I use Brewtoad to work out my recipes, mash calculation, etc. I’m confused on how they are determining boil off. The program asks for a percentage, which I’ve found to be anywhere from 15-25% per hour. Big difference when trying to figure out mash & sparge volumes. Shouldn’t boil off be listed as how many gallons per hour and not by percentage?

I mean, if you boil off 1gal an hour (I boil off much more, but use this example for nice round numbers) and you start with 5 gallons of wort, after 1 hour you’re down to 4 gallons post boil. That boil off is 20%

But if you start with say 3 gallons of wort and boil for an hour you’re still going to boil off 1gal per hour leaving you with 2 gallons post boil, which is 33.3% boil off.

The percentage of boil off isn’t consistent across different batch sizes or boil times. Shouldn’t they be asking for gallons per hour and not a percentage per hour?

I’m trying to work out a 4 gallon recipe and the water calculations are confusing the hell out of me.

Am I missing something here or is Brewtoad just a big piece of crap?

I use ProMash. By default it uses % for boil off, but you can set it to gallons per hour. I suspect that historically, brewers worked their recipes with the % based figure, which works fine if you are using the same equipment every time and boil the same amount of time each batch. The calculators support that, but really should use the per hour figure as the default. Not sure if Brewtoad has the option to change that.

I’ve never used the software you’re referring to, but I don’t see how expressing boil-off in terms of gallons per hour makes any more sense than expressing it as a percentage. Ultimately, the resulting wort OG will always be calculated by multiplying the pre-boil gravity by the quotient of the pre-boil volume and the post-boil volume, and there’s no other way to do it, anyway, that I can figure. So, if your pre-boil OG is 1.040 at 6.5 gallons and you’re expecting to boil it down to 5 gallons, the only real way that I can see to predict the post-boil OG is to divide the larger volume by the smaller volume and multiply that figure by the pre-boil OG. In this case, we’d divide 6.5 by 5, which gives us 1.3- or 130%, if you want to express it as a percentage- then multiply the digits to the right of the zero in the pre-boil OG, which is 40, so the predicted post-boil OG would be 1.3 times 40- or 130 times .4- which equals 52, or 1.052. This is how I’ve always calculated my post-boil gravity, and it’s always been accurate. I’m pretty hard pressed to see how you could possibly calculate your expected post-boil OG without using something like the equation I used above, so it seems to me that your software is really just expecting you to input information that it would otherwise have to calculate for you. You’re just doing an extra step, that’s all. Granted, if your mash efficiency isn’t as good as you expected, then you’re working with a pre-boil OG that’s not what you thought it would be, but that doesn’t in any way invalidate the accuracy of the equation I used above.

We’re not talking about gravity… at all. I’m strictly talking about boil off and whether it should be measured in gallons/hr or percentage/hr. I’m saying that a specific system will boil off a predictable rate of gallons/hr regardless of the batch size… BUT the batch size will directly effect the percentage/hr. So, using percentage/hr of boil off isn’t constant and really shouldn’t be used. Gallons/hr of boil off should be constant and is a better measuring tool.

I think the idea is (at least in Beersmith) that all those predefined values are a “system” or set of equipment that you use for a specific purpose. So this “system” is what I use for a 5 gallon batch sparge, and this “system” is for my 10 gallon BIAB. Not sure if it’s the same in Brewtoad.

So if the idea is creating a set of presets for a given system, then a percentage would work since it’s always going to use the same equipment and volumes. I know in Beersmith it defaults to a percentage but you can override it as an actual volume.

[quote=“mattnaik”]I think the idea is (at least in Beersmith) that all those predefined values are a “system” or set of equipment that you use for a specific purpose. So this “system” is what I use for a 5 gallon batch sparge, and this “system” is for my 10 gallon BIAB. Not sure if it’s the same in Brewtoad.

So if the idea is creating a set of presets for a given system, then a percentage would work since it’s always going to use the same equipment and volumes. I know in Beersmith it defaults to a percentage but you can override it as an actual volume.[/quote]

This is what I’m thinking too. The frustrating part with brewtoad is that they do let you input a custom system (boil off, lautering loss, volume size, etc), but you only get one! They don’t give you the option to create multiple system options. So what if I want to brew a small batch? Or maybe I know in the summer I get much less boil off than in the winter? I need different system options to choose from. I wrote to them and asked. We’ll see what I hear. But again, I think I need to buy some better software.

