Beersmith Boil Off

[thdewitt]

I have a question regarding boil off. Does anyone know if the size your are boiling affects the amount per hour than boils off? In Beersmith you put in a percentage like 15% for the boiloff. But then if you change the batch size from 5 gallons to 10 the boiloff goes up also. This doesn't seem right to me. It seems like if you have a 15 gallon pot and you boil 5 gallons and loose 1 gallon in an hour that if you boiled 10 gallons, you would also loose 1 gallon in an hour. It seems like the surface area exposed at the top of the pot is the same and the temperature is the same. I am just a layman. am I missing somthing? I keep on ending up with much less beer than 6 gallons on my "6 gallon" batches.

Thanks,
Tom

 

[bull8042]

Well, I think I use 13% for my setup, but I definitely understand your concern. Unfortunately, I had the same question and still don't have an answer. Maybe someone has the answer will chime in for the both of us..... (Hey Brad, you around here these days?)

 

[TwoHeadsBrewing]

Figure out what your boiloff is, then adjust the precentage under your equipment setup. To the right of the Boil-Off % text box there is the actual amount in gallons. I find the estimate of 9% to be pretty close. I suppose those two fields should be both editable and linked, so that changes to either effect the other. Pretty easy change to make, I'd be happy to do it for Brad...should take me about 2 minutes (hint hint!).

 

[wildwest450]

Are you guys using candles for boiling? My boil off is 23%.

 

[JVD_X]

You do boil off more with 5 gallon batches than 10+. I found I can mitigate that issue by establishing a strong boil for whatever size batch and then turning down the gas so that the boil is still rolling but not excessively.

Alternatively you can set up different equipment profiles - one for 5+ gallons and one for 10+ gallons with different boil off percents.

In either case, as long as you are getting over 60 minute boils you can boil just long enough to reach your specific gravity goal.

 

[bull8042]

I understand that, I just don"t understand the percentage. ie, you have a keggle with 10 gal of water, boil off is set to 10% per hour. That is 1 gal per hour..... Same keggle with 5 gal of water. At 10% per hour, that equates to 0.5 gal. Same vessel, same heat source, same liquid.
That is what I am having trouble understanding.
So, go ahead and give me a simple explanation that I am overlooking that is going to make me feel like a moron.

 

[thdewitt]

that is exactly what I was getting at. We should be able to set a gallons per hour setting instead of a percentage. It just makes more sense that if all other factors are equal the amount of water in the vessel does not mater.

 

[ajf]

You're not missing anything. A % boil off rate is hopeless if you make different size batches.

Are you guys using candles for boiling? My boil off is 23%.

That's nothing! When I switched from a % to gallons per hour in Promash, I ended up boiling off 15 gph (according to Promash).

-a.

 

[bull8042]

You're not missing anything. A % boil off rate is hopeless if you make different size batches.


That's nothing! When I switched from a % to gallons per hour in Promash, I ended up boiling off 15 gph (according to Promash).

-a.

Holy doo doo! What are you boiling with? Don't you think you should return that secondary thruster to NASA before you get into trouble?!?!

 

[ajf]

Holy doo doo! What are you boiling with? Don't you think you should return that secondary thruster to NASA before you get into trouble?!?!

I had Promash set up to boil off at 15% per hour. I realized it was ridiculous, so I changed the units to gallons per hour without changing the value. (It kept the 15)
It took me about 5 minutes to realize something had gone seriously wrong, and another 5 minutes to find and fix the problem.
Thankfully, I didn't formulate a recipe with that boil off rate.

-a.

 

[FlyGuy]

To the OP, you are correct -- Beersmith does calculate evaporative losses incorrectly, and this is a known limitation with the software. I am not sure why it has never been fixed.

The amount of water lost to evaporation during the boil is a function of many things, but the size and shape of the pot is a big factor. So is the vigour of your boil. If those two things are kept relatively consistent, then a loss of water per hour is the best way to estimate your boil-off rate.

In my Beersmith application, I have multiple equipment profiles set up for different batch sizes to overcome this limitation.

