Kettle Evaporation Rate

[Sammus]

Well, how much each did they pay?

They still effectively paid $9 each. The problem is the "add $2 the sales guy took" Now why would you do that? that $2 he took essentially increases the price of the case to $27, and it all works out fine and dandy. That is, the fact the refund was only $3 (as opposed to $5) already took into account that the clerk stole $2 (ie added $2 to the actual cost of the case, making it $27) Theres no reason to add it on again!

 

[kook]

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.

So say you've got a 98L kettle, and you're switching from a 60L batch to a 30L batch. Would you just gently simmer the 30L batch (so as to achieve the same evaporation percentage)?

Will the gentle simmering still cause enough break up of proteins etc as opposed to using a rolling boil? Doesn't it also help with hop isomerisation?

I realise that commercial breweries acheive a much lower boiloff (percentage wise), but most of their kettles are shaped to promote a continual, rolling boil.

Am I confused, or are you saying that it is much better to have a gentle, simmering boil (to reduce evaporation rates) rather than a rolling boil, as if the evaporation is exceeeding 15% you may have excessive maillard reactions?



edit - I've just re-read everything you've said, and I'm even more confused. It makes perfect sense if you're changing kettles for different sized batches (ie, wort surface area changes), but otherwise other than reducing the heat, how can you still acheive a rolling boil while maintaining a steady evaporation percentage?

 

[Screwtop]

They still effectively paid $9 each. The problem is the "add $2 the sales guy took" Now why would you do that? that $2 he took essentially increases the price of the case to $27, and it all works out fine and dandy. That is, the fact the refund was only $3 (as opposed to $5) already took into account that the clerk stole $2 (ie added $2 to the actual cost of the case, making it $27) Theres no reason to add it on again!

They Paid $30 ($10 ea) refund $5 ($2 for the salesman and $3 for the boys) so they paid $9 each = $27 and the $2 for the salesman = $29 your math is all wrong

 

[Sammus]

They Paid $30 ($10 ea) refund $5 ($2 for the salesman and $3 for the boys) so they paid $9 each = $27 and the $2 for the salesman = $29 your math is all wrong

I guess its a good exercise in logic if you haven't spent the past 6 years studying these kinds of problems... But believe me when I say this argument has a major flaw in it - the point where you add $2 of the refund onto the total amount paid, instead of taking it away like you do with $3 part. Now go and think about it a bit more - act it out with 3 friends if you want. Maybe then you can realise that people who research maths for a living don't tend to trip up on these often encountered logical paradoxes (I've seen it a several times before in different forms, I think it originated with people paying for a hotel room or something).

Think about it, you start with $30 thrown in. Then theres a $5 refund given. Why do you subtract 3 of those $5 from the $30, and add the other two?

Either keep track of all the money properly: subtract the whole five and end up with $25 to the boss, $2 to the sales clerk, and $3 to the customers.

Or you can look at from the sales clerks perspective: He gave them $3 change from $30, essentially charging them $27, which is $2 more than he needed to put in the till, so $25 in the till, $2 in his pocket. Still ends up being $25 = $30 - ($3 + $2) (Cost = Total - Refund).

Or you can look at it from my point of view: Hey look these 3 guys just paid $27 for a $25 case of beer, I wonder that extra $2 went that they paid? Oh it went to the slack ass sales clerk. Still ends up making sense.

Edit: I just realised you may be taking the piss out of me... I neglected to think about the "mustve miscalculated the % loss" statement that means u probably already know the solution... <_<

 

[Screwtop]

I guess its a good exercise in logic if you haven't spent the past 6 years studying these kinds of problems... But believe me when I say this argument has a major flaw in it - the point where you add $2 of the refund onto the total amount paid, instead of taking it away like you do with $3 part. Now go and think about it a bit more - act it out with 3 friends if you want. Maybe then you can realise that people who research maths for a living don't tend to trip up on these often encountered logical paradoxes (I've seen it a several times before in different forms, I think it originated with people paying for a hotel room or something).

Think about it, you start with $30 thrown in. Then theres a $5 refund given. Why do you subtract 3 of those $5 from the $30, and add the other two?

Either keep track of all the money properly: subtract the whole five and end up with $25 to the boss, $2 to the sales clerk, and $3 to the customers.

Or you can look at from the sales clerks perspective: He gave them $3 change from $30, essentially charging them $27, which is $2 more than he needed to put in the till, so $25 in the till, $2 in his pocket. Still ends up being $25 = $30 - ($3 + $2) (Cost = Total - Refund).

Or you can look at it from my point of view: Hey look these 3 guys just paid $27 for a $25 case of beer, I wonder that extra $2 went that they paid? Oh it went to the slack ass sales clerk. Still ends up making sense.

Edit: I just realised you may be taking the piss out of me... I neglected to think about the "mustve miscalculated the % loss" statement that means u probably already know the solution... <_<

:lol: no harm just fun intended Sammus, love to see simplicity explained in detail :lol:

But you can't deny the guys paid $27 for a carton of beer and the salesman got $2 thats $29. How, when the whole original $30 transaction consisted of $25 + $5 discount.

