Deadspace vs Slack in Mash Tun

[chrish15]

I'm having trouble wrapping my head around this. Please help!

I have a keggle mash tun with about 1 gallon of slack under a jaybird false bottom, and a dip tube siphoning right down to the last ounce.

If I'm shooting for 1.5 qt/lb ratio mash, and I entered 0 for mash tun deadspace in beersmith...wouldn't the 1 gallon of slack throw off my mash thickness?

If yes, should I over compensate my mash calculation by one gallon and remove one gallon from my sparge water?

I'm confused.

 

[ChuckO]

I ignore the slack space under the false bottom on my system basically because after the initial setting of the grain bed there is some wort above the grain as well. I can't see that there is any difference between the liquid below the false bottom and the liquid above the grain bed. My system is RIMS based and I shoot for 1.5 qt/lb ratio also. Worst case is that it actually comes out 1.33 qt/lb above the false bottom. As long as you are able to properly dough in and stir the mash initially there should be no problem.

Compensating the mash calculation for the slack space will mess up the initial strike temperature and will lead to requiring a temperature adjustment after dough in.

 

[chrish15]

Thank you for the input Chuck. I ended up adding the slack space into beersmith as the deadspace, then subtracted that from the sparge water.

The way I see it, and I could be wrong, is that the gallon underneath a mash screen isn't doing anything to affect the mash consistency above it. Taking away a gallon of water would thicken things up considerably.

My concern is that a thicker mash in a recirculating system could be compacted easier leading to channeling and an uneven mash temp throughout.

 

[RoadKing]

I use a RIMS also. I like my mash thickness at 1.33 Qts. per Lb., so I fill the MLT just to the false bottom then add my measured water. (I have 2 gallons under bottom)
For a typical 10 gallon batch with 16 Lbs of grain, after adding in water under bottom, the ratio ends up being around 1.67 Qts. Per Lb.