Kettle Evaporation Rate

[warra48]

I venture to think that the humidity of your brewing environment will also have an impact on the rate of evaporation. The measured humidity in my home area is rarely less than 70% and often over 80%. Hence the capacity of the air to absorb more moisture is much less than say over in the Western Australia where the humidity is much lower. Then it must also be affected by the ambient air temperature, as cold air saturates at lower levels of moisture then warmer air.
I just stick with brewing all my batches to the same volume, and trust that my measurements remain fairly constant.

 

[LovesToBrew]

i like to work off a litre amount rather than %, i find i evaporate teh same amount whether my 70litre robinox is at 30 litres or 60 litres

 

[mudsta]

Ive got two different size elements in my setup.
I switch on both to bring to the boil and switch one off after hotbreak.

I use promash and keep my boils generally the same length of 75mins.
My boil off rate is 11.6%/hr with the one element going. Generally with the cals done at the start of boil I get within 500ml accuracy at the end of boil.

I'm about to upgrade to a new setup with gas heating and presume the accuracy will be less consistent.

I read somewhere a while back that commercial setups evap rate is in the range of 5 - 10%/Hr, thats why I only use one element instead of two (two puts me into the 26%/hr range)

Mudsta :beerbang:

 

[LovesToBrew]

that would give good control mudsta, i'm still trying to find a consistent settign with the gas burner

 

[MHB]

Boiling is a fascinating part of wort production - the evaporation rate is an important part of the process, but the one question that isnt being asked is "Why do the textbooks say we should be getting that 8-10% evaporation".

Primarily it's to remove Undesirable Hop Volatiles; if you achieve 8-10% loss as vapour you can be assured that the hop fractions you dont want in your beer will have been ejected.

Evaporation rates higher than 10% would serve no beneficial purpose and could have drawbacks, like accelerated darkening of the wort and excessive protein degradation.
They also consume more energy ($) and create a lot of steam that has to be dealt with.

Unless you are trying to make a very high gravity beer or are using monumental amounts of hops, enough heat to do the job is all you need.

From the above it is easy to understand why texts express the evaporation rate as a percentage.

Further on the moving air question:-
Vapour as it leaves the surface has just enough energy to undergo a phase change (liquid to gas). As the concentration of vapour in the atmosphere builds up, at some point it becomes supercritical (saturated) and a large portion of the vapour condenses and falls back into the kettle.

As we are trying to get rid of the hop volatiles (not the water) preventing the moisture concentration in the atmosphere above the surface from saturating will encourage the volatiles to leave and not be returned to the kettle with water vapour that is recondensing (i.e. when it does recondense it isnt over the kettle).

So yes a fan, draft or even a chimney can all help the evaporation rate.

MHB

PS
Why do paint drops dry as little circles, it is actually related.
Mark

 

[braufrau]

Ive got two different size elements in my setup.
I switch on both to bring to the boil and switch one off after hotbreak.

that's what I do too now.
There's so much hoo hah in internet land about hot break and the importance of
a rolling boil that I was boiling on two burners full bore for an hour and losing .... wait for it ...
50% of my wort!
That didn't seem right! :blink:
Don't know what it is now, but it looks about 15% and I feel much happier now and that's the main thing.

 

[mika]

Ding Ding ! We have a winner !

50% of your wort...I'd like to see that burner and that much steam ! :beerbang:

 

[mudsta]

The main reason for a massive boil off rate (i.e. heat input) is to clone the malliard reaction. Which trys to clone decoction mashing to a degree.

Bluntly, more browing of the sugars. See the master George Fix's books for this info.

The more water used in mashing just dilutes the end product and adds more energy expense in the boil.
We do need to boil to sterilize and drive off the nasties but their is a limit. 50% WOW!! that is beyond extreme.