 

[Sammus]

:lol: no harm just fun intended Sammus, love to see simplicity explained in detail :lol:

But you can't deny the guys paid $27 for a carton of beer and the salesman got $2 thats $29. How, when the whole original $30 transaction consisted of $25 + $5 discount.

No denying your arithmetic is perfect, 27 + 2 = 29, no doubt in my mind there. And yeah, the guys paid $27 for a carton of beer, and the salesman got $2. It was not an extra $2 on top of the $27 though, it was part of the $27 in the first place.

I'm over it anyway lol

 

[Sammus]

Anyway, I digress!! (sorry people who didn't find it amusing )

My kettle evaporation rate is close to 20%, I can't get it lower unless I turn the burner down so low it ain't boiling anymore!

 

[Screwtop]

Anyway, I digress!! (sorry people who didn't find it amusing )

My kettle evaporation rate is close to 20%, I can't get it lower unless I turn the burner down so low it ain't boiling anymore!

On Ya Sammus enjoyed the joust. You must have a full opening on your kettle, yes?

I pretty much get 15.5% on 32.25L pre boil volume, depends on how hard I can get it boiling, some worts will froth and boil over more easily than others. Use a keg style boiler here with a 24cm hole in the top.

Screwy

 

[Thirsty Boy]

So say you've got a 98L kettle, and you're switching from a 60L batch to a 30L batch. Would you just gently simmer the 30L batch (so as to achieve the same evaporation percentage)?

Will the gentle simmering still cause enough break up of proteins etc as opposed to using a rolling boil? Doesn't it also help with hop isomerisation?

I realise that commercial breweries achieve a much lower boiloff (percentage wise), but most of their kettles are shaped to promote a continual, rolling boil.

Am I confused, or are you saying that it is much better to have a gentle, simmering boil (to reduce evaporation rates) rather than a rolling boil, as if the evaporation is exceeeding 15% you may have excessive maillard reactions?
edit - I've just re-read everything you've said, and I'm even more confused. It makes perfect sense if you're changing kettles for different sized batches (ie, wort surface area changes), but otherwise other than reducing the heat, how can you still acheive a rolling boil while maintaining a steady evaporation percentage?

The notion that the evaporation rate is independent of energy applied & the volume of liquid and dependent only on the surface area, is as far as I am concerned, based on the notion that your heat source is running flat out.. you are using a non adjustable electric element, or something like a turkey burner where its either all guns blazing, or nothing. If you have the capacity to put into the system, much more or much less energy than required to bring the volume to the boil, then that assumption no longer holds true.

For example: I can tell you for sure, that I get a MUCH higher evaporation rate out of my small kettle when its on my three ring burner, than I do when its on my stove... it geometry is the same and so is its surface area... so it must be the energy source.

When you increase volume, its more about the vertical height than volume I suppose, the heat and bubbles of steam lose energy to the liquid as they make their way to the top and the boil may not break the surface, So you have to shove in more heat to get the "vigor" up to a good level. So when you reduce from (in your example) 60l to 30l there is half the vertical distance, the heat can be turned down, the percentages will be roughly maintained and so will the vigor.

Thats the whole point... its not about maintaining a % figure.. let me emphasize... not about the figure ...its ALL about the vigor of the boil. The percentage figure is only a tool, that gives you a reasonable measurement of the vigor of the boil.. independent of the volume.

I keep repeating this sort of example.. I cant see how it is confusing

15% of 10litres is 1.5litres --- which is a nice rolling boil
15% of 100litres is 15 litres --- which is a nice rolling boil
15% of 200litres is 30litres --- which is a nice rolling boil

Its not an exact thing, 15% on your system is going to be different to 15% on mine... thats why there is a recommended range 8-15% that should give most homebrew systems (and many commercial ones) a nice rolling boil, safe in the knowledge that they are doing all the things that need to be done in a boil, but not boiling so hard that damage could be done.

As Andrew said, if you aren't willing to change your heat, or your lid arrangements, or even your kettle, then dont worry about it, you get what you get and have to live with it... And if you don't make large changes in the volumes you brew, then it just doesn't matter once you have established that your boil is at a reasonable level in the first place

I prefer to go to the extra trouble to alter my system, because I frequently alter my batch volumes. Otherwise I would just say 4 litres an hour too, which is what I get in my "standard batches"

If you are one of the people like Sammus who just cant get a boil at all without exceeding 15%.. then obviously you just have to... or you could try whacking on a lid or something, its pretty obvious that your system falls outside the parameters of the assumptions behind the theory.

I'm not trying to tell people that they should or shouldn't do anything at all... I was just trying to explain the purpose behind the use of a % figure when quoting recommended boil off rates. People seem to think that it is flawed... but its just a communication gap, they are using the % figure for the wrong purpose. Was just trying to fill that communication gap.

Thirsty

 

[Sammus]

Thirsty, FWIW I see your point and totally agree. And when I say 'can't get a boil' its more like...can't get what I think of as a rolling boil. I'm almost certain that peoples idea of a 'rolling boil' differ greatly. Which is why I guess we should be talking in % evap in the first place

Screwtop: I also use a CUB 'style' 50L vessel with the hole cut right to where the handles might be if it were at CUB keg.