I haven’t tried a whole bunch of other software so I can’t advocate Beersmith as the best out there but it certainly does exactly what you are saying. You can create profiles for equipment and systems and easily switch between them when creating a recipe and everything gets updated automatically.

If you’re not talking about gravity, then what possible significance could these kinds of calculations have? What do you care if the software doesn’t perfectly predict exactly how much you’re going to boil off if you aren’t talking about gravity? Gravity and the resulting BU/GU ratio is about the single most important controlling factor in any beer recipe as far as I can figure, so if that’s not what you’re concerned about, then what is? I’m lost. I also don’t understand why it is that you think that boil-off rate is constant, but percentage isn’t. That doesn’t really make any sense to me. If one is constant, then the other is constant, too. The only way that would change is if you were talking about different volumes of beer, and even then, the percentage would always be constant within the same batch size between different recipes. I guess I just don’t know exactly what element of the design process you’re trying to zero in on with these boil-off calculations. But no matter what your software is telling you, there isn’t anything you can’t figure out on your own with a calculator, anyway. So if the software is not doing everything you want it to do, just transfer it’s calculations to paper and proceed from there. No software program is going to do everything for you.

He’s saying boil off as a percentage is NOT constant with varying starting volumes.

Boil off rate as a percentage:

5 gallons at 20% is 1gal/hr
3 gallons at 20% is 0.6 gal/hr

Boil off as a constant:

5 gallons at 1gal/hr is…1 gal/hr
3 gallons at 1gal/hr is still…1 gal/hr

dobe is saying his system boil off is the same regardless of the amount in his boil kettle but the software only allows him to model the first example which isn’t accurate.

He’s saying boil off as a percentage is NOT constant with varying starting volumes.

Boil off rate as a percentage:

5 gallons at 20% is 1gal/hr
3 gallons at 20% is 0.6 gal/hr

Boil off as a constant:

5 gallons at 1gal/hr is…1 gal/hr
3 gallons at 1gal/hr is still…1 gal/hr

dobe is saying his system boil off is the same regardless of the amount in his boil kettle but the software only allows him to model the first example which isn’t accurate.[/quote]

Big round of applause!!! Thank you for explaining.

If you’re not talking about gravity, then what possible significance could these kinds of calculations have? What do you care if the software doesn’t perfectly predict exactly how much you’re going to boil off if you aren’t talking about gravity? Gravity and the resulting BU/GU ratio is about the single most important controlling factor in any beer recipe as far as I can figure, so if that’s not what you’re concerned about, then what is? I’m lost. I also don’t understand why it is that you think that boil-off rate is constant, but percentage isn’t. That doesn’t really make any sense to me. If one is constant, then the other is constant, too. The only way that would change is if you were talking about different volumes of beer, and even then, the percentage would always be constant within the same batch size between different recipes. I guess I just don’t know exactly what element of the design process you’re trying to zero in on with these boil-off calculations. But no matter what your software is telling you, there isn’t anything you can’t figure out on your own with a calculator, anyway. So if the software is not doing everything you want it to do, just transfer it’s calculations to paper and proceed from there. No software program is going to do everything for you.[/quote]

You like to steer these discussions down roads that are completely irrelevant to the topic. Of course I can figure these number out myself with a piece of paper, but that’s not my point. My point is there is a flaw with the software. Boil off percentage and boil off rate (in terms of gallons per hour) is most definitely NOT the same. Percentage of boil off is NOT constant. The software should ask the user to list gallons/hr boiled off and NOT percentage/hr boiled off since the percentage is variable and dependent on the initial volume. Gallons per hour is constant (or relatively constant) and SHOULD be what the user is inputting into the software. This would help the user better determine how much initial water is needed, which would then help determine mash and sparge volumes. So yeah… this info is pretty important in how it relates to gravity, IBU, etc.

I’d go into more detail again, but Mattnaik summed it up nicely.

