Just before we do the sap, I hope you know what you are doing Caz as I have never heard of doing this before

. The big unknown for me is, "What flavour will the maple sap add to the brew?" I suspect it will be quite distinctive. I won't go into that here obviously. All I will do below, is reduce the grain bill evenly to account for the sugar added by the sappy water.
I also find it hard to visualise maple sap as being watery. Be good to get more info or some pics on what it looks like and whether you scored the 1.020 reading from

.
Secondly, the Sap.
There might be a few ways to deal with this in the BIABacus but I am going to use the way that I find easiest. You may not follow the below Caz but I'll write here what I am doing anyway.
The first line of Section K tells me I am using 9.01 Gallons of 'sappy Water'. The sappy water has a specific gravity of 1.020 and I am assuming that all that SG is caused by sugar. (This may not be true though). This means that the 'sappy water' is contributing 9.01*20=180.2 gravity points
In Section K, we see that after the boil, once things are chilled, we are estimated to have 6.16 gallons. 180.2/6.16=29.25. This means that 29.25 points of your desired 58 (1.058 original gravity) are being contributed just from the sappy water. So we need to go back to Section C and change the 1.058 to 1.058-1.029/25=1.028/75 or 1.029.
When we do this, a flow on effect occurs that you won't see in other programs although it should. Firstly the grain bill obviously drops as the sappy water is supplying a hell of a lot of sugar. Secondly, the kettle Efficiency jumps from 82.2 to 91.6% as the grain required is being washed in more sappy water. Total Water Needed drops from 9.01 gallons to 8.5 gallons as the less grains mean less water is 'sponged' from the kettle.
Let's stop now and have a think...
There's lots of pedantic number stuff that I could talk about here. They are not worth worrying about though. There is one technical thing I'd like to mention briefly. How much does using 1.020 sappy water as your liquor lower the kettle efficiency compared to washing the grain in pure water? Who knows?
The above are interesting intellectual exercises that we can only guess at until real life experiments are done. What really worries me though is...
Recipe Integrity
I think using maple sap could be a really good or a really bad idea.
It could be a good idea if you want to try this as an experimental/specialty beer. It may win first prize. I don't know.
It could be a very bad idea if your intention is to copy that Northern brewer recipe. The sap contributes almost half the 'sugar bill'. Does the sap ferment to a neutral taste? Or, does it contribute some over-powering flavour? I have no idea.
So Caz, great question but I'm unsure that I have any valuable answers.
PP
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