Add false bottom dead space to strike water amount?

[neb_brewer]

I bought a Brewer's Best kettle and one of their false bottoms to go with it to use as my mash tun. The false bottom has 2.5 gallons of dead space. If I'm brewing a small beer like a Cream Ale that only calls for 3 gallons of strike water for the mash, do I just need to add 2.5 gallons to that? So 5.5 gallons of strike water?

If that's the case, will there be any negative impact from having that much water at the start?

 

[chickypad]

Wow that's a heck of a lot of deadspace for a 5 gal batch, how big is your pot? For comparison I had 2 gals deadspace on a 15 gal mash tun for 10-12 gal batches. Are you recirculating? If you don't add additional water to account for the deadspace your mash is going to be way too thick so I would take at least some out of your strike water, or you may just want to do a full volume mash. Then the main thing would be watching the mash pH. Hopefully you have a diptube to pick up the wort from under that false bottom or your brewhouse efficiency will suffer.

 

[neb_brewer]

Its a 15 gallon kettle but I'm doing 5 gallon batches normally. I am recirculating during the mash and will have a dip tube under the false bottom. I also fly sparge.

I am concerned about efficiency as I always had really great efficiency with my old setup (keggle with a false bottom with almost no dead space).

 

[Smellyglove]

You could just decide on a mash thickness ratio. For example if you're going 3L/kg and use 5kg malt then it would be 15L of strike water, But since you have a deadspace (let's just say 2L) then you add that to the 15L, and divide by grist again to achieve 3L/kg

So 5*3 =15L
15+2= 17L
17/5= 3.4
This will give you a mash thickness of 3L/kg above the FB, but "total/overall" ratio will be 3.4kg/L. (17/5).

Then use rest of the water for sparging. This way if you're using any software just enter 3.4 as liquid/grist ratio.

 

[brewbama]

I use rough math and split the dead space between the two (5 gal batch):

7.5 gal required pre boil

1.5 absorption
.5 dead space
= ~9.5 gal required total

I split the total required this way:

~5.5 strike
~4 sparge

I don’t get too worked up about qts per lb. Works great.

 

[SoCal-Doug]

If you are recirculating constantly, you don't need to think about a "mash thickness". The grain bed will compact the same density no matter how much water is in the mash system. Mash thickness is a thing to consider if you are simply adding strike water to the grain and letting it sit static for the duration of the mashing (like in an igloo cooler). In a recirculating system, the grain sees a constant density. In theory its almost backwards, having more water on top of the grain during recirculation (or having a higher flow rate), actually compacts it slightly more, thereby making it "thicker". But in 5 to 10 gallon systems, its not a large enough factor to even think about.

That being said... You need enough water to keep flowing through the grain, allow for what the grain will absorb, and fill your tubing, pumps, herms coils, rims tube, false bottom area, and any amount of wort you want to always be on top of the grain bed.

In most recirculating systems, there is no "lost" wort or "dead space". Fresh sparge water comes in as the mash drains. The wort is being "exchanged" for water during the sparge. The fresh water comes in from the top as it slowly drains out of the bottom. At the end of the sparge, everything is left with fresh water (yes, there is always a tiny about of wort left). So, back to mash water...

Grain will absorb approximately 0.12 gallons of fluid, per pound of grain.
There is gaps between all the kernels and bits of grain that need to be filled.
A tiny bit of water will evaporate during the mash
So... Using a 1.25 quarts of water, per pound of grain, is a great starting point to make sure the gain is fully submerged and absorption is considered.

Consider the following example as a starting point for calculating the mash water needed (these are numbers from a batch I did yesterday)...
​

Total grain weight: 8.43 pounds
Water needed for the grains (1.25 quarts per pound X 9 pounds): 2.63 gallons (10.54 quarts)
Tubing, herms coil or rims tube, pump, valves, whatever: 0.5 gallons (you need to measure this in your own system)
Area under the false bottom: 0.25 gallons (your's would be 2.5 gallons)
How much water you want to maintain on top of the grain bed during recirculation: 1.25 gallons (you need to calculate this based on your kettle diameter. most people like about an inch and a half)

Therefore, total mash (strike) water is: 4.63 gallons

At the end of the mash, sparge until your preboil volume is reached. If for example your preboil volume is 7.36 gallons, you will need at least 3.73 gallons of sparge water. 7.36 - 4.63 = 1.7 PLUS the amount absorbed by the grain (1.01 gallons) = 3.73. Of course, give yourself an extra couple gallons extra sparge water.

Hope this helps

 

[neb_brewer]

That's really helpful. I finished my brewday before reading all responses, but essentially did what you described. I started with a little higher water to grain ratio of 1.5 and feel this was too much. I'll go with 1.25 next time.

This was a re-brew and this beer's OG was about 6 points lower than the last one that I made. Just like with any other change to process, I imagine it'll take me a few brew days to get things dialed in again.