If you’re not talking about gravity, then what possible significance could these kinds of calculations have? What do you care if the software doesn’t perfectly predict exactly how much you’re going to boil off if you aren’t talking about gravity? Gravity and the resulting BU/GU ratio is about the single most important controlling factor in any beer recipe as far as I can figure, so if that’s not what you’re concerned about, then what is? I’m lost. I also don’t understand why it is that you think that boil-off rate is constant, but percentage isn’t. That doesn’t really make any sense to me. If one is constant, then the other is constant, too. The only way that would change is if you were talking about different volumes of beer, and even then, the percentage would always be constant within the same batch size between different recipes. I guess I just don’t know exactly what element of the design process you’re trying to zero in on with these boil-off calculations. But no matter what your software is telling you, there isn’t anything you can’t figure out on your own with a calculator, anyway. So if the software is not doing everything you want it to do, just transfer it’s calculations to paper and proceed from there. No software program is going to do everything for you.[/quote]

You like to steer these discussions down roads that are completely irrelevant to the topic. Of course I can figure these number out myself with a piece of paper, but that’s not my point. My point is there is a flaw with the software. Boil off percentage and boil off rate (in terms of gallons per hour) is most definitely NOT the same. Percentage of boil off is NOT constant. The software should ask the user to list gallons/hr boiled off and NOT percentage/hr boiled off since the percentage is variable and dependent on the initial volume. Gallons per hour is constant (or relatively constant) and SHOULD be what the user is inputting into the software. This would help the user better determine how much initial water is needed, which would then help determine mash and sparge volumes. So yeah… this info is pretty important in how it relates to gravity, IBU, etc.

I’d go into more detail again, but Mattnaik summed it up nicely.[/quote]
I don’t even know exactly where to begin responding to this post. You start by saying that I’m talking about something that’s totally irrelevant to the topic at hand, then you sum up by saying exactly what I was saying about how the final wort volume is totally relevant to gravity, IBUs, etc.??? And I’m sorry to keep beating what in your mind is a dead horse, but what you’re saying about boil-off rate and boil-off percentage being not the same thing is totally beside the point, and you’re missing some really critical points of concern here. Expressing the rate of boil-off as a percentage is just a different way of anticipating the final boil volume than expressing it as a volume per hour. It’s a very simple concept, really. It’s not a flaw in the software at all. It’s simply asking you to plug in a value that’s consistent with your experience. If you’re anticipated rate of evaporation is 1 gallon per hour, that works out to (assuming a pre-boil volume of 1 gallon more than your target post-boil volume for either a 3-gallon batch or a 5-gallon batch) 25% evaporation for a 3-gallon batch or 16.7% for a 5-gallon batch. The program is just asking you to plug in a value that’ really pretty easy to calculate. And if you think that the percentage of evaporation during the boil is so unpredictable, then I don’t know how you’d expect to plug in a value for the volume of evaporation either, because you can’t possibly calculate one value without knowing the other, really. I mean, if you’re confident that you’re going to get 1 gallon of evaporation per hour- and I have to assume that this is the case because you’re so frustrated that you can’t simply plug that figure in and move on- then I don’t know why you can’t simply perform the aforementioned calculation I just did and plug in the value you get from it. It’s that simple. And if you DON’T know how much wort is going to evaporate during the boil, I don’t know how you expect to express it in either format, anyway, so I don’t know what figure you’d plug in for a boil-off volume, either. I’m not talking nonsense here. This is plain and simple math. And just to reiterate, I never said that the percentage of evaporation is the same between all different batch sizes. You’re either putting words in my mouth, or you’re not understanding what I’m trying to say. I have no problem contributing to this discussion, but please don’t tell me that what I’m saying is irrelevant. It’s absolutely not. I just showed you a simple way to fix your problem. If you don’t want to put my advice into practice, that’s your call. Peace out.

Let me put this more simply. I don’t have a problem that needs fixing. I can tweak the numbers to work for what I need. I am simply questioning Brewtoad’s (and many other brewing program’s) use of boil off as a percentage and not as gallons per hour. IMO gallons per hour would make more sense since it’s relatively constant across boil sizes. Percentage per hour is more variable across different boil sizes. The whole point of the software is to crunch the numbers and do the calculations for the brewer. So why should the brewer have to calculate the percentage of boil off when they could simply input their average gallons boiled off per hour?

I don’t know why that program doesn’t offer that option, but it’s just one little calculation, and I’m sure there’s something else it has to offer that other programs don’t, right? Every brewing program is going to have something about it that you may or may not like. It just sounded to me like you didn’t understand how to calculate boil-off as a percentage or something, but I’m sure you’re an intelligent guy and you can figure that one out. Carry on.

Yes, but when you calculate the boil-off in percent you get the amt. in volume also. Let’s say your pot is 32cm in diameter, than your boil-off percentage would be abt. 15% so for 20 litres it should be abt. 3 liters boil-off.

If you then reduce it to 15 liters the surface is still the same so 15% of 15 liters should give a boil-off of 2,25 litres/h