 

[bandt9299]

I also use beersmith and set the boiloff @ 15 percent, which is right on 95 % of the time, 7.33 gallons boiled down to 5.5, I am going to 10 gallons real soon and when I put an 11 gallon recipe in, it has me boiling 14 gallons, someone must have some experience with this, (making the 10 gallon jump). I hate to be the gunnea pig. I will make my first 10 gallon recipe a low IBU, so if I have to boil longer, no big deal. But still curious.
Thanks

 

[TwoHeadsBrewing]

I also use beersmith and set the boiloff @ 15 percent, which is right on 95 % of the time, 7.33 gallons boiled down to 5.5, I am going to 10 gallons real soon and when I put an 11 gallon recipe in, it has me boiling 14 gallons, someone must have some experience with this, (making the 10 gallon jump). I hate to be the gunnea pig. I will make my first 10 gallon recipe a low IBU, so if I have to boil longer, no big deal. But still curious.
Thanks

I use 9% for 11 gallon batches with my sanke keggle system. This is just about right, and depending on the weather sometimes I end up with even less boiloff. Just for your first batch, I'd try 11% and see how that works for you. What kind of kettle are you using, and is it the same as your kettle for the 5 gallon batches?

 

[bandt9299]

Yes, I also have 2 sanke keggles, the new one just had the couplings welded in yesterday, once I order a ball valve and thermometer, I'm good to go. Thanks for the info.

 

[rocketman768]

Boiloff rate as a percentage is not right as a concept. This means the more liquid you boil off, the slower the boiloff occurs. This is clearly not right. If anything, boiloff might increase slightly as more liquid is evaporated. In my opinion, boiloff should be a fairly constant rate, and not a percentage which implies exponential decay.

 

[bull8042]

Figure out what your boiloff is, then adjust the precentage under your equipment setup. To the right of the Boil-Off % text box there is the actual amount in gallons. I find the estimate of 9% to be pretty close. I suppose those two fields should be both editable and linked, so that changes to either effect the other. Pretty easy change to make, I'd be happy to do it for Brad...should take me about 2 minutes (hint hint!).

Why not contact Brad and offer your solution? It would be really nice if the issues identified collectively here were incorporated into some sort of update for the program.

 

[mikfire]

Actually, boil off as a percentage makes sense as long as the volume is constant. It took me a while of thinking about it, but it finally occurred to me that boil off percentage is based on the total volume of the kettle, not on how much liquid you are actually boiling.

This makes sense to me because, as FlyGuy said, the amount of boil off I get is mostly affected by the size and shape of the kettle and, to a lesser extent, how much heat my burner can produce.

So. If I have a 10 gallon kettle (and I do) and I boil off about 1g/hr (which I do), then my boil off percentage is 10%. So far, this has worked quite well for me. Using this number, beersmith gives me a fairly accurate estimate of how much water I will need to get a 5.5g batch.

 

[The Pol]

Boil off is pretty much a constant... but not a %.

This has been addressed before...

Boil off is a result of surface area, humidity, temp. etc... but can never be utilized as a % across differing batch sizes.

If you boil off 1.5 gallons/hour as I do, that does not change significantly with a larger batch. If your temp, surface area, humidity etc... is the same, the boil off rate is a constant 1.5gal/hour in my case... not 15% or 20% of the starting volume.

Figure out your boil off rate/hour and use that as a constant. My boil off is about 20% on a 5 gal. batch (1.5 gal/hr)... but that doenst mean that it will DOUBLE to 3gal/hour if I do a 10 gallon batch, get my point?

 

[JVD_X]

Pol - My experience has been very different. I can boil off 2 gallons an hour with 5 gallon batch but barely 1/2 gallon with 15 gallon batch.

 

[The Pol]

Pol - My experience has been very different. I can boil off 2 gallons an hour with 5 gallon batch but barely 1/2 gallon with 15 gallon batch.

It has to be a difference in the vigor of the boil then. The BTUs applied vs. volume boiling.

