Mash tun losses

I'm trying to determine the amount of wort lost to my mash tun. I've seen absorption loss numbers ranging from 0.1-0.2 gal/lb. If I am fly sparging, how can I accurately find the number for my setup?
Unless I'm overthinking this, I figure I would need to do a one-time dough-in and drain to check the yield of liquid and sacrifice the grains in the name of quality.

Any other suggestions?

You should be able to figure out just by brewing a beer. You'll obviously have to run through one beer before knowing. If you know the amount of water going in, and you know the amount coming out, you have your grain absorbtion. You also need to factor in how much is stuck underneath your manifold. That can be done by just filling the mash and emptying it with the spigot as much as possible, then measure the amount of water you had left over.

SoFlaBrewer said:

.......and sacrifice the grains in the name of quality.

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Sorry, not a real brew by the numbers guy here, but this sounds like a very bad idea!

Like suthrncomfrt said, just do your dough in, let it convert, and then drain. How much did you get out? How much grain did you use? You got your number! Now adjust the amount of water needed for sparge to hit your target volume and you are golden.

I'm just thinking that there is no way to measure the yield while I have sparge water rinsing the grains at the same time. I don't want the grain bed depleted of water, correct?
Big picture-- I'm trying to determine the amount of water I need for my pre-boil volume. Part of that number is absorption loss.

SoFlaBrewer said:

I'm just thinking that there is no way to measure the yield while I have sparge water rinsing the grains at the same time. I don't want the grain bed depleted of water, correct?
Big picture-- I'm trying to determine the amount of water I need for my pre-boil volume. Part of that number is absorption loss.

Click to expand...

I did realize after I posted that I was talking more about batch sparging which is what I do. I don't mind letting the grain bed run dry because I am just going to add more water and stir. Honestly though, .1 g/lb has worked for me just about right on.

I guess I always thought that you can't get less sugar by adding too much sparge water and not collecting it. For example, if 4 gallons is the exact right amount you can add 4 gallons and collect it in the kettle. If you add 5 gallons and collect 4 gallons, that 4 gallons is going to pick up the same amount of sugar that it would if there wasn't a gallon sitting on top of it. There could be some mixing within the grain bed but I think that would be negligible. Then you can still drain the last gallon into a pitcher to do your calculations.