Author Topic: Does wort evaporate slower than water?  (Read 828 times)

Offline Pi

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Does wort evaporate slower than water?
« on: December 01, 2013, 12:03:32 PM »
Trying to get an accurate evaporation percentage for the system settings in Pro Mash. I am also making adjustments to my RIMS PID. Since i just wanted to run water through system, would i get different results than the same volume of say 1.060? Does water boil off faster than wort? And does Wort heat up faster/slower than water with the same heat being applied.
Is the difference to minuscule to even worry about? Thanks.
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Offline denny

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Re: Does wort evaporate slower than water?
« Reply #1 on: December 01, 2013, 12:32:27 PM »
As far as I've ever been able to tell, they evaporate at the same rate.  There may be some scientific reason why they shouldn't but in practice I haven't found any difference.
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Offline grod

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Re: Does wort evaporate slower than water?
« Reply #2 on: December 01, 2013, 12:51:47 PM »
You have to assume that the water part of wert will evaporate at the same rate as water once it is heated to over 100C.

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Offline punatic

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Re: Does wort evaporate slower than water?
« Reply #3 on: December 01, 2013, 01:07:20 PM »
Yes wort evaporates slower than water. It also boils at a higher temperature than water.  The dissolved solids in the wort cause a boiling point elevation, the same way antifreeze does in cooling water in your car's radiator.  Those same dissolved solids occupy some of the surface area at the liquid/gas interface at the surface of the wort, blocking the water molecules from escaping as quickly as they would if the wort were water.   

Denny is right though.  The difference is small enough to be practically un-noticable.
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Offline a10t2

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Re: Does wort evaporate slower than water?
« Reply #4 on: December 01, 2013, 01:09:50 PM »
If anything, I'd say wort probably boils a little faster than water since it's boiling a few degrees warmer. I would guess that it's a very minor difference though.

Per unit mass, wort will heat up a little faster than water. Its specific heat capacity is about 3.9 J/g-K and water is ~4.2. On a volumetric basis, that pretty much gets canceled out though.
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Offline punatic

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Re: Does wort evaporate slower than water?
« Reply #5 on: December 01, 2013, 03:26:51 PM »
The heat of vaporization (boiling) of water is 2257 J/g.  Phase changes involve much more heat than raising and lowering the temperature of water within a phase.

Where did you find heat capacity for beer wort?  Is that for all beer wort, or does it change with the specific gravity of the wort?   ;)
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Offline a10t2

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Re: Does wort evaporate slower than water?
« Reply #6 on: December 01, 2013, 04:10:05 PM »
Where did you find heat capacity for beer wort?  Is that for all beer wort, or does it change with the specific gravity of the wort?   ;)

Just a rough number I've figured out from heating wort with an electric element. On a mass basis, it doesn't seem to vary much.
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