Look up what affects the evap. rate of a fluid. The quantity UNDER the surface doesnt matter, the only thing evaporating is the surface, which is tied to surface area and atomospheric conditions.

Also, your experience would even FURTHER discount the idea that boil rate is a constant %.

If I boil off 2 gallons on a 5 gallon batch, the myth that boil off is a % of volume would say that I would boil off 4 gallons on a 10 gallon batch.

This was one of a couple reasons that I got ProMash... every time I changed my volume, by even a little, BS wanted to change my boil off, so Id have to go manually calculate the proper % again to make it a constant gals/hr.

EDIT: this is from an article on this sort of topic. This is what I have always concluded to be the major factors in evap. rates.

NEWTON BBS receives many inquiries about "evaporation rates" of water.
While it seems to be so simple, the rate of evaporation is a very complex
phenomenon. It depends upon so many parameters that it is virtually
impossible to give an unqualified satisfactory answer. A partial list of
variables that affect the evaporation rate is: temperature, relative
humidity, surface area, air speed, air direction, presence of solutes in the
water, cooling produced by the evaporation, ...

 

[jds]

I've found that with my equipment, if I achieve a vigorous rolling boil, I boil off about 1.5 gallons per hour, regardless of whether I start with 7 or 13 gallons in my kettle.

In Beersmith, under equipment details, I've deselected the "calculate boil volume automatically" option. That way, I have to think about it for each brew, and make sure I'm collecting the correct amount of preboil wort. That also means I have to think about absorption by hops, unless I soak and rehydrate them first.

Reportedly, this will be changed in the next release to allow one to set boiloff as a fixed volume rate (gal/hr) instead of a percentage.

 

[The Pol]

I've found that with my equipment, if I achieve a vigorous rolling boil, I boil off about 1.5 gallons per hour, regardless of whether I start with 7 or 13 gallons in my kettle.

In Beersmith, under equipment details, I've deselected the "calculate boil volume automatically" option. That way, I have to think about it for each brew, and make sure I'm collecting the correct amount of preboil wort. That also means I have to think about absorption by hops, unless I soak and rehydrate them first.

Reportedly, this will be changed in the next release to allow one to set boiloff as a fixed volume rate (gal/hr) instead of a percentage.

And this is how it should be. If anyone is seeing a much lower rate with an increase in volume, it is because the boil, BTU/VOL. is much lower and you have lost vigor in your boil. It has nothing to do with the volume persay... BUT more with the fact that you are lacking the BTUs to obtain the same boil in the larger volume as you obtain in the smaller volume.

The science behind boil off is always the same... you will always have a constant #gal/hour regardless of your starting volume. NOW if you see a difference, it is not a deficiency in the science or the math, it is a deficiency in the process (ie lack of vigor/BTU)

 

[FlyGuy]

The science behind boil off is always the same... you will always have a constant #gal/hour regardless of your starting volume. NOW if you see a difference, it is not a deficiency in the science or the math, it is a deficiency in the process (ie lack of vigor/BTU)

While I generally agree with you that boil-off rate tends to be fairly consistent and is not greatly affected by the volume of the boil, it should also be considered that the amount of empty space in your boil kettle will affect your boil-off rate. A full kettle will lose more to evaporation than a nearly empty one (all others factors constant, such as boil vigour). This is especially true of tall, narrow pots/kettles (anyone that has ever boiled in a 7.5 gal keg will have seen this).

Regardless, while neither approach is ideal, considering boil-off rate to be constant (for a given vessel) is far superior to using a %. This point has been brought to Brad Smith's attention before -- not sure why he hasn't made the change in Beersmith.

 

[The Pol]

You will see that several brewing programs use % to calculate boil off... how this ever became an accepted way of determining it, I dont know.

You are obviously not going to boil off 2x as much liquid in a 10 gallon brew as you do with a 5 gallon brew, but that is exactly what % boil off will tell you.

And yes, there are variables that will play a small role in the boil off rate depending on how full the vessel is, the speed of the breeze on the day that you brew will affect it too... but I m certain that was not the intent of the % boil off calcultion, becuase it doenst consider humidity either.

