Boiler evaporation loss

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Boiler evaporation loss

Postby brewpete » Thu Jan 04, 2018 12:08

Hi, I have been brewing up to now using a 70 litre boiler with no lid and I have been using a figure of 8% per hour loss to evaporation. I have a new 200 litre boiler which does have a lid and a pipe outlet which is no more than a few inches in diameter. Clearly the loss to evaporation is going to be lower in this setup. Can anyone suggest a figure I might put in as a starting point?

Thanks
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Re: Boiler evaporation loss

Postby Saccharomyces » Thu Jan 04, 2018 16:11

Evaporation doesn't work on a percentage volume basis so you have to take a different approach.

The rate of evaporation depends mostly on the temperature of the wort, the surface area exposed to the air and the relative movement of the air or wort at the surface.

In lieu of further information, I'd take the current volume evaporated per hour and multiply it by the ratio of the exposed surface area of the vessels (bigger SA, more evap). If you wish to convert that back in to a percentage, then by all means do so, but it isn't the right thing from a scientific point of view.
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Re: Boiler evaporation loss

Postby brewpete » Thu Jan 04, 2018 16:37

Makes sense. What about the effect of the lid?
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Re: Boiler evaporation loss

Postby Eric » Thu Jan 04, 2018 19:29

brewpete wrote:Makes sense. What about the effect of the lid?


The lid will reduce the heat loss increasing the ferocity of the boil and could increase evaporation.
Losses also depends on input power. You've not said if that would be increased else it might not be possible to achieve a boil..
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Re: Boiler evaporation loss

Postby brewpete » Fri Jan 05, 2018 11:01

There are two 3kw elements in the boiler and I'm assuming that I will be able to switch one off once the boil is acheived.
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Re: Boiler evaporation loss

Postby Crastney » Fri Jan 05, 2018 11:56

if there's a lid on, the air movement will be a lot less, so evaporation will be a lot less, plus you get condensation which will fall back into the brew.
I was under the impression that the boil should be lid less to aid evaporation, and to ensure that you don't get condensate going back into the boil?...

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Re: Boiler evaporation loss

Postby robwalker » Fri Jan 05, 2018 12:52

Have you marked up your boiler with a sight glass bud? Easiest way by far, boil off remains fairly consistent, on a 6bbl I lose 0.1bbl every brew regardless of volume. It'll help you get the same OG every time for repeat brews too - extract wort, fill to 75% of target, take gravity sample, gravity / target x current volume = target volume then just liquor back.
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Re: Boiler evaporation loss

Postby Rolfster » Fri Jan 05, 2018 19:08

Crastney wrote:if there's a lid on, the air movement will be a lot less, so evaporation will be a lot less, plus you get condensation which will fall back into the brew.
I was under the impression that the boil should be lid less to aid evaporation, and to ensure that you don't get condensate going back into the boil?...


I think he said there is a hole in the lid that leads to an external vent.
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Re: Boiler evaporation loss

Postby brewpete » Fri Jan 05, 2018 19:29

Rob, no sight glass on the boiler unfortunately. It's a ready made system and it didn't come with one. The only sight glass is on the HLT (and that one is not marked).

Crastney, yes there is a vent in the top of the boiler.
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Re: Boiler evaporation loss

Postby INDIAPALEALE » Sat Jan 06, 2018 09:15

Fill the boiler to normal volume boil for normal boil length and measure the loss. Job done.

Crastney
If the condensate drops back into the boil it will be sterile so what's the problem.

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Re: Boiler evaporation loss

Postby robwalker » Sat Jan 06, 2018 09:39

INDIAPALEALE wrote:Fill the boiler to normal volume boil for normal boil length and measure the loss. Job done.

Crastney
If the condensate drops back into the boil it will be sterile so what's the problem.


