Mash Tun Deadspace & Strike Water Volume Calculations

I've read a number of threads concerning this topic, but was hoping someone could chime in and help answer a few questions I still have.

Here's my setup:
15.5gal MLT w/ false bottom
Volume of liquid UNDER the false bottom (i.e. the amount of liquid needed to fill the MLT until it is level with the false bottom) = 11cups (2.75qts)
Volume of liquid in the Deadspace (i.e. the amount of liquid left in the MLT after draining via the diptube) = 1.25cups

The first volume (11cups) is not deadspace because most of it gets transferred to the boil kettle. The 1.25 cups of liquid left behind is liquid from the "deadspace."

Here's my dilemna though.

If I have 20lbs of grain I am mashing at 1.25qts/lb, I would mash with 25qts (6.25gal). BUT if I don't factor the 2.75qts of water that will be under the false bottom, in actuality the grain is sitting in a mash of 1.11qts/lb. That's a bit thicker than the target 1.25qts/lb. Not terrible, but that's for a big grain bill.

But say I have only 12lbs of grain. At 1.25qts/lb, I would mash in with 15qts (3.75gal). BUT if I don't factor the 2.75qts of water that will be under the false bottom, in actuality the grain is sitting in a mash of 1.02qts/lb. That's a pretty thick mash.

By adding 2.75qts to each amount of strike water, the grain will actually be in a mash that has a ratio of 1.25qts/lb. From what I've read, most guys DO factor that extra volume in. That makes sense to me. I want a 1.25qts/lb ratio so I need to make sure that's what I've got in contact with the grain. But I still have questions.

1. Does this change in volume in the MLT have any detrimental effect on the finished beer? A "thicker mash" tends to produce beers with more body while a "thinner mash" tends to produce beers with less (I know this is a simplification).

2. If I factor for the additional 2.75qts under the false bottom, I know the grain is still technically in a 1.25qt/lb mash, but does that extra volume of liquid affect the fermentability/body in the finished beer?

3. I fly sparge but I do NOT recirculate (no pump...yet). So if I simply sparge until I hit my target pre-boil volume, will there be any issue with the "semi-diluted" wort that was in the MLT? That extra 2.75qts of water that was added to the mash will dilute the wort strength a bit, so making higher gravity beers or doing a "no-sparge" could be a little bit more tricky.

Am I seeing this right? I know. I know. Before you say it. RDWHAHB. But I also want to make sure I'm seeing this right. Thanks in advance.

Add the extra 3 QTS. Sparge with normal volume. Adjust your boil time to end up with the final volume that you want by boiling off that extra water. This is one of many ways to compensate for the volume under the false bottom. Or u can add more grain for a larger but equal gravity product.

Thanks Fred. I figured that's one way to do it, especially when I'm doing a big beer and definitely a no-sparge beer. That helps answer question number three for sure.

I'm still wondering about questions 1 & 2 though. With "normal" strength beers, I probably won't need to add extra grain or boil for longer. With my method of fly sparging, I don't have a "normal volume" to use. I make up a big pot of sparge water and slowly add it to the mash while I'm draining out through the ball valve. I prepare more than I need and simply sparge until I collect my target volume. Doing it this way means I collect wort until I hit the targeted 7gal. That 7gal will be the same gravity whether I add the extra 2.75qts or not. Adding more water up front means the overall gravity will be lower throughout. But because I'm using less sparge water, the gravity will still be the same (i.e. 4gal of 1.060 mashed wort + 3gal of sparged wort VS. 3.25gal of 1.070 mashed wort + 3.75gal of sparged wort).

Hopefully I'm not confusing people. If the way I'm understanding it is correctly, I'll end up with the same volume and gravity of wort either way. Adding more water for the mash means I won't need to sparge as much and vice versa.

I'm still wondering though how the extra volume of water affects the mash chemistry and the other two questions I asked above. Do you or someone else have an answer or for that? Thanks again.

I dont think ratios are that important for your setup......small % change due to deadspace isnt going to kill you.

Do you have a brew software like Beersmith??

I've been doing a bit of research on this question. I've been reading on Kaiser's website and his experiments with mash thickness. Hebdid identical experiments with 1.21qts/lb and 2.54qts/lb. He found no difference in attenuation. That's a pretty big difference in thickness.

The main difference he mentioned was the efficiency. The higher ratio made for a more efficient lauter. The thicker mash was less efficient. I've also been reading that the main factor in fermentability of the wort is the temperature of the mash. This is what I've read elsewhere and heard on Brew Strong as well. Generally a higher temp results in lower fermentability and vice versa.

I think the reality is that the BIAB folks "mash" with a ratio close to 4qts/lb and they have no problems. So, I'm not going to worry about it. I'm going to mash with the ratio I'm shooting for (i.e. 1.25qts/lb) and then add to that the 2.75qts of extra water to fill the deadspace.

Any concerns?