Mudsta :beerbang:

 

[Thirsty Boy]

The purpose of a boil off rate is to aid in calculating final volumes in the boiler, using lt/hr rate I don't have to adjust my boil rate/vigour to come up with the same figure, I know I get 6lt evaporation everytime. Very simple and straight forward. I think the % rate is really for people that brew the same volume constantly and just makes the calculations more complex for those that brew varying sized batches.
I may have misunderstood the above comments but it seems you have contradicted yourself here. It looks to me like you Will have to vary the boil vigour based on your figures above in order to achieve the same evaporation amounts.

Cheers
Andrew

Sorry for the late reply to this Andrew, I hadn't seen your comment.

Yes, I think you have misunderstood. Almost completely I'm afraid.

I wouldn't be changing the boil vigor to achieve the same evaporation amounts. I would be changing the evaporation amounts (in litres per hour) in order to achieve the same level of vigor. This would give me a consistent evaporation rate expressed as a %

I do this by varying the amount of heat I apply to the kettle, perhaps putting a lid half on the kettle or by changing to a different kettle for very small batches, or some combination of the above.

And therefore (including reasons from my earlier post) I think exactly the opposite to you about the % figure. Boil of rate (%) isn't about calculating pre & post boil volumes, its about knowing that your boil is at the appropriate level of vigor and its mainly useful if you DO change your volumes significantly from brew to brew... If you are brewing roughly the same sized brew every time, then you just need to check it and play with your set-up till you have it in a reasonable range, then you can stop worrying about % and just calculate the L/hr figure that you always get.

Let me pose you a question.... You say that you get 6litres per hour everytime. What would you do if I asked you to brew me a 6 litre batch of beer?? Would you simply aim for a pre-boil volume of 12 litres and boil away half the wort? (braufrau might )

OR

Would you rightly think that doing that may well adversely effect the quality of the beer, and decide to change your pot/burner settings/lid/ etc etc so you could boil off less. How much less?? How much should you aim for??

Thats where the % figure comes in... I'd aim for 15% of the starting volume. I want to finish with 6litres, so that means a pre-boil volume of 7litres. So now I know that I need to fiddle with my system to the point where I get 1 L/hr boil off.


Now, brew me 500litres... still going to go with 1 l/hr ... of course not, how about 6... still probably not... but 15% = 88litres makes a bit more sense

See what I mean?

Thirsty

 

[Screwtop]

Sorry for the late reply to this Andrew, I hadn't seen your comment.

Yes, I think you have misunderstood. Almost completely I'm afraid.

I wouldn't be changing the boil vigor to achieve the same evaporation amounts. I would be changing the evaporation amounts (in litres per hour) in order to achieve the same level of vigor. This would give me a consistent evaporation rate expressed as a %

I do this by varying the amount of heat I apply to the kettle, perhaps putting a lid half on the kettle or by changing to a different kettle for very small batches, or some combination of the above.

And therefore (including reasons from my earlier post) I think exactly the opposite to you about the % figure. Boil of rate (%) isn't about calculating pre & post boil volumes, its about knowing that your boil is at the appropriate level of vigor and its mainly useful if you DO change your volumes significantly from brew to brew... If you are brewing roughly the same sized brew every time, then you just need to check it and play with your set-up till you have it in a reasonable range, then you can stop worrying about % and just calculate the L/hr figure that you always get.

Let me pose you a question.... You say that you get 6litres per hour everytime. What would you do if I asked you to brew me a 6 litre batch of beer?? Would you simply aim for a pre-boil volume of 12 litres and boil away half the wort? (braufrau might )

OR

Would you rightly think that doing that may well adversely effect the quality of the beer, and decide to change your pot/burner settings/lid/ etc etc so you could boil off less. How much less?? How much should you aim for??

Thats where the % figure comes in... I'd aim for 15% of the starting volume. I want to finish with 6litres, so that means a pre-boil volume of 7litres. So now I know that I need to fiddle with my system to the point where I get 1 L/hr boil off.
Now, brew me 500litres... still going to go with 1 l/hr ... of course not, how about 6... still probably not... but 15% = 88litres makes a bit more sense

See what I mean?

Thirsty

Thirsty it's all related to scale and economy of scale in brewing is no different. If the whole system were scaled up or down to suit the nominated value of wort then all things would be equal would they not. If I boiled a small batch in my boiler I would not achieve the 15.5% that I always get with a 32.25L (pre-boil) batch. Percentages should work fine irregardless of scale but in the physical world (read physics) many other variable come into play, fixed math principals apply at a much more basic level. Greater than 10% boiloff in a 200CL kettle to ensure removal of undesirable Hop Volatiles or for Malliard reactions or for whatever reason is far different to what percentage may be required to achieve the same desired result using a 50L kettle. But that ****'s far too deep, lighten up I say.

How about this.

3 guys pitched in $10 each to buy a $30 carton at the bottlo. They'd just walked out as the manager advised staff that the cartons had been dropped by $5 for an hour as a promo special, go and give them $5 back he said. Well the staffer thinks dividing $5 between three is too hard and sees a way to make a couple of bucks, so pockets $2. Outside the bottlo he apologises and says the cartons were on a quickie special giving each of them $1. They were surprised at the honesty and went away happily to be repeat customers of that business. But how much did they pay for the carton, originally $10 each then they each received a refund of $1 so they paid $9 each that's $27 add back the $2 pocketed by the sales person and the total is $29 so where did the other dollar go. Must have miscalculated the % loss

BF: I don't think I could boil hard enough to achieve 50% loss, well maybe I could, but I'd end up mopping most of it up off the floor after the boil over.

 

[ozpowell]

I wouldn't be changing the boil vigor to achieve the same evaporation amounts. I would be changing the evaporation amounts (in litres per hour) in order to achieve the same level of vigor. This would give me a consistent evaporation rate expressed as a %

Thanks for conveying this so succinctly Thirsty! Makes perfect sense to me now - scary :blink:

I've been struggling with this exact question recently as I'm about to do my first half batch.

Cheers,
Michael

 

[AndrewQLD]

I wouldn't be changing the boil vigor to achieve the same evaporation amounts. I would be changing the evaporation amounts (in litres per hour) in order to achieve the same level of vigor. This would give me a consistent evaporation rate expressed as a %

I'm not sure if I follow this at all, wouldn't changing the amount of heat also change the boil vigor?

I do this by varying the amount of heat I apply to the kettle, perhaps putting a lid half on the kettle or by changing to a different kettle for very small batches, or some combination of the above.

And that is my point, if you do a 24 lt boil and a 30 lt boil you will have to stuff around getting a lid on the boiler in the right spot or the flame on your gas at the right level or heaven forbid a different size pot so you can get your percentage figures the same for both batches. I don't need to do any of that.

I tend to go about it differently,
I don't put a lid on the kettle.
I don't adjust my burner/ boil vigor.
I don't change pot size.

I rate my boil off as lt/hour because that is a constant figure of six lt. If I boil 24 lt or 30 lt it is still 6lt/hour.
And that is how I like it easy and simple, I know exactly how much wort I need preboil and exactly how much I will get post boil because my evaporation rate is a constant 6lt per hour.

I can see what you mean as far as percentages are concerned and smaller batches ie 6lt, but that would be totally inapplicable to me and so I don't worry about it.

Thirsty, your method/system works for you just as well as mine works for me, but I prefer mine for it's simplicity.

Cheers
Andrew

 

[ozpowell]

I'm not sure if I follow this at all, wouldn't changing the amount of heat also change the boil vigor?

Hey Andrew,

I think Thirsty's point (or at least the way I understand it) is that for different boil volumes, you need different amounts of energy to maintain the same level of boil vigor. And a constant boil vigor == a constant % evaporation.

Seems to make some sense to me (Disclamer - I'm a software engineer, not a physicist, so I could be totally wrong )

Cheers,
Michael

 

[AndrewQLD]

Hey Andrew,

I think Thirsty's point (or at least the way I understand it) is that for different boil volumes, you need different amounts of energy to maintain the same level of boil vigor. And a constant boil vigor == a constant % evaporation.

Seems to make some sense to me (Disclamer - I'm a software engineer, not a physicist, so I could be totally wrong )

Cheers,
Michael

Hi Michael,
But I don't see that on my system though, 2 ring burner flat out gives me 6lt evaporation from a 20lt or 40lt of wort. Perhaps this is a system/equipment specific thing, either way it doesn't really matter so long as you get the results you want.

Cheers
Andrew

 

[ozpowell]

Hi Michael,
But I don't see that on my system though, 2 ring burner flat out gives me 6lt evaporation from a 20lt or 40lt of wort. Perhaps this is a system/equipment specific thing, either way it doesn't really matter so long as you get the results you want.

Cheers
Andrew

I'm going to do a half batch soon on my equipment, so I'll update with my results....

Cheers,
Michael

 

[Sammus]

How about this.

3 guys pitched in $10 each to buy a $30 carton at the bottlo. They'd just walked out as the manager advised staff that the cartons had been dropped by $5 for an hour as a promo special, go and give them $5 back he said. Well the staffer thinks dividing $5 between three is too hard and sees a way to make a couple of bucks, so pockets $2. Outside the bottlo he apologises and says the cartons were on a quickie special giving each of them $1. They were surprised at the honesty and went away happily to be repeat customers of that business. But how much did they pay for the carton, originally $10 each then they each received a refund of $1 so they paid $9 each that's $27 add back the $2 pocketed by the sales person and the total is $29 so where did the other dollar go. Must have miscalculated the % loss

hehe the maths is all wrong here. It's good food for thought though. Upon close inspection your just basically adding/taking away any old number that came up in the story.

 

[Sammus]

Hi Michael,
But I don't see that on my system though, 2 ring burner flat out gives me 6lt evaporation from a 20lt or 40lt of wort. Perhaps this is a system/equipment specific thing, either way it doesn't really matter so long as you get the results you want.

Cheers
Andrew

maybe your burner is only capable of putting in so much energy, and that limit peaked at your 20L batch. You need a certain % evaporation to get rid of certain hop volatiles and whatnot. given that you've met and exceeded those values, the rest is just a waste of energy. The point is you could turn your burner way down for your 20L batch and still observe the required evaporation (ie to get rid of hop volatiles and whatever, no for beersmith to calculate your efficiency )

 

[ozpowell]

Well wadda ya know. Here I am reading my latest BYO mag and what do you think this edition's Advanced Brewing topic is? A discussion of aspects of wort boiling.... Here's a few quotes that I think add an interesting twist to this discussion:

The amount of evaporation varies with the size and geometry of the kettle, the surface area exposed to the air, the intensity of the heat source and to a lesser extent other variables such as the ambient temperature, humidity, air pressure and any movement of are surrounding the kettle.

and

For homebrew size batches (5 - 15 gallons/19-57L), the evaporation rate is normally measured in gallons (or liters) per hour, with typical values of 1 to 1.5 gallons (3.8 to 5.7 L) per hour.
...
Measure the volume both at the beginning and end of the boil and calculate the difference. Divide by the boiling timein hours to determine the evaporation rate.

For example, if the beginning volume is 7.5 gallons (28L), the ending volume is 5.5 gallons (21L) and the boiling time is 90 minutes, the evaporation rate is 1.33 gallons (5L) per hour.
...
Assuming the same kettle and burner are used, and that they are capable of maintaining an adequate boil, the boiling losses are largely independent of the batch size because the major factor is the surface area.

Finally, in relation to boiling the wort covered vs. uncovered:

...
DMS is undesirable in nearly all beer styles. Fortunately, DMS is volatile, and a vigorous boil evaporates it and drives it off into the air with the steam. ... For this reason it's important to leave the kettle mostly uncovered during the boil so the steam does not condense and return to the wort.

:blink:

Cheers,
Michael

 

[Tony]

exactly !

cheers

 

[Screwtop]

hehe the maths is all wrong here. It's good food for thought though. Upon close inspection your just basically adding/taking away any old number that came up in the story.

Well, how much each did they pay?