Why is the boil volume so high in this recipe?

I'm trying to move from extract brewing to AG. Been using a turkey fryer with a 30 quart pot, 5g batches. I thought about moving to partial grain, but after obtaining a 5-gallon igloo mash tun, I'd like to go straight to AG. Before I order my grains, I thought it might be a good idea if I knew what I was going to do with them (what a concept!). These forums are a wonderful resource, so this is where I came for an answer.

My question is: Why is the boil volume so much higher than the batch size on the following recipe (BYO Alpha King Clone)? Is it simply because with 10lbs of grain you will end up with that much wort after using the required amount of water? Thanks in advance for any insight, just trying to figure out how I can do something like this with the equipment I have.

Batch Size: 5.00 gal
Boil Size: 8.79 gal
Estimated OG: 1.056 SG
Estimated Color: 8.3 SRM
Estimated IBU: 69.6 IBU
Brewhouse Efficiency: 75.00 %
Boil Time: 60 Minutes

Ingredients:
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Amount Item Type % or IBU
5 lbs 8.0 oz Pale Malt (2 Row) Bel (3.0 SRM) Grain 54.19 %
4 lbs Pale Malt (2 Row) US (2.0 SRM) Grain 39.41 %
1.9 oz Caramunich III (Weyermann) (71.0 SRM) Grain 1.18 %
1.6 oz Caramel Malt - 60L (Briess) (60.0 SRM) Grain 0.99 %
1.6 oz Caramunich I (Weyermann) (51.0 SRM) Grain 0.99 %
1.6 oz Carapils (Briess) (1.5 SRM) Grain 0.99 %
1.6 oz Melanoidin (Weyermann) (30.0 SRM) Grain 0.99 %
1.6 oz Special B (135.0 SRM) Grain 0.99 %
0.5 oz Wheat - Soft Red, Flaked (Briess) (1.6 SRM) Grain 0.30 %
1.00 oz Columbus (Tomahawk) [14.00 %] (Dry Hop 3 days)Hops -
1.00 oz Cascade [5.50 %] (Dry Hop 3 days) Hops -
0.50 oz Magnum [13.50 %] (60 min) Hops 30.2 IBU
1.00 oz Centennial [10.00 %] (Dry Hop 3 days) Hops -
0.58 oz Columbus (Tomahawk) [12.00 %] (60 min) Hops 31.2 IBU
2.00 oz Cascade [5.50 %] (1 min) Hops 8.2 IBU
1 Pkgs American Ale (Wyeast Labs #1056) [Starter 2000 Yeast-Ale

Mash Schedule: Single Infusion, Medium Body
Total Grain Weight: 10.15 lb
----------------------------
Single Infusion, Medium Body
Step Time Name Description Step Temp
60 min Mash In Add 3.17 gal of water at 170.1 F 154.0 F
10 min Mash Out Add 1.78 gal of water at 198.5 F 168.0 F

Where did you get those volumes - BeerSmith?

All systems are different. The wider the boil kettle, the higher the boil off rate will be. The more BTUs (flame) for an aggressive boil, the higher boil off. And you'll get a higher boil off with drier winter air.

Generally, my boil to finished product calculations include:
1.4 G lost per 60 minute boil.
3.5% lost to chilling
.25 G lost to trub (less or more, depends if I'm using whole hops or pellet)

Is your 5G the finished product, or into the fermentor? Generally its 5.5G into the fermentor for a final 5G batch.

So if you started at 8.3 - lost 1.4 to boil, you're at 6.9.

3.5% to chill moves you to 6.65.
We'll say .5G to trub in the BK - now to 6.15.

Then .5 after fermentation, transferring to bottles - now at 5.65.

So yeah, seems .5G too high. But you could easily boil off too much by accident.

Unfortunately it's just a recipe I located online when searching for Alpha King clones. I was thinking of trying to duplicate it, but it sounds like that is oversimplifying things. Haven't used BeerSmith yet, but after reading so much about it, maybe I should invest. My main issue was that the boil volume listed is higher than I can handle. But after looking at other resources for AG brewing, I didn't think I would end up with almost 9 gallons of wort from 10 lbs of grain.

this is one of those "know your system" things. you need to know how much you boil off over 60 min so you know how much wort to collect. I typically factor in 1gal/hour for my setup, but every system is different. the easy way to do this is to put 6-7gal in your kettle and bring it to a boil for an hour (or 30 min and extrapolate). the RDWHAHB way is to assume about a gallon and wing it on brew day. once you do one boil you'll know for future reference.

I believe the pot I use is 30qts as well. I typically aim to collect 6.5gal of wort so that I have 5.25ish in the fermenter when all is said and done. If you're batch sparging, decide on a mash thickness (grain to water ratio, typically 1.25-1.5qt/lb) and mash. drain your mash, and measure the amount of water. subtract that from 6.5 (or whatever you decide you want as a pre-boil volume) to determine how much sparge water to use. If you're fly sparging, you can just sparge until you collect your pre-boil volume and stop.

why does the recipe you posted have such a high pre-boil volume? who knows. maybe they fly sparge until they reach a certain gravity reading, so they wound up collecting 8+ gallons and had to boil a bunch off. maybe they have a really wide kettle and boil very rapidly, so they lose a lot during the boil. when copying a recipe, that's one of the numbers you have to ignore and calculate for your own system. as suggested, BeerSmith or similar software can do this for you, but if you take a few minutes to figure it out you don't really need the software.

the best advice I can give you is to take careful notes of *everything* on your first all grain brew day. volumes, temperatures, how much water you put in vs how much you get out, how much the mash temp drops over 60 minutes, pre-boil volume, boil off, post-boil pre-chill volume, post-chill volume, how much ends up in the fermenter, etc etc. sounds like a pain, and it is, but if you're diligent about this the first time around it makes your second AG batch go much more smoothly. I also recommend skipping the brew-day beers, at least until you add your first hop addition to the kettle. have extra hot and cool water on hand to adjust temps as needed. AG isn't hard (in fact, I find it easier to deal with than extract in some ways), but it's worth putting the effort in to dial in your system over the first few batches so that you don't have to worry about it down the line.

The recipie volumes are based on the recipie author's system. It has to do with the boil off and the equipment losses for that system, not the grain volume. For comparison, my sytem usually boils off 1 gallon per hour on propane and 1/2 gallon per hour on stovetop. The important items for you to take from the recipie to your system are the grain bill, final volume, and the hops schedule. You will need to calculate your own start volume. The start volume is posted because for those brewers that choose to make small tweaks, how much volume you start with has a *small* impact on hops utilization. Some brewers worry about that. I'm not one of them.

Thanks very much for all of the replies. I will definitely follow the advice regarding the careful notes. Now as for the brew day beers... I guess waiting until hop addition sounds like good advice too (sigh). The explanations make sense to me and are appreciated, thanks again!

I just got a turkey fryer with 30qt pot from Wally World and while I was conditioning it measured boil off at 3 quarts for 1 hour.