I also use one of rambo burners that mashmaser sells. I like to hook it up to my BOC adjustable reg and watch it do its magic at 350kpa... not once its already up and boiling of course :unsure:

 

[Thirsty Boy]

. . . can't get what I think of as a rolling boil. I'm almost certain that peoples idea of a 'rolling boil' differ greatly. Which is why I guess we should be talking in % evap in the first place . . .

precisely

 

[kook]

Should a rolling boil not be visibly, "rolling"?

Maybe it's just my system then, but if I adjust my burner down on a smaller batch in my kettle to ensure the same evaporation rate, I only "simmer" the wort. I don't get a rolling action occuring unless I increase the heat.

Maybe as homebrewers we misinterpret the meaning of rolling boil?

 

[pint of lager]

Quite some time ago I found a definition of rolling boil for brewers to be about 25 mm difference between the peaks and troughs on on the surface of the wort.

 

[kook]

Quite some time ago I found a definition of rolling boil for brewers to be about 25 mm difference between the peaks and troughs on on the surface of the wort.

See thats what confuses me. If I was to boil that hard with say 10L in a 100L kettle, I'd probably get 50%+ evaporation in an hour. To reach 15% you'd need to simmer very gently.

Whilst this:

15% of 10litres is 1.5litres --- which is a nice rolling boil
15% of 100litres is 15 litres --- which is a nice rolling boil
15% of 200litres is 30litres --- which is a nice rolling boil

Sounds great in theory. It doesn't reflect what I've observed in practice. At least if a "nice rolling boil" is 25mm peaks and troughs on the surface.

 

[big d]

These days i tend to follow my refractometer readings during the boil and adjust accordingly.At times a simmer as described by Kook and other times to achieve my target i crank up the heat to achieve the 25mm peaks and troughs as described by Pint of Lager.

Cheers
Big D

 

[Thirsty Boy]

See thats what confuses me. If I was to boil that hard with say 10L in a 100L kettle, I'd probably get 50%+ evaporation in an hour. To reach 15% you'd need to simmer very gently.

Whilst this:

15% of 10litres is 1.5litres --- which is a nice rolling boil
15% of 100litres is 15 litres --- which is a nice rolling boil
15% of 200litres is 30litres --- which is a nice rolling boil

Sounds great in theory. It doesn't reflect what I've observed in practice. At least if a "nice rolling boil" is 25mm peaks and troughs on the surface.

But you have of course hit the nail on the head.. you probably couldn't boil that hard in a 100 litre kettle without getting a stupidly high evap rate.. this would be an indicator that if you want to brew 10litre batches, you are going to have to change something. (fairly drastically)

Remember I have been saying that changing the level of heat applied is just one of the things you can do.

If you were for instance to change to a different kettle size, more appropriate to the batch size, then you would find that you could get much closer to around 8- 15% per hour and be achieving the whole 25mm peak to trough delta.

Some sort of lid arrangement might do some of the trick, but probably not enough in the 10litres in a 100litre pot situation.

Or perhaps you could try a much smaller sized burner, and off set it to the side of your very large kettle. The wort would boil vigarously in a localised area of the kettle, and a circulation style current would be set up exchanging the whole volume of wort through the area of "vigor"

Or if you really wanted to get out there.. you could use the smaller (size not nec power), more localised heat source and introduce your vigor via a mechanical stirrer. The wort doesn't care how the vigor gets there, as long as its there.

Lots of different possible solutions.. the point is that because you are well outside the 8-15% range.. you are being given a strong hint that all isn't well and something needs to change. So you can go looking for those solutions. If you were in that range and the wort is actually boilng... then you can be reasonably confident that things are hunky dorey and you can just make some beer.

BTW: great reference POL... seems just about spot on to me.

Thirsty

 

[devo]

I recently managed to pull 20% evaporation on a 27lt batch after using a 50lt converted keg and my newly acquired Italian HP burner. I tell you what the boil was a tad more violent rather than a steady rolling boil so I think I may have to tweak it back a notch in future. <_<

I usually get around 11% when using my 100ltr ally pot.

 

[Ducatiboy stu]

I have also noticed that the weather has an effect on evap rates.

Can be a PITA sometimes

 

[apd]

This is bit OT but I was pondering the logistics of AG the other day and thinking what do the outdoors guy do if, say, an autumn leaf lands in the kettle! :unsure:

Same thing you do when an insect lands in there. Curse the little bugger and flick him out.

Although it helps if you can spot them going in there in the first place. I racked to secondary last night and discovered a little waspy thing stuck in the krausen ring. Best tasting beer out of primary I've ever brewed. Time will tell if the finished product stands up.

Andrew

 

[apd]

15% of 10 litres is 1.5lires/hour - a nice gentle rolling boil..
15% of 22 litrs is 3.4lires/hour - a nice gentle rolling boil..
15% of 45 litres is 6.75litres/hour - a nice gentle rolling boil..

The penny just dropped Thirsty. Thanks!

Andrew