Poll: What's Your Evaporation Rate?

[Fourstar]

approx 15% p/hour with around 1-1.5L of loss of trub in the kettle.. higher loss for flowers/plugs or a highly hopped beer 150g+ in 23L.

 

[rich_lamb]

I'm still trying to figure out how using a % of kettle volume can possibly give me a relevant number (that can be used as a basis of comparison). I use a 50L kettle and consistently get evap loss of 4.5L/hr.
So that would be about 9%, which is kindof a pointless number since I typically boil about 24-27L or wort (closer to 20%).

I'd be far more interested in the absolute value; and it seems most people have been good enough to publish that. It might also be worth listing the kettle type to see if that affects the evap rate. Mine is a SS keggle, which I feel boils quite poorly, and I've often thought a big Ali pot would do a better job.

 

[Thirsty Boy]

Evaporation percentage rates don't work. Boiloff rate for my system is usually 6L per hour.

Screwy

Of course they do - they just aren't for what people think they are for.

The boil off rate in % is to let you know a bit about your level of boil vigor and to let you know whether you have atually evaporated enough to carry away all the volatiles etc that need to be gotten rid of.

Say I do a 25L batch and I boil off 2.7L per hour. Thats 11% of my starting volume and thats right in the middle of the rates that are accepted as being acceptable in order to ensure the quality of your beer.

Great - so now I want to make a batch starting with 45L - my kettle is a 50L keg - so it will fit. And I boil off 2.7L per hour. So I can do all my calculations and know I will get 42.3 at the end of the boil.

sweet - right?? So who the hell needs the % figures for boil off. They are obviously of no use to anyone and should be ignored

Except that now - if I do look at the % figure - I am only boiling off 6% of my starting volume - and there is a goodly chance that I will not have evaporated all the bad out of the beer. Its also possible that there wasn't enough heat in the system to give me a good hot break, or utilise my hops fully etc etc.

Now if I turned my burner up a bit higher - got the wort jumping around a bit more (which effectively increases the surface area) and managed to up that figure by a litre or so (up to 8%) - then I am back into the comfort zone of the generally accepted figures. Anyone who says you cant do it is full of the proverbial. A strong, very active boil will evaporate more than a gentler boil. Pot surface area is the most important factor, but its not the only one.

So - different figures for different purposes. L/hr lets you do your numbers. Its about starting and finishing volumes.

% of starting volume per hour is about whether you L/hr figure is high enough in the first place (or maybe too high) - and whether you should consider changing something about your system to get your boil to a point where you know its doing everything it should be doing.

 

[KHB]

I lose 5lt in boil off whether im doing a single or a double batch consistently.

Scotsman06

 

[mckenry]

Of course they do - they just aren't for what people think they are for.

The boil off rate in % is to let you know a bit about your level of boil vigor and to let you know whether you have atually evaporated enough to carry away all the volatiles etc that need to be gotten rid of.

Say I do a 25L batch and I boil off 2.7L per hour. Thats 11% of my starting volume and thats right in the middle of the rates that are accepted as being acceptable in order to ensure the quality of your beer.

Great - so now I want to make a batch starting with 45L - my kettle is a 50L keg - so it will fit. And I boil off 2.7L per hour. So I can do all my calculations and know I will get 42.3 at the end of the boil.

sweet - right?? So who the hell needs the % figures for boil off. They are obviously of no use to anyone and should be ignored

Except that now - if I do look at the % figure - I am only boiling off 6% of my starting volume - and there is a goodly chance that I will not have evaporated all the bad out of the beer. Its also possible that there wasn't enough heat in the system to give me a good hot break, or utilise my hops fully etc etc.

Now if I turned my burner up a bit higher - got the wort jumping around a bit more (which effectively increases the surface area) and managed to up that figure by a litre or so (up to 8%) - then I am back into the comfort zone of the generally accepted figures. Anyone who says you cant do it is full of the proverbial. A strong, very active boil will evaporate more than a gentler boil. Pot surface area is the most important factor, but its not the only one.

So - different figures for different purposes. L/hr lets you do your numbers. Its about starting and finishing volumes.

% of starting volume per hour is about whether you L/hr figure is high enough in the first place (or maybe too high) - and whether you should consider changing something about your system to get your boil to a point where you know its doing everything it should be doing.

