Problem with water calculations

[DarkmodeBrewing]

Hi!
I am a fairly new home brewer and have used Brewers Friend for a bit longer than a year.

In my recent batches I have started noticing that the water calculations doesn't add up. I use BIAB and I have configured BF accordingly, (0,66 liters of water I grain absorptions and 4,5 liters of hourly boil-off rate),

I do quite small batches and aims for about 13 liters in my fermenter. So I set my batch size to 13 liters and let BF do the heavy lifting by using quick water calculations. But today I brewed a batch and decided to do som calculations of my own.

I used 4,2 kg of malt, and using the estimate of grain absorption of 0,66 liters per kg of malt, the estimated loss of water should be 4,2 * 0,66 = 2,7 liters of lost water.

However, when I look at the calculations done in BF it says that I need a mash-in volume of 19,5 liters of water and that the estimated pre-boil volume should be 18,57 liters of water in order for me to hit my post-boil volume of 14,07 liters. This checks out because the boil-off rate (4,5 liter/hour).
But! When taking the mash-in volume of 19,5 liters and subtracting 18,57 liters it shows that the difference is 0,93 liters. Since the loss due to grain absorptions should be around 2,7 liters, this throws everything off.

I am no math genius and have relied on BF to do my calculations. Am I missing something or is this how it is supposed to work. Any body else who have experienced this or similar discrepancies in the water calculations? Or am I supposed to be doing the calculations on my own?

Thank you in advance

 

[Donoroto]

I too find water calcs a bit wonky, but they are aware of it and are getting it corrected already.

 

[DarkmodeBrewing]

Well, yeah, something wonky going on. I made a new dummy recipie using the same ammountnof malts. Then the calculations did pan out. Some how the water calculations on this one recipie aleays gets fudged. Even if I re do them…

At least I’ve learned that I need to take greater care and do the numbers my self, to double check them, before I brew…

 

[Donoroto]

@Pricelessbrewing FYI..

 

[Box of Rocks]

Had some screwy numbers in a recipe I rescaled a couple times today. Had to reset my equipment profile, which I had also been adjusting. I recall the water requirement being way to high, but I also recall the grain absorption was zeroed out on the equipment, so not sure where things went haywire.
Two brews ago I was way off on water - needed to boil way longer to hit OG.
Will be sure double check the water requirements prior to brewing tomorrow.
Good to know we should be checking! Anything else that requires us to be wary?

 

[Craigerrr]

I do subscribe to Brewers Friend, but I don't use the brewing software here. The water calculator is part of the reason for that.

 

[Sunfire96]

I've been using an excel spreadsheet for my water levels for the last 6 months. No more water calculator issues for me

 

[Craigerrr]

I've been using an excel spreadsheet for my water levels for the last 6 months. No more water calculator issues for me

Did you create the spreadsheet yourself? I have one as well. Not sure why BF makes it so complicated...

 

[Donoroto]

needed to boil way longer to hit OG.

I was afraid to do that for fear of increasing the IBUs too much. Another 15-20 minutes and OG could have been spot on. Just 4 points low, so no biggie.

 

[Sunfire96]

Did you create the spreadsheet yourself? I have one as well. Not sure why BF makes it so complicated...

Yes. I use it to formulate all of my recipes as far as water goes. I use the same equipment info as BF but the spreadsheet is always correct. I used to calculate the OG as well, but the BF calculator seems correct for that part of the recipe.

And I switched the BruN water for my water calcs

BF is now a fermentables/IBU calculator and recipe/brew session storage for me. And I love the forum of course!

 

[Nosybear]

I was afraid to do that for fear of increasing the IBUs too much. Another 15-20 minutes and OG could have been spot on. Just 4 points low, so no biggie.

I've had the problem frequently, overshooting the amount of water I need. I've made some adjustments to my profile. We'll see if that works next batch. I'd much rather undershoot than overshoot, it's really easy to add water, harder to get rid of it. But I haven't been satisfied with the water calculations here, either.

 

[Donoroto]

@Nosybear So if my post-boil volume is low and gravity high, I just add water to suit? Huh. Simple but previously lost in translation.

Next time, smaller sparge.

 

[Nosybear]

@Nosybear So if my post-boil volume is low and gravity high, I just add water to suit? Huh. Simple but previously lost in translation.

Next time, smaller sparge.

I'd just add water to the wort before pitching. Boiled and cooled, of course, or to the kettle in the last minutes of the boil.