Author Topic: How does this Extract calculation work  (Read 941 times)

Offline jeeyeop

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How does this Extract calculation work
« on: November 19, 2015, 09:36:10 PM »
Hey guys, so I'm reading through Jon Palmer's How to Brew, and there was a section that confused me a bit.

On page 107 he lists the recipe of a Typical American Lager Beer
-3.5 lbs pale DME, gravity point = 49
-1.5 lbs dry rice solids (powder), gravity point = 21
-3 Gal BG = 1.049
-5 Gal OG = 1.042

Can anyone tell me how you get both of those gravities? This isn't really a necessity for me to know, but it's bothering me that I don't! Thanks!
« Last Edit: November 19, 2015, 09:38:04 PM by jeeyeop »

Offline muzak

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Re: How does this Extract calculation work
« Reply #1 on: November 19, 2015, 09:41:36 PM »

-3 Gal BG = 1.049
-5 Gal OG = 1.042


It's not shown, but I'm assuming this is a partial boil recipe based on the two numbers given.

The first number, 1.049, is the gravity of the wort in the boil kettle. The second number, 1.042, is the gravity after the top up water has been added to the fermenter.

The addition of water will dilute the wort and cause the drop in gravity.
John L.
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Planning: Simcoe SMaSH
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Drinking: Saison, Amber Ale, APA, American Strong Ale

Offline jeeyeop

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Re: How does this Extract calculation work
« Reply #2 on: November 19, 2015, 09:52:45 PM »
Yep, it's a partial boil. I was more concerned over how he got the 1.049 and 1.042 gravity themselves and if it can be deduced from the numbers shown (or at least estimated if efficiency is also a factor)?

Offline a10t2

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Re: How does this Extract calculation work
« Reply #3 on: November 19, 2015, 10:38:45 PM »
It is just an estimate using this method (though certainly close enough for brewing), but efficiency is not a factor for extract brewing:

OG = m*PE/V

where m is the mass (lb), PE is potential extract (either "point-gal/lb" or %, if % multiply by 46.2), and V is volume.

DME and rice solids both have PE of ~42 point-gal/lb, so:

(3.5 + 1.5)*42/5 = 42

or 1.042 OG in 5 gal. The 3 gal gravity is confusing using the information here, but I'm assuming the directions call for the rice solids to be added late in the boil:

3.5*42/3 = 49
« Last Edit: November 19, 2015, 10:40:25 PM by a10t2 »
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Offline jeeyeop

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Re: How does this Extract calculation work
« Reply #4 on: November 19, 2015, 11:44:18 PM »
thanks for the help!