evaporation rate (boil off)

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evaporation rate (boil off)

Post by paulg » 4 years ago

I completed my first brew with my new 70 litre pot today.
the pot has a 45 cm diameter and a 4500 watt electric element.
I used biabacus spread sheet which predicted a 10.21 litre loss to evaporation for 90 minute boil.
If my measurements are correct I actually lost 13.47 so about 9 litres per hour,is this a typical loss for a pot of this diameter? ,my boil didnt seem excessively hard and was boiling at about 98 c as i live at 650 meters above sea level.
I had my pid set to 99 but the temperature only rose that high when I partially covered the pot and then it nearly boiled over.
I actually exceeded gravities and due to not so much loss for kettle trub and adding 3 litres to the fermenter to lower OG. I got 25.5 litres at the required OG .I was aiming for 25 so happy about that.
any comments please,I am thinking next time just adjust evaporation setting on biabacus and all should be well
thanks Paul


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Post by joshua » 4 years ago

PaulG,

Does BIABACUS have a place to enter your Alitude and Barometric pressure???? I don't think so.

SO, Your boil off temperature may have as low as 98C, so you can boil off about 108% per hour of the volume the program stated.....Opps, Sorry PP.

But, You can Add some GOOD water to dilute the "GIV" gravity into the fermenter, to get the gravity you Want to have, or the Volume into the Fermenter(VIF)!!
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Post by paulg » 4 years ago

when I checked on a calculator at my high above sea level boiling point is indeed about 98 c.
however whether it also affects boil off rate I dont know that was the point of my post ,although maybe I didnt make it very plain.i was hoping someone more knowledgeable than me might chime in with some answers
and yes that was what the 3 litres added to fermenter was for to dilute to required OG


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Post by joshua » 4 years ago

PaulG, What I was thinking, is depending on the Energy(4500watt), the diameter of your kettle, the Humdity, Ambient temperature, and Barometric Pressure, you boiling temperature can vary from 97C to 102C depending where you live and what the weather is like.

The higher the Boil temperature will decrease what you can boil-off from the power you have, and conversely, the Lower boil temperature will Increase the Boil-off rate a lot.

Where I am Located, I CANNOT ever hit the Predicted/projected boil off amount over the last 70 brews.

Always too high, or Too low.

Sorry, I can't give you a number because it can change daily.
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Post by paulg » 4 years ago

thanks joshua
as I said in my first post I was pleased with the final result and can top up or boil slightly longer to get the correct og or brew length.
I now realise my boil off is probably about right not to fierce a boil which was what I wondered.I will try and adjust the boil off on the baibacus next brew day and keep records each time and maybe I can get a bit nearer but if not does it really matter(I think not as it is easily rectified)
Paul


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Post by PistolPatch » 4 years ago

I have the same capacity and diameter kettle Paul. My boil-off varies from brew to brew depending on the weather etc so maybe wait a few brews before changing the BIABacus default too much. As josh has pointed out, a lot of things can affect the rate on any one day. I always prefer having to use a bit of top-up water at the end rather than the reverse so under-estimating evap rate is better than over-estimating it.

:peace:
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Post by paulg » 4 years ago

yes fully agree PP it is easier to top up than to boil for longer.
It was just the boil off seemed 50 % more than predicted .
I never know what is a good rolling boil and what is too much.I had it so that the middle of the pot was boiling and then flowing towards the sides .This is my interpretation of a rolling boil but I have seen boils with the surface frothing and churning like crazy, and wondered is this what i should be aiming for.


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Evaporation rates variance

Post by PistolPatch » 4 years ago

On the rolling boil thing, what you are describing sounds great Paul. You don't want a simmer going on nor do you want the wort jumping out of the kettle.

Going back to whether you should adjust your evaporation rate. Here's why I reckon, "No!"

As with anything in brewing, you can't trust the numbers on one brew. Evaporation numbers can vary wildly. Here are the evaporation rates in litres for 1.5 hours on 6 brews of mine done over three consecutive days...

9.0 L / 15.1 L / 9.3 L / 9.6 L / 8.0 L / 7.2 L

So what does that tell me? The main thing it tells me is that a single brew's measurement can tell you nothing much at all ;). For example, perhaps I made a measurement error on the second brew - who knows for sure? See how the last two brews had less evaporation than the first four? The last two brews were done on calm days not windy days like the first four brews.

The final thing that the collection of numbers tells me above is that the BIABacus default works almost perfectly for my kettle - on average. Until you have such a collection, over-riding any defaults is probably not going to serve you well.

:peace:
PP
Last edited by PistolPatch on 30 Mar 2013, 01:50, edited 2 times in total.
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Post by paulg » 4 years ago

thanks PP
I had already decided to leave well alone for the time being re biabacus settings.
that 2nd brew of yours is deffinately very different to the others in terms of boil off??


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Post by HbgBill » 4 years ago

IF, IF there was a way of honing in on your propane flame so that it is EXACTLY the same each time you adjust it.. numbers would be closer. I played with this with both my experimental water only boil as well as my first BIAB. One of my burners has a main on/off valve on top of the tank.. followed by a regulator. After the regulator is a small needle valve. I have found that MINUTE adjustments of this can bring the wort from simmer to heavy rolling. Backing to a reasonable rolling boil takes care. While I haven't experimented with different boil-off's, my plan is to simply go by a 'visual' and 'about' where the needle valve is placed.. short of a 'flow control'.. this is the best for me.

I just bought a used Blichmann burner and it only has an adjusting valve on top of the regulator. The burner itself is HUGE. It'll be awesome for larger boils.. and I'll play with it for my next small batch.. the burner seems VERY WELL made. I'm thinking I'll really have to learn the valve on that one to avoid both burning off a ton of propane and/or boiling off a lot of my wort.

Anyhow, I believe the result of my experience is paying close attention to where the valve is. With the Blichmann, I'll probably take a felt tip pen and make a mark on the regulator body to show here the valve should be for optimum boils. It'd be all too easy to say this is where I think it was last time and over/undershoot the best for the volume of boil. Agreed, other factors such as air pressure, humidity, etc will play a factor.. but, for now.. I'll concentrate on the valve positioning.
Bill
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Post by PistolPatch » 4 years ago

paulg wrote:that 2nd brew of yours is definately very different to the others in terms of boil off??
It is a wide discrepancy on that brew. Probably a measurement error of some sort as I did 6 side by side double batches in those three days recording many sets of measurements for an experiment. With that many numbers, you'll always get some wild figures. It also was an IPA so the larger hop bill had a little bit to do with that measurement discrepancy I believe - long story.

Mind you, I still get some wild figures occasionally no matter how accurately I think I have measured and double-checked. This is why I never trust anyone that says they always hit all their numbers dead on. Even if you could measure perfectly, there should be variance between brews as water, weather and grain extract potential will all vary from day to day or batch to batch. The most amazing brewers are those who always get the same 'efficiency' regardless of whether they are brewing a 1.040 beer or a 1.060 beer.

Posts like that are claiming the impossible. It's a common belief that you will be able to brew consistently and always hit your numbers in home brewing but it's just not the case. Even the largest commercial breweries have to make adjustments from brew to brew to correct for inconsistencies in ingredients etc. Our inconsistencies should be much greater.

:peace:
PP
Last edited by PistolPatch on 30 Mar 2013, 02:49, edited 2 times in total.
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Post by HbgBill » 4 years ago

OhOh.. I hit my numbers pretty exactly on my first (and only.. so far) BIAB. So, I guess you don't trust me :think: But, that's OK. I did, none the less. Next time is anyone's guess. :party:
Last edited by HbgBill on 30 Mar 2013, 03:28, edited 2 times in total.
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Post by PistolPatch » 4 years ago

:lol: Bill. If it happens ten times in a row then I won't trust you :nup:.

And don't worry, you are not alone in getting right numbers ;). I just wrote in another thread that the BIABacus auto-estimates for evaporation, trub/s and efficiency/s seem to be getting most brewers in the ball-park if not hitting a home run like yourself. That's a pretty good thing. Having good numbers to work from in the beginning is the first step.

The next step, I think, is to learn not to worry when you don't hit your numbers.

For example, if your into fermentor numbers didn't hit on a single brew, you'll never know whether there was really a problem unless you took some pre-boil and/or EOBV numbers as well.

If you had taken those 7 measurements (pre-boil volume and gravity / end of boil volume and gravity / volume into fermentor, kettle trub volume and fermentor gravity) then you will be ahead of the other brewer as you will have a series of double checks and therefore know if there even was a problem on that brew but, that is all you will know.

The next stage is to brew again, nearly always several times to see if the pattern repeats itself consistently.

If it does, the final thing to ask is, "Should I be changing my defaults or is there another problem going on here that I am missing?"

Not a good thing to read I suppose in these days of instant answers :),
PP
Last edited by PistolPatch on 30 Mar 2013, 20:04, edited 2 times in total.
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Re:

Post by Leafman66_67 » 4 years ago

HbgBill wrote: I just bought a used Blichmann burner and it only has an adjusting valve on top of the regulator. The burner itself is HUGE. It'll be awesome for larger boils.. and I'll play with it for my next small batch.. the burner seems VERY WELL made. I'm thinking I'll really have to learn the valve on that one to avoid both burning off a ton of propane and/or boiling off a lot of my wort.

Anyhow, I believe the result of my experience is paying close attention to where the valve is. With the Blichmann, I'll probably take a felt tip pen and make a mark on the regulator body to show here the valve should be for optimum boils. It'd be all too easy to say this is where I think it was last time and over/undershoot the best for the volume of boil. Agreed, other factors such as air pressure, humidity, etc will play a factor.. but, for now.. I'll concentrate on the valve positioning.
FYI - the Blichman site has a good video on adjusting the flame for optimal output. Great burner - just used mine for the first time on a 40L BIAB in a 58L keggle.
Last edited by Leafman66_67 on 31 Mar 2013, 17:58, edited 2 times in total.
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