knowing what I should anticipate at pre-boil allows me to do any adjustments, such as add some LME or DME to get my numbers back up.

We boil for 90 minutes so more is collected pre-boil to account for the longer boil time as more water is boiled off.
Collect as much as you require in the boil kettle to end up at 1.058 after the boil. All systems boil off at different rates.

Quote:
If the above presumption is correct, I have to believe that there are formulas on how to calculate my pre-boil gravity. Any help on this will be appreciated.

All brewing software I've seen has the necessary calculators built in. You can also google "pre-boil gravity calculator" for many online versions and choose which you like best.

Good luck!

Kal

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fseider




Joined: 10 May 2013
Posts: 156
Location: Two Naked Frogs Brewery; Reading, PA (USA); Interests: Beer, Frogs, Steampunk, Being Naked


PostLink    Posted: Wed Feb 15, 2017 7:41 pm    Post subject: Reply with quote

Oh wow, that was too easy. Google search came up with a lot of easy info. Not sure why I had thought this was going to be tricky originally.

For those interested - Pre-Boil Gravity for this recipe is 1.047 using the above recipe parameters.

Thanks.

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Fred Seider
Two Naked Frogs Brewery, Winery, & Meadery
Reading, PA
"What's in your goblet?!"
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Model 30A; SN 0130
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kal
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Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Wed Feb 15, 2017 7:55 pm    Post subject: Reply with quote

fseider wrote:
For those interested - Pre-Boil Gravity for this recipe is 1.047 using the above recipe parameters.

Yup. That's what my software (Beer Tools Pro) tells me too.

If that's the only number you want and your software doesn't have it, it's deceptively simple to calculate:

Going from 14.9 to 12 gallons is a 14.9/12 = 1.24 change
So final gravity of 1.058 has to have the same change (58/1.24 = 47, or 1.047)

Kal

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Our new shop with over 150 new products: shop.TheElectricBrewery.com
We ship worldwide and support our products and customers for life.
Purchasing through our affiliate links helps support our site at no extra cost to you. We thank you!
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fseider




Joined: 10 May 2013
Posts: 156
Location: Two Naked Frogs Brewery; Reading, PA (USA); Interests: Beer, Frogs, Steampunk, Being Naked


PostLink    Posted: Wed Feb 15, 2017 11:13 pm    Post subject: Reply with quote

For a SUPER SIMPLE spreadsheet version that maintains the actual gravity reading vs points, see the attached file. Useful if interested in the formula.

And apologies - this whole thread should have been posted under 'Using Your Brewery'. Kal - Is it possible for you to move?



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Calc.jpg



Pre Boil Gravity Calc.xlsx
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_________________
Fred Seider
Two Naked Frogs Brewery, Winery, & Meadery
Reading, PA
"What's in your goblet?!"
---
Model 30A; SN 0130
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kal
Forum Administrator



Joined: 12 Dec 2010
Posts: 11116
Location: Ottawa, Canada

Drinking: Pub Ale, Electric Creamsicle, Mild, Pliny the Younger, Belgian Dark Strong, Weizen, Russian Imperial Stout, Black Butte Porter


PostLink    Posted: Thu Feb 16, 2017 12:20 am    Post subject: Reply with quote

Good idea. Thread split!

Kal

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Ozarks Mountain Brew




Joined: 22 May 2013
Posts: 737
Location: The Ozark Mountains of Missouri


PostLink    Posted: Thu Feb 16, 2017 2:02 am    Post subject: Reply with quote

don't forget when reading your preboil gravity you need to recirculate or stir a bit first before testing because the last bit of sparg is almost strait water and the thicker wort is on the bottom
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