6%/h Enough Evaporation?

[Trent]

Hey guys
Got a strange little problem that I hope someone can help me with. I have recently started doing double batches, today was my second. My first one on my new system had me 2 points shy of my target gravity, but 4L over my target volume. Today, I hit my target gravity, but was again, 4L over volume. I am pretty sure I didnt mess up my volume calcs, so about 60.3L went into the boil kettle, I did a 90 min boil after it finally started (gotta get me a nasa burner, over an hour to reach boil from 65C is a bit much!), it was a rolling boil, and I syphoned out to my fermenter, took 4L for priming with when I am bottling, then got 47L into the fermenter, and 3.2L left with the trub in the kettle. I know, because in an effort to find out my evap rate, and solve this bloody puzzle, I pulled it all out with a measuring jug (too much hop trub to siphon :huh. So, that is 60.3 - 54.2 over 1.5 hrs, is about 6.6% evap per hour. I know that most people aim for 10-15% per hour, and in the same boil kettle for my 23L batches, I consistently got about 10% per hour. It is an old 18 gallon keg, legally acquired, and the opening is about 25cm in diameter. I boil with the lid completely off. Basically, at the end of the day, it makes no difference to me, and I can allow for such a little evaporation, but I am worried that the volatile compunds that need to be boiled off may not be making their way out, so I am more than anything concerned for the long term flavour and stability of my beers. I am using a 3 ring burner with a normal bbq type reg, and it seems to struggle, if I had a bigger burner, would I achieve my usual 10% evap, or should I just adjust my calculations to suit 6.6%/hour?
Thanks for any advice
All the best
Trent

 

[Guest Lurker]

Sounds like you got exactly the right evap. The problem is you are using evaporation rate as a percentage of batch size.

I really dont know why the default in Promash is to set evap to percentage. Evaporation rate is pretty much constant for any system in l/hr. So, if like me, you do different batch sizes, you should set evaporation to rate per hour, and the use the same for all batch sizes. Evaporation rate is a function of the vigor of the boil, the open area of the kettle, and the rate of air flow across the top of the kettle. None of which are changed by the volume in the kettle.

The only very slight difference would be that evaporation is less from a high gravity solution. For example evaporation rate from seawater is less than from fresh water in the same conditions. Buts its a small effect and so I still dont understand why you even have the option to set evaporation as a percentage.

Set it as a constant rate.

 

[MHB]

Hi Trent
The reason for the 8-10% / hour evaporation rate is to remove undesirable hop fractions. Volatile hop fractions are best gotten rid of by a vigorous boil, I would look at up sizing the reg, the burner reg combination you have is nearly big enough, but a better reg will let you control the burner better and give you a lot more heat.

I have made barley wine and wanted to concentrate the wort, directing a small fan over the kettle, with a vigorous boil, got the evaporation rate up to nearly 20% / hour.

This isnt a substitute for a full on boil.

MHB

 

[Trent]

Thanks GL
That makes a hell of alot of sense. It wasnt a high gravity beer (it is actually my first mild), but thinking back to most of my other beers, it is probably around 3.5-4L per hour loss, which is about what I got this time. I will set it for 4L/Hr and go from there.
I love this site, just about any question ya could come up with is answered pronto!
All the best
Trent

 

[Trent]

Looks like we posted at the same time, Mark
Good to see ya online. I am probably gonna get a bigger burner and reg after xmas, like you suggest, but between now and then, will work on the 4L/H.
Will be down around xmas for a beer!
All the best
Trent

 

[warrenlw63]

Trent.

When I did 40 litre batches in a 50 litre keg I would boil with the lid partially over the opening to deliberately reduce the evaporation rate and turn down the burner. While it's not deemed a proper practice the resultant beers were fine, if not very good. :beerbang:

I initially obsessed about the condensation off the lid dropping back into the boil. Then I thought bugger it, it's only really water. Anything that's deemed volatile would most likely channel out into the outside air. :unsure:

Also worth noting that your efficiency seems to automatically improve with larger batches. Why? No bloody idea. :blink:

Warren -

 

[T.D.]

I think the vigor of the boil will affect the evaporation rate. I use a 2400w immersion element. It holds a rolling boil well, but I would definitely not call it vigorous. from a 25L boil volume, I lose about 2L over a 60min boil (takes about 30-40mins to get it to the boil too). So that's about 8%, not including pre-boil evaporation. Probably works out to be quite similar to your result Trent. I would tend to put it down to the lack of vigor in the boil.

 

[Ross]

Also worth noting that your efficiency seems to automatically improve with larger batches. Why? No bloody idea. :blink:

Warren -

[post="92026"][/post]​

Warren,

I assume it would be because you are sparging with a larger volume of water, though I guess that should only make a difference with fly sparging?...

 

[T.D.]

Also worth noting that your efficiency seems to automatically improve with larger batches. Why? No bloody idea. :blink:

Warren -

[post="92026"][/post]​

Warren,

I assume it would be because you are sparging with a larger volume of water, though I guess that should only make a difference with fly sparging?...

[post="92032"][/post]​

Ross, but there is also more grain to be rinsed. The sparge water volume does increase, but to my knowledge it does so proportionately.

 

[warrenlw63]

Ross.

Was a fly sparger. Up until the last brew. Now a converted batch sparger. :beerbang:

Oddly enough my efficiency wound up identical to fly sparging. :unsure:

Warren -

 

[Borret]

T.D

I understand what Ross is saying here. Due to double the batch size with the same tun the cross section of grain is the same, just twice as high, so the volume of sparge water that passes past each grain is double giving more chance for better rinsing. (only applies to the fly guys) The downfall again is that the same cross section of grain at the top of the bed that would usually be have the benefit of less sparging to reduce extraction of nasties now has twice as much sparge water going past it.

So you could change the dynamics (proportion) of your tun on a standard batch so the grain bed was twice as deep/ half the cross section, and it would have the same effect.

Hope that makes sense.

Borret

 

[T.D.]

That makes much more sense, thanks Borret.

 

[Trent]

Warren
I have defineitely noticed that my efficiency has gone up, but it will be a few more batches before I can accurately predict it. I am working on 75%, my first double batch got 76%, and the one yesterday I got 80%. My old system I was only getting 65-70%, so I am pretty happy. I am batch sparging, and running 2 lots of sparge water through, makes for a longer brew day, but only by half an hour, and I am happy for that to make sure I hit 75%. Besides, once I add my bittering hops, I usually run down to the beach for a quick dip, so its not all standing by the brewery!
All the best
Trent