 

[bakins]

The science behind boil off is always the same... you will always have a constant #gal/hour regardless of your starting volume.

Okay, If I'm reading this correctly, my amount boiled off should be the same between a 5 and 10 gallon batch? All things being equal? Ie, if I boil off 1 gallon/hour in a 5 gallon batch, with a 4500W element at 60%, I should boil off a gallon/hour with same element at same setting for a 10 gallon batch?

 

[The Pol]

Okay, If I'm reading this correctly, my amount boiled off should be the same between a 5 and 10 gallon batch? All things being equal? Ie, if I boil off 1 gallon/hour in a 5 gallon batch, with a 4500W element at 60%, I should boil off a gallon/hour with same element at same setting for a 10 gallon batch?

Well, almost.

#1. If you use the SAME setting for 5 gallons as you do for 10 gallons, you will probably boil of LESS

(note this is the INVERSE of what BeerSmith would tell you by using a % boil off)

#2. You need to look at this as BTU/LB, why? If you use the SAME # of BTUs and increase the volume you are heating, you will eventually boil off NOTHING.

#3. You will likely get CLOSE to the same boil off if you keep the PID setting the same. Most likely you will boil off LESS, to a small degree.

#4. Put some water in there and test it!

 

[bakins]

#4. Put some water in there and test it!

Tried it last night - well not fully - and I need to set the PID on 70% to get "vigor" like i did in my old pot at 60%. Didn't have time for a full test, but I'll let you know what I find out.

 

[The Pol]

Tried it last night - well not fully - and I need to set the PID on 70% to get "vigor" like i did in my old pot at 60%. Didn't have time for a full test, but I'll let you know what I find out.

Cool cool... I mean you cant take what I say as BLACK AND WHITE... obviously logic dictates that with the same BTU applied to a LARGER volume, there will be a difference. But, logic dictates that most brewers adjust thier burner to get the same relative vigor, making te boil off differences on a HBing scale, negligible.

I guess what I was really getting at is that you will not INCREASE your boil off RATE with MORE wort... logic would dictate that you would reduce it since you are decreasing your BTU/LB ratio. In our cases Bakins, we can simply add 10% or so to the output and probably get the same boil off.

But why wouldnt we need to DOULBE the power? Well, maybe this is the same principle as a mult-engine aircraft operating with ONE engine inop.

If you have a climb rate of 2,000 feet/min with TWO engines, you will NOT have a climb rate of 1,000 feet/min with ONE engine operating. Why?

The aircraft NEEDS a certain amount of thrust to MAINTAIN level flight at a said airspeed. It then USES excess thrust to accelerate and climb.

If your excess thrust is that thrust provided by the second engine... without it you do not HALVE your climb rate, you lose the ability to climb at all.

This is why I dont think you need to double the power to achieve the same rate if you double the volume. You simply need to DOUBLE the EXCESS BTU's to keep the fluid vaporizing at the desired rate.

If I want to doulbe the climb rate in my a/c I do not need to double the thrust rating... I only need to double the EXCESS thrust... aha

 

[bakins]

But why wouldnt we need to DOULBE the power? Well, maybe this is the same principle as a mult-engine aircraft operating with ONE engine inop.

I did some research. Don't have links handy, but basically, theoretically, the boil off rate is constant with BTU/hour, regardless of volume. Nothing to do with time to boil -- that takes more watts. My new pot has a different geometry and is not insulated (yet - it's just so shiny...), but I read and rered a bunch of stuff and all pointed to same thing.

Found a link:

http://thirstyhomebrew.org/phpBB2/viewtopic.php?t=392&sid=aaa5bbe48311dc9adb64d75b5bdcb07e

"If I want to boil off 2 gallons per hour, I can type this into google:
2 gallons * (1 gram / 1 ml) * (2260 joule / 1 gram) in BTU

Google will convert the units and do the calculation for you. 2260 J/g is the heat of vaporization of water."

That matches up with other stuff I read.