DMS mostly i would say.
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Re: Boiler evaporation loss

Postby robwalker » Sat Jan 06, 2018 09:48

brewpete wrote:Rob, no sight glass on the boiler unfortunately. It's a ready made system and it didn't come with one. The only sight glass is on the HLT (and that one is not marked).

Crastney, yes there is a vent in the top of the boiler.


It'll pay you heavily to measure volume in MT and copper. When I mash in I start with 1300L, 50L to preheat, then 2.6L/kg grain and 30L underlet spare if needed, then you can measure your sparge each time, it's a good way to ensure consistency and makes life easier too.
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Re: Boiler evaporation loss

Postby INDIAPALEALE » Sat Jan 06, 2018 14:22

robwalker wrote:
INDIAPALEALE wrote:Fill the boiler to normal volume boil for normal boil length and measure the loss. Job done.

Crastney
If the condensate drops back into the boil it will be sterile so what's the problem.


DMS mostly i would say.


Using that theory I should not be brewing with a Braumeister :nono: Seems to work though :thumb:

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Re: Boiler evaporation loss

Postby Rolfster » Sat Jan 06, 2018 15:47

INDIAPALEALE wrote:
robwalker wrote:
INDIAPALEALE wrote:Fill the boiler to normal volume boil for normal boil length and measure the loss. Job done.

Crastney
If the condensate drops back into the boil it will be sterile so what's the problem.


DMS mostly i would say.


Using that theory I should not be brewing with a Braumeister :nono: Seems to work though :thumb:


It is also to do with the malts you use. Pilsner for example is know to give off DMS, but Maris otter is less prone.
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Re: Boiler evaporation loss

Postby brewpete » Mon Jan 15, 2018 10:17

For information, I completed a brew using my new boiler and the volume went from 188 litres pre boil to 184 litres post boil. That's just over 2% boil off over 90 minutes. Much lower than I expected!
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Re: Boiler evaporation loss

Postby fore » Mon Jan 22, 2018 23:17

Doesn't atmospheric temperature play a role? I ask because I'm quite well established, but my boil off rate seems to swing hugely. I'm starting to believe it's down to atmospheric temperature, and so recently started to record this as part of my brew day, to try and get a handle on it.
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Re: Boiler evaporation loss

Postby Brewzee » Tue Jan 23, 2018 07:37

That's an interesting point made me think of trying to make tea on my holidays by beach or in the mountains cos it makes a difference to how long it takes to get water to the boil. Also this discussion prompted me to experiment with a lid ajar approach to my last 2 boils, I agree about increased ferocity of boil but it did nothing to stop the wails of discontent from family members about smell and fog of brewing
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Re: Boiler evaporation loss

Postby Kev888 » Wed Jan 24, 2018 21:22

brewpete wrote:For information, I completed a brew using my new boiler and the volume went from 188 litres pre boil to 184 litres post boil. That's just over 2% boil off over 90 minutes. Much lower than I expected!

As you move to bigger volumes and lids, percentage evaporation may reduce. As the first reply mentions, that isn't necessarily relevant; the key thing is to check that you are getting an actual boil, with plenty of wort turbulence and movement around the kettle.

Some steam may condense on the lid and fall back in, but (obviously) water isn't bad for beer provided you account for the smaller gravity change during the boil, and the lid retains heat which is helpful for a more vigorous boil. The steam will also heat the lid, so DMS (which is more volatile) won't readily condense on it and return in the same way - water/volume and DMS loss aren't the same thing.

TBH I'm a little surprised the rate is quite so low though, is your kettle insulated fairly well?

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Re: Boiler evaporation loss

Postby fore » Sat Jan 27, 2018 15:55

So I have all but confirmed that ambient temp plays a BIG role. I brew outside. In the heat of summer (that's Alsace summer at about 32C), my highest boil off rate has been measured at 26%. Today I brewed at 9C ambient, with just under 14% boil off.

I have 2 elements, 2.5 & 1.5. When I really get a full handle on this, I might start to reduce to one element in summer.
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