Thanks Thirsty, That all makes good sense
But herein lies the problem for us new to Beersmith.
I know I boil off 9L per hour. I have a recipe for final volume of 35L. I know at my 21% figure I need to have a pre boil volume of 44L. Beersmith also works this out using my 21% figure.
As has been stated - 9L/h is constant.
As a test, I halved my final volume to 17.5L. I would want to have a preboil vol of 26.5L but beersmith works it out for me as 23.4L (roughly) based on 21%. So whats a beersmith newbie to do? Every time I change volumes do I need to untick the 'Set boil volume based on equipment' box and add 9L to the batch size and let beersmith work out the new sparge water volume for me? Is this the go? Or is there a way of setting 9L/h as the constant for beersmith formulations instead of the evap rate?
cheers for your help.
mckenry

 

[Screwtop]

Thanks Thirsty, That all makes good sense
But herein lies the problem for us new to Beersmith.
I know I boil off 9L per hour. I have a recipe for final volume of 35L. I know at my 21% figure I need to have a pre boil volume of 44L. Beersmith also works this out using my 21% figure.
As has been stated - 9L/h is constant.
As a test, I halved my final volume to 17.5L. I would want to have a preboil vol of 26.5L but beersmith works it out for me as 23.4L (roughly) based on 21%. So whats a beersmith newbie to do? Every time I change volumes do I need to untick the 'Set boil volume based on equipment' box and add 9L to the batch size and let beersmith work out the new sparge water volume for me? Is this the go? Or is there a way of setting 9L/h as the constant for beersmith formulations instead of the evap rate?
cheers for your help.
mckenry

mckenry, depends on which school you belong too, some don't advocate anything more than 5% boiloff rate so don't sweat this issue. Anyway my workaround in beersmith is to simply work with whatever pre-boil volume and adjust the percentage in Beersmith until the loss equals the known rate for my system.

Hope this helps,

Screwy

 

[mckenry]

mckenry, depends on which school you belong too, some don't advocate anything more than 5% boiloff rate so don't sweat this issue. Anyway my workaround in beersmith is to simply work with whatever pre-boil volume and adjust the percentage in Beersmith until the loss equals the known rate for my system.

Hope this helps,

Screwy

OK. Pity there isnt a section that you can check or uncheck the L/h or % evap for beersmith to work with to give you required water volumes.
Guess your way or my suggested way are just different ways of skinning the same cat.

 

[peas_and_corn]

Bumping this thread instead of starting a new one.

In the most recent issue of BYO, Mr Wizard says that an evaporation rate of 20% is somewhat excessive. His reasoning is that it can make a beer darker than it should (if you're aiming at making something pale it can be an issue) and that it "is likely lending some flavours that would be good to not have".

So, do you agree with this claim? If so, what sort of flavours would be added in with an excessively high evaporation rate? What would I look for when drinking one of my beers that would indicate that the boil has a too high evaporation rate?

 

[MarkBastard]

I wouldn't have a clue to be honest. I just now know what I need to start with to get 20L of wort in a cube.

 

[Thirsty Boy]

Once again - its not the rate which is all that important in that argument - its the vigor of the boil. Mr wizard assumes that to get the 20% mentioned you are simply shoving in too much heat and so your boil is too active. You would be looking at darker beer, perhaps more malt and caramel type flavours. All OK in a robust type ale, not so much if you are looking for a delicate light lager type beer.

You can also potentially damage head formation, clarity and stability of your beer by boiling too hard - not to mention simply wasting a crapload of gas.

But thats all about boiling too hard - not about evaporation rate. Because as the rest of this thread mentions, the biggest influence on evaporation rate is pot surface area. So if you happen to have a low wide pot, or to be boiling your 20L batch in your 100L pot... then you are probably getting a giant boil off rate, but you aren't necessarily shoving in too much heat or boiling too hard. You probably are - but not necessarily.

All the figures people quote (me included) generally assume you have a brew kettle somewhere around the rough ideal of twice as wide as your wort will be deep. So for example - if your starting volume is 25L, then a brew pot with 40cm diameter is perfect. In a 40cm diameter pot the depth of wort for 25L is 20cm. So you have the 2:1 ratio. In that case, or close(ish) to it - the % boil off rates recommended, will match reasonable L/hr figures, will match good boil vigor.

So when people talk about boil off and evaporation - you need to keep that assumption in the back of your mind. It might not apply to you. Of course.. if it doesn't, you need to ask yourself if you have an appropriately sized pot?

 

[Nick JD]

Depends a lot of whether I suddenly sit up off the couch and say, "SHIT! The homebrew."

And in the bottom of the pot is about 8 liters (started with twice that of 1.065) of really dark, half caramelised wort with a hop bag half-dangling off the side that's been boiling for about two and three quarter hours.

Damn it if it didn't turn out to be an exceptional beer...