Mash plus sparge water volume

[jfk69]

Can anyone please help me wrap my head around, what appears to me, to be a math error that doesn't make sense. I'll simplify it in round numbers to make it easier. I'm finally making the transition to all grain brewing after a year or so of extract brewing. I have my equipment (false bottom 10 gallong Igloo cooler, 9 gallon brew pot, five gallon brew pot, wort chiller etc.).

I'm getting ready to make a SN Pale Ale clone, since I know the taste of the real thing well so I have a comparison and it's a relatively simple recipe. Base grains are 11.25 pounds total. Final volume into the fermenter is 5.5 gallons. Beersmith says for a 60 minute boil I need to start with 7.0 gallons of wort.

Here's where I'm getting confused. Beersmith says 3.5 gallons into my mash, or 1.25 quarts per pound. Check. Makes sense. After initial runnings I expect to lose 20%, or about .7 gallons, to grain absorption. Perhaps another half gallon (or so) to deadspace loss in the tun. So thats 1.2 gallons lost, so approximately 2.3 gallons of wort into the brew pot.

After the initial runnings, Beersmith says do three batch sparges of 1.8 gallons per sparge. I only intend to do two, BUT, based on the programs calculations, this is 5.4 gallons of sparge water. Now assuming since the grain wont absorb any more water, this should all run into the brew pot, giving me a total starting wort of 7.7 gallons (2.3 initial plus 5.4 sparge). This is not the 7 gallons it says I need to start with. Where is the discrepancy? This is driving me nuts. I'm sure I'm overlooking something, and I don't mind boiling longer to get the proper boil off. However, I'd like to end the boil around 6 gallons, 'cause I know I'll have about a half gallon absorbed in the trub and left in the brewpot due to placement of the ball valve.

Am I off my rocker, or am I just missing something? Thanks for any input. I know I'm not going to nail things on my first attempt, but I'm trying to get my head wrapped around this.

 

[MrHadack]

Your grain absorption calculation is wrong, I think.

0.125 gallons per pound of grain is a good rule of thumb. So instead of 0.7 gallons, you'll lose closer to 1.4 gallons with 11.25 pounds in the mash tun. In the VOLS tab on BeerSmith in your recipe, you'll see "grain absorption" in the Mash section on the right. It probably says something like 1.35 for your recipe. And that ~0.7 difference seems to be the cause of your discrepancy.

 

[BigEd]

It's a YMMV situation. Everybody's equipment and methodology is different. The 5.4 gallons of sparge water is essentially correct but it is an average number as there is only so many variables the software can consider. For simplicity's sake your sparge water should be approximately the same as your batch size which here is 5.5 gallons. Start with the given amount and see how it goes. Until you get into it you won't know exactly how much liquid will be lost to absorption, dead space and evaporation. Once you have a few batches under your belt the amounts of water used for your sparge, runoff collected and boil off will come into focus. Then you can make any needed adjustments to your calculations.

 

[HalfmoundBrewer]

I have a similar setup to yours. Here is what I get for volumes when I put in 11.25lbs of base grain.

Strike water 3.77g, Grain absorption 1.35g, Water available from mash 2.42g (first runnings), Tun dead space .25g, Sparge volume 5.07g, Est. Pre-boil volume 7.24g. Boil off 1.0g. Post-boil volume 6.24g. Cooling loss .25g. That leaves us about 6.0g after the boil. Subtract .5g for your trub loss and you have the 5.5g into the fermenter. This is the batch size on the design tab. After the fermentation loss of .5g you get your 5g into the keg.

The trub loss value can really throw off your pre-boil gravity. It just adds more sparge water and doesn't lower the expected gravity. I just put it at .5g and leave it alone. Also be sure to open the mash profile and check "drain mash tun before sparging". It will give you your sparge water volume and you can split in half if you want to do a 2-part batch sparge. Hope that helps.

 

[jfk69]

Okay, thanks folks. Obviously I screwed up my absorption calculation. Had it somewhat right in my head but not on paper. Halfmound, your explanation clears even more up. Time to get off my hind end and go do